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What is a constellation, exactly?
Well, it's just a Man's invention. Constellations do not exist in nature. When the ancient people observed the night sky, they noted that some stars make geometrical figures. Their vivid imagination caused them associating these figures with animals, objects, or legendary human characters. Apart from some rare exceptions, this resemblance is very debatable.
As ancient people used to think the Sky was just a huge dome above the Earth, they made the mistake to think the stars within a constellation are actually close to each other. We modern people, too, tend to do the same error, even when accepting the sky is not a "celestial dome" but a boundless extension of space outside the Earth. Popular media contribute to all this, for example Sci-Fi stories telling us a space traveller can easily go to a constellation to another with its spaceship. Actually, constellations are just simple areas in the sky whose boundaries were definitively decided on in year 1922 by an International Convention — before that, those boundaries were quite indistinct. Within each area, stars are not close to each other (apart from those grouped in clusters, see further); they aren't even at the same distance to us. One star that seems coupled with another in the sky can even be 10 times more distant from us than its neighbor. The typical figures of the constellations would totally disappear if we could go out of the Solar System and see, for example, the sky at a distance of 100 light years from Earth. All the visible stars in the sky pertain to our Galaxy, more precisely the galactic portion closest to the Solar System — the more distant stars visible without binoculars or a telescope are about 3,000 light years from here: the whole Galaxy is 100,000 light years wide.
Also note that the stars within a constellation are neither of the same luminosity, nor are they of the same color; two stars can appear the same brightness but one can actually produce 1,000,000 times more light than the other, but is 1,000 times more distantnote Not 1,000,000 times; remember the Inverse Square Law. Colors vary from red to light blue, passing throughout orange, yellow (our Sun is yellow), and pure white. note Green stars do not exist. This coloration is tied to the temperature of the stars' surface: curiously, red stars are the "coldest" (about 4,000 C°), then the orange, yellow, white, and finally the hottest of them all, the blue ones (up to 40,000 C°). Our Sun is about 6,000 C°. Finally, it's worthy of note that the stars making the figure of a constellation do not appear with the same luminosity when live-observing, note And, of course, there are NOT lines linking them, they are only a means in astronomy books to aid the reader to better memorize the figure, and different books can link the stars of a constellation in slightly different ways. and that they are not the only stars of the constellations: they contain dozens and sometimes hundreds of other fainter stars visible to the naked eye, and millions more when watching with a telescope.
THE 88 CONSTELLATIONS
Only very few constellations are familiar to laymen. Most of them are known only by astronomers or space lovers. This is justified though, both because most constellations are faint and hard to recognize, and because even the brightest ones are difficult to see for a non-expert when living in a city or even in a town — we'll not talk here about the notorious light pollution. 48 constellations were invented by ancient Greek (even though many were already conceived before that), and made official in the first century A.D. by the famed astronomer Ptolemaeus. Obviously, they are mainly in the Northern celestial hemisphere. note The two celestial hemispheres do not coincide with the two terrestrial ones. An U.S. or European observer can also see some constellations that are below the celestial Equator, but certainly the northern ones are the easiest to see for her/him. The exact opposite for an Australian or South-African observer of course. Since the 1600s, other astronomers have invented all the remaining 40 constellations, plus others that aren't today anymore (because they were not accepted by the International Convention above). Modern constellations are usually fainter than the classical ones, and were created to fill the "empty" areas in the sky which were not assigned to any constellation in ancient times — even though some were created by taking some stars away from ancient figures, for example the Southern Cross which was originally part of a larger constellation called the Centaur.
Other than the common name, constellations also have their official Latin denomination. For example, the Great Bear becomes "Ursa Major" in Latin. Their stars are named by several means. The main ones are listed by Greek letters (the "Alpha" is usually, but not necessarily, the brightest note In many constellations there's not a star clearly brighter than the others; in such cases the Alpha is often the star that signs the head of the human/animal character portrayed. The choice of the other stars named with the following letters (Beta, Gamma, Delta, etc.) tends to be merely arbitrary.); numbers, Latin letters, and acronyms are also used to list the stars in a constellation. These letters/numbers are always followed by the latin name of the constellation (with the Genitive declension). The brightest / most notable stars have also their own name (usually Arabic, sometimes Greek or Latin). As a consequence, the most famous stars have more than one name: one or more common names, plus its official Greek letter, its official number, and (if is a "variable star") a couple of Latin letters. As examples, the brightest star of the aforementioned Centaur is called Alpha Centauri (greek name), Rigil Kentaurus or Toliman (common names), and has also its official number.
Here we'll divide the 88 constellations in subgroups for convenience. To learn more about constellations in general, see here.
Constellations near the North Pole
These constellations are called "circumpolar" (liter. "around the Pole") and can be seen all year round from North American and European latitudes. note Even though their more southern part can go below the north horizon if you're watching the sky from below the +40° terrestrial latitude. During the night/the year you can see them turning around the northern Polar Star (which signs the celestial North Pole). The latter is the only star apparently fixed in the Sky, and points toward the North direction of the Earth.
Ursa Major & Ursa Minor: the Great and the Little Bear. These are the only constellations in the Northern Emisphere whose figures are known even by laypeople. What is less-known is, the two celestial bears have given their name to the Arctic (Arctos in Greek means bear), and indirectly the Antarctica — literally the "anti-bear". However, only the Great Bear (or more simply, "the" Bear) is easily visible in the Sky. If you want to see the Little one you must go out of cities, and even so you have few chances to identify it if you're not a skilled watcher. Moreover, the way books tell you to find the Polar Star (by using the two Great Bear's stars that seem pointing toward it) is not always easy to apply in Real Life. So, it's not surprising that many people say never to have seen the Polar Star.
Ursa Major (meaning the "greater she-bear" in Latin) is the biggest-by-area constellation in the Northern Emisphere and the 3rd in the whole sky. However, the familiar group of seven stars people associate with the the Great Bear is only the brightest part of the constellation, and the only one non-astronomy books usually portray. It marks only the hindquarters and the (overly long) tail of the animal, while the remaining body is much more extended but signed by faint stars (the bear's paws are marked by three couple of starlets), and gets usually unobserved by non-expert watchers. The constellation appears high in the Sky in Spring, but may be low near the North Horizon (or even below it) in Fall. The group of seven bright stars is called the Great Dipper or the Great Plough in English, but is variably named across the languages and dialects: the Great Car, the Great Pan, the Great Ladle, and so on. One of the stars of the "tail" is a famous double-star: Mizar. Its weaker companion, Alcor, is usually distinguishable from Mizar (the main star) only by using the binoculars or a telescope, even though some sharp-eyed people can tell the two stars apart with their naked eyes. note Double-stars are stars so-close to each other in the Sky they visually appear like one single star. Triple and multiple stars are also existing in the firmament. In some cases they are really close in the space and tied by gravity (the really double / multiple stars); others are only incidentally in the same perspective but at different distances from us. Mizar & Alcor belong to both cases: they are not close to each other in the space, but each one is made of two or more stars which are really orbiting together in the space. Ursa Minor (literally "the lesser she-bear"; also called the Little Dipper, Plough, Pan, Car, Ladle, etc.) is so-called because resembles a miniature version of the "great dipper" but with a more curved "handle". Only three of the seven main stars are visible from a city or a town: the Alpha (aka the Polar Star), and the two at the opposite end. Since the Polar appears still, the Little Bear seems turning around the North Pole with the end of its "tail" fixed in the Sky. Contrary to what is often believed, the Polar Star is not the brightest star in the Firmament (the record-holder is Sirius in the Great Dog), nor is it an expecially-luminous star. And is not actually fixed in the Sky; it too turns imperceptibly around the actual North Pole. Finally, it has not always been THE polar; see below to learn why.
Draco: the Dragon. Like the Great Bear, the Dragon is one of the biggest constellations in the Sky. It's a sort of large "inverted S" which signs the snake-like body of a mythical dragon; its head is marked by a small quadrilater at one end of the "S". Unlike the Great Bear, the Dragon is faint and difficult to recognize; it is higher in the sky in Summer, and would be visible next to the the Little Bear — while the dragon's tail wedges between the two bears. The Dragon's Alpha star (unusually, not the brightest star of its own constellation) was in ancient times the Polar Star because of the Precession; the modern Polar Star has owed this privilege only since about 500 years. The next 20,000 years the Polar would be Vega, in the Lyre. Draco has also included the north pole of the Ecliptic — for the record, the Ecliptic is the circular route covered by the Sun during its apparent yearly "trip" in the firmament, but see the "Zodiac" section to learn better. In the opposite side of the circumpolar area there is another constellation, the Giraffe; but this one is not described here (see "modern constellations" below).
Cepheus & Cassiopeia: the King and his Queen. If you watch the Great Bear and travel with your eyes beyond the Polar Star, you'll find an evident "W" (or "M", depends on the period of the night/year). This is Cassiopeia, the celestial Queen. Next to the latter, a sort of "house" with a sharp roof represents her husband, Cepheus the King. Both constellations are best-visible in the Fall, and both are crossed by the Milky Way. note Technically, the Milky Way indicates only the faint stripe of light you could glimpse in the sky if you're far from a city, but is commonly used to indicate the galaxy we're living in (the Milky Way Galaxy). Here we'll use the word only in the former sense; when coping with the galaxy as a whole, we'll call it "the Galaxy", "our Galaxy" or "our own Galaxy". As is known the "milky way" is just our own Galaxy seen from inside: less-known is, the visible stripe is entirely made by the spiral "arms" of the Galaxy, while the Galaxy's central bulge is actually invisible from Earth. This because our Solar System is placed within the arms making the external disk of the Galaxy, whose dusts hide the central bulge to our vision. To be precise, the "w" of Cassiopeia portrays only the queen's throne; the drawings show the woman sit on it while looking at herself with a mirror. Like the "great plough" of the Bear, The "w" of the Queen is well-visible even from cities: as the central point of the W seems pointing toward the Polar Star, Cassiopeia cane be useful to confirm the latter's correct identification. Though fainter and harder to find in the sky, the King is the second most northern constellation after the Little Bear and contains a famous star: "Delta Cephei" (aka the "Delta" star of Cepheus). This is a "variable star" which changes its size and its brightess periodically; it has been chosen as the prototype of its own group of variable stars: the Cepheids, utilized to measure the distances of the galaxies. Cepheus also contains another famous star: Mu Cephei, the Garnet Star, named so because of its intense red color, that is one of the largest stars known with a radius more than 1400 times that of the Sun.
Northern Seasonal Constellations
These constellations are called "seasonal" because they're visible only in some seasons and not in others by North American and European watchers. They periodically rise from East and set in the West across both the night and the year, just like the Sun. Still, Northern Seasonal Constellations are more visible than the Equatorial Constellations (which are seasonal as well), to the point you can even see them at your Zenith in certain moments. Actually, if you're British or Canadian you can see some of these figures most the night/most the year like those in the previous folder. On the other hand, they are hard to spot from Australia or New Zealand. The three brightest stars of the Northern celestial Emisphere (Arcturus, Vega, and Capella) belong to northern seasonal constellations. Six constellations of the Zodiac (Pisces, Aries, Taurus, Gemini, Cancer & Leo) and six modern constellations belong to this group as well, but they are described in their own folders for convenience.
Bootes: the Herdsman. Similar to a kite in shape, Bootes the Herdsman is a large constellation visible in the Spring's night sky near the Great Bear's "tail", and is also called "the Guardian of the Bear". Bootes is easily distinguished thanks to Arcturus, the brightest star above the celestial Equator and the 4th most luminous star in the whole firmament. This is an orange "giant star" placed at the narrower end of the "kite" and marking the man's legs; his head and shoulders are signed by the other end of the kite. The diameter of Arcturus is 30 times bigger than the Sun's and emits 100 times more light than the Sun; despite this, Arcturus is still smaller than other giant stars like Betelgeuse and Rigel in Orion. In the next 5,000 million years, astronomers say our Sun'll become a giant similar to Arcturus. note Arcturus is one of the "stars of 1° magnitude." 1° magnitude-stars are the brightest star in the Sky and the first to attract our eyes when watching the night sky. They are about twenty. The North Polar Star is not among them, as well as none of the 7 main stars of the Great Bear. In the Northern Emisphere we can see Aldebaran, Altair, Arcturus, Betelgeuse, Capella, Deneb, Pollux, Procyon, Regulus, and Vega. In the Southern one there are Alpha Centauri, Beta Centauri, Achernar, Antares, Canopus, Fomalhaut, Rigel, Sirius, Spica, and two stars of the Southern Cross. The most northern portion of Bootes was once identified as a constellations on its own, the "Quadrant". From this area seemingly come the Quadrantid Meteors at the beginning of January: this is usually the richest swarm of "shooting stars" in the year, but weaker and less-famous than those seen in the 10-12 August, the Perseids (see "Perseus" further).
Lyra: the Lyre. A small but easy-to-find constellation best-visible in the Summer. Similar to a rhomboid, the Lyre portrays the eponymous ancient instrument and is definitively dominated by its alpha star: Vega, the 5th brightest star in the whole Sky. This is a light-blue star not much bigger than the Sun and relatively close to the Solar System. However, we don't know if it is surrounded by planets as shown in a famous 1970s Japanese cartoon. note Planets outside the Solar System have been discovered only since the 1990s; astronomers think only stars the size of / smaller than the Sun can be "old" enough to have had the time to form a planetary system populated by intelligent forms of Life. Vega is probably still too "young". The Lyre also contains a famous quadruple star called "the double double", and one of the most celebrated nebulas: the Ring Nebula, so-called because it appears ring-shaped when seen with a telescope. Nebulae are huge masses of gas and/or dust much larger than the whole Solar System, and are found in the external "disk" of our Galaxy. There are several types of nebulas; the Ring Nebula pertain to the subgroup called "planetary nebulas" (see also the Zodiac section).
Auriga: the Coachman. At the opposite side in the North Sky, Auriga the Coachman is an evident Winter constellation actually portraying more a shepherd than a coachman. Its main star, Capella, is the 6th brightest star in the Sky and could be seen almost all year-round from Canada. It's a yellow giant star similar to Arcturus, and makes one of the corners of the irregular pentagon of Auriga (the pentagon signs the man's body). Capella means "little goat": indeed, it marks a goat above the man's shoulders. Curiously, one of the stars of the "pentagon" is at the same time one of the Bull's horns, so Auriga and Taurus actually appear like one single figure in the sky. Which constellation this star pertains to has long been controversial; however, since 1922 it has been assigned to Taurus. Crossed by the Milky Way, Auriga contains several Star Clusters: more precisely, Open Star Clusters. note Star clusters are made of stars really close to each other in the Space. There are two very different types of star clusters: Open Clusters and Globular Clusters. Open Clusters are made of a relatively low number of young stars born together from the same nebula, and are usually near the Milky Way. The most famous open cluster is the Pleiades, in Taurus. For globular clusters, see just below.
Hercules: the Knelt Man. The second largest constellation above the sky Equator after the Great Bear, Hercules would be visible between Arcturus and Vega in the summer sky, but its stars are all rather weak and the vast figure is not easy to see from cities. Represents the famous Greek hero in a kneeled pose, with one foot near the Dragon's head; several other ancient constellations are somehow linked to the hefty man by some legends. Hercules' head is marked by a "red giant" star, while his body is partially signed by a quadrilater of stars just in the middle of his figure, nicknamed "the Keystone". In one side of the Keystone there is a famous deep-sky object: note Deep-Sky Objects are nebulae, galaxies & star-clusters considered together. In other words: if it's neither a proper star nor a body of our Solar System, then is a deep-sky object. "M13", the greatest "globular cluster" in the Northern Sky. note Globular Clusters are huge spherical clusters containing millions of stars. They have nothing to do with the much smaller "open" star clusters: the globulars are outside the disk of our Galaxy, encircling it together like an imaginary sphere called "the Galaxy's Halo". Also note the stars of a Globular Cluster are much more ancient than those of the Open Clusters. Deep-sky objects have their own terminology; the most important ones are listed in the Messier Catalogue or M-Catalogue, which contains about 110 objects from the whole firmament. M13 is the 13th object in the list. Finally, one curiosity: our Solar System is travelling in the space toward the celestial area occupied by Hercules.
Cygnus: the Swan. Maybe one of the most beloved constellations by night-sky fans. Cygnus the Swan is rightly nicknamed the "Northern Cross": its five main stars really make a figure like a Latin cross. Cygnus is better-visible in Summer (near the Lyre), and its cross is by far bigger than the famous Southern Cross. The Swan is shown in flight: the longest arm of the cross is its neck, the lateral arms its open wings. Both the head and the tail of the Swan are marked by a famous star. Deneb (literally "the tail") is a bright bluish star, one of the most powerful "giant stars" in the sky emitting 100,000 times more light than the Sun; but it's 3,000 light years from us, and so appears less luminous than other smaller but closer stars like Vega or Sirius. The head is signed by Albireo, maybe the most admired double-star in the sky: its members are one blue and the other orange, making a beautiful contrast if seen with a telescope. Also worthy of note are "61 Cygni A" and "61 Cygni B", a couple of "dwarf" orange-stars close to the Sun whose distance from us was the first among stars to be measured. Cygnus also contains a characteristic trait of the Milky Way, and several Deep-Sky Objects. One of them is a nebula whose shape resembles so North America it's commonly called the "North America Nebula". In the NGC catalogue it's the 7,000th member. note NGC is the most complete catalogue of deep-sky objects, with almost 8,000 nebulae, star clusters, and galaxies from the whole Sky. They are listed with the sigle NGC followed by a number: the North America Nebula, for example, is NGC 7000. Every object in the Messier Catalogue has also its NGC number. Another nebula is called the Veil Nebula for its delicate look, but is actually the remain of an extremely violent event: a Super-Nova, aka the explosion of a giant star. And then, there is one of the most-known examples of a possible Black Hole: Cygnus X-1. For obvious reasons the supposed black hole is invisible from Earth, but the matter around it emits X-rays detectable with apposite instruments —- hence its name, Cygnus X-1.
Pegasus & Andromeda: the Winged Horse and the Chained Woman. The names of these two constellations are rather familiar though for different reasons. Like Auriga & Taurus above their stars actually make one single figure in the sky, and one star appears shared by both. Modern astronomers, however, assign this star to Andromeda. Despite their lacking of 1° magnitude stars, Pegasus and Andromeda make together the brightest figure of the Northern Fall. Pegasus portrays the famous flying horse with bird-like wings, and is the third biggest constellation entirely in the sky's northern emisphere. Its most evident feature is the so-called "Great Square" (actually a rectangle) of stars signing the animal's body. note But only three really belong to the Horse; the forth one marks also the Woman's head, and is the disputed star today attributed to Andromeda.. The horse's head and forelegs are marked by other stars, while the hindquarters curiously are not shown in drawings. Andromeda is basically a curved "tail" of stars (with other weaker stars around) protruding from the Great Pegasus' Square; it portrays the woman chained against a rock (see Perseus to understand why). The fame of Andromeda is strictly linked to one single deep-sky object: the Great Andromeda's Galaxy, also called "The Andromeda Galaxy" or simply "Andromeda". This is the biggest galaxy within our Local Group of galaxies, a bit larger than our own Galaxy but very similar to the latter: both share the classic spiral shape and both have two smaller "dwarf galaxies" nearby. In the Messier Catalogue the Andromeda Galaxy is the 31st object (M31) and is the more distant celestial object still visible with naked eyes: 2,000,000 light-years from us.
Perseus: the Greek Hero. Ancient constellations are often linked to each other by mythology. Perseus, for example, was the Greek Hero who killed Medusa — the monster which had snakes instead of hair and which turned into stone everybody watched it. After killing Medusa, Perseus saved the princess Andromeda from another critter, the sea-monster Cetus (portrayed in an equatorial constellation). During his flight on the winged horse Pegasus, Perseus saw Andromeda chained on a rock as a sacrifice to calm Poseidon' anger down. Andromeda in turn was the daughter of King Cepheus and Queen Cassiopeia note It was just Cassiopeia's vanity that provoked the God's anger., and finally got married with Perseus. All these characters are portrayed near each other in the northern Autumn Sky. Perseus has the shape of a curved "Y", and shows the hero holding the Medusa's cut-off head with one hand. Medusa's eye is marked by one of the most famous variable stars: Algol (meaning the "devil"). Algol actually do not vary its size: it is a double star whose members eclipse each other every three days — just like the Moon does sometimes with the Sun. At every eclipse, Algol's overall brightness decreases. Perseus contains another "double" object as well, the "double cluster". Finally, Perseus is the apparent source from which the popular 10-12 August "shooting stars" come from — the Perseids indeed. note Shooting stars are definitively NOT stars. More properly called Meteors, they are simple grains of dust belonging to our own Solar System. When the Earth crosses the orbit of some comets, the grains of dust within the comet-orbit enter massively our atmosphere, making the familiar luminous trails. If you watch carefully a swarm of meteors, you'll note they seem all coming from one single point within a precise constellation. In the case of the 10-12 August ones, this is Perseus.
Lesser northern constellations. The constellations above vary in size from medium to very large, and are usually well-visible. However, most of the 88 celestial constellations are smaller/weaker than them and get usually unseen by occasional observers. Among the "lesser constellations" above the celestial Equator, some were created in the 1600/1700 centuries while others come from the Ancient Greek times. Here we list only the latter. note All the constellations invented in the Modern Age are grouped in the last folder of this page for convenience. Despite their faintness, many effectively resemble the portrayed figure: Corona Borealis the Northern Crown can effectively recall the shape of a small crown between the Herdsman and Hercules, even with one star brighter than the others which is compared with a gem of the crown. In the opposite portion of the North Sky there's the aptly-named Triangulum the Triangle, a small triangle of stars near Andromeda and the Ram. Like Andromeda, it contains an important spiral galaxy: the "Triangulum Galaxy", the third largest member of our Local Group of galaxies after the Andromeda Galaxy and our own Galaxy, but fainter than Andromeda and not-visible with naked eyes. Interestingly, both Corona Borealis and Triangulum have one counterpart constellation in the Southern Emisphere. Between the Swan, the Winged-Horse, and the Eagle (see "equatorial constellations") you could glimpse three tiny constellations: Sagitta the Arrow, Delphinus the Dolphin, and Equuleus the Little Horse — at least, the first two: Equuleus is so faint even skilled watchers have difficult to spot it. Sagitta (not to be confounded with Sagittarius which is below the Equator!) resembles perfectly the shape of an Arrow, while the Dolphin recalls the eponymous figure only vaguely; the rhombus of stars signing the animal's head is curiously called the Job's Coffin. The Little Horse (or the Colt) is the smallest Northern constellation and the second smallest in the whole sky; it's just a tiny group of starlets signing the animal's head only, and placed just near the head of the other more famous celestial horse, Pegasus.
These constellations are crossed by the celestial Equator. Their placement in the Sky make them equally visible from the Northern and from the Southern emisphere of the Earth; compensating this, for the americans and the europeans they appear always lower in the sky-dome than the Northern Constellations. If you want to see them near the Zenith you have to go near the terrestrial Equator. If you travel even souther you'll see these constellations inverted. Just as an example, Orion the Hunter and Ophiuchus the Snake-Carrier are two human figures which appear upright from U.S. latitudes, but the Australians actually see them like they are falling head-first from the sky! Some constellations of the Zodiac (notably Virgo) and two modern constellations are also crossed by the Equator, but here we'll only talk about ancient non-zodiac constellations. As a whole equatorial constellations include some of the biggest constellations in the sky, but they usually are relatively poor of bright stars; the great exception is Orion.
Orion: the Hunter. Orion is almost-universally quoted as "the King of the Constellations". Its seven brightest stars make together an great upright rectangle with a line of three very-close-to-each-other stars inside the rectangle itself. This coffeepot-like figure is unmistakeable and perfectly-visible worldwide even from the most light-polluted cities. Increasing its beauty even more, the Hunter is the only constellation portraying a human character that can actually recall a human figure. Finally, Orion has a plenty of interesting stars and deep-sky objects: some of them are a staple in astronomy books and magazines, to the point you aren't considered a true night-sky lover if you've never watched Orion at least once with your binoculars or your small telescope.
If you live in the Earth's Northern Emisphere Orion is a winter constellation. Even though is called "the Hunter", its portrayal looks more like a warrior seen from the front. Orion is shown lifting a mace and a shield (both signed by faint stars) to defend himself against the charging Bull nearby, and has also a sword hanging from his belt. The belt is signed by the aforementioned three central stars, and is just on the celestial equator; the shoulders and the feet are symmetrically placed above and below the equator, and are signed by the stars of the "rectangle". Orion's right shoulder and his left foot are marked by two of the brightest stars in the Sky: Betelgeuse & Rigel, note Both are Arabic words meaning shoulder and foot respectively. both hundreds of light-years far from us. Rigel has the letter "Beta" and thus should be less-luminous than Betelgeuse (the "Alpha" star); actually Rigel is brighter than Betelgeuse, and the 7th brightest in the whole firmament. note However, note that Betelgeuse slightly changes its luminosity periodically, and can be the brightest star in certain moments.. Making their constellation even more attractive, the two stars have contrasting colors: Rigel is blue, Betelgeuse is red. Both belong to the "super-giant stars" category, being even bigger than "simply-giants" like Arcturus. Rigel's diameter is 90 times greater than the Sun's; if placed at the center of the Solar System, Rigel would swallow Mercury in its orbit. But even Rigel is a tennis-table ball when compared with Betelgeuse. This star has a diameter 600 times greater than the Sun, and is one of the biggest stars in the whole Galaxy; if put in the place of the Sun, Betelgeuse would swallow the whole Inner Solar-System — Mercury, Venus, Earth, Mars, the Asteroid Belt, and maybe even Jupiter! In other world, Betelgeuse could contain 10,000,000 Suns inside it. note Remember that the Sun could contain about 10,000 Earths, giving an effective idea about how immense the stars can be. Astonishingly, Betelgeuse's total mass is only 50-80 times the Sun. This means its density is extremely low: an amount of Betelgeuse's matter as big as a house would weigh like a sand-grain on Earth. Moreover, being a red star, the surface of Betelgeuse is colder than the yellow Sun and much colder than the blue Rigel. Despite its smaller diameter, Rigel has about the same total mass of Betelgeuse and produces even more light than the latter; one day Rigel will become a red super-giant the size of Betelgeuse. Both Rigel and Betelgeuse are super-massive stars at the end of their life, with Betelgeuse in a more-advanced phase than Rigel. When born with a mass much bigger than the Sun, stars only live few million years (Rigel & Betelgeuse were still non-existing when the dinosaurs populated the Earth!). After ending their internal "fuel" of hydrogen they become enormously inflated, and finally explode with unimaginable violence (the Supernova). All what remains from the former super-giant is a "pulsar" or even a Black Hole. note To learn more, see Taurus in the Zodiac section and the Useful Notes about Black Holes.
Betelgeuse and Rigel are not the only stars in Orion; there are also two nebulas which are perhaps the most famous nebulas in the Sky together with the "Crab Nebula": the Great Orion's Nebula and the Horsehead Nebula. The first is a bright "diffused nebula" visible to the naked eye like a "spot" in the middle of the line of stars marking the Hunter's sword. Nebulas like this are a bit like pregnant women: new stars are continuously born from their gas. M42 (The Great Nebula's official name in the M-Catalogue) has at its center a foursome of stars called Trapezium for its trapezoidal shape; they are "newborn" stars recently originated from the nebula's gas. The Horsehead nebula (which, for some reason, is not even in the NGC catalogue!) is a dark nebula whose shape effectively recalls the Chess horse; it is near the Orion's belts, but sadly it's visible only with large telescopes. While bright nebulas are made mainly of hydrogen (the simplest and most abundant element in the Universe), dark nebulas are often full of complex substances, even including some organic compounds.
Canis Major & Canis Minor: the Great and the Little Dog.note These two constellations actually are slightly above (C. Minor) and slightly below (C. Major) the Equator, but are here for convenience. Yes, there aren't only the Great and the Little Bear in the Sky; and yet, Canis Major and Canis Minor are not the only dogs in the sky (see "Modern constellations"). Both are small but bright constellations just beside Orion the Hunter, and represent his hunting dogs. The Little Dog is among the smallest constellations, looking like a simple small segment of two stars beside Betelgeuse; one of these two stars, Procyon, is the 8th brightest star in the firmament. The Great Dog (or more simply, "the Dog" par excellence) has a polygonal shape, but it too resembles anything but a dog; its many bright stars make it one of the brightest constellations, just as bright as Orion itself. But the Great Dog's fame is due only ot its Alpha star: Sirius, the "Dog Star". This is by far the brightest star in the entire firmament, note Not counting Venus and Jupiter (which are actually planets) and of course the Sun, which IS definitively a star. but owes its record only because is one of the closest stars to us (merely 8.6 light years); actually Sirius is only a bit bigger than our Sun. Procyon too is a very close star (11.4 light years from us). The two dogs' alpha-stars incidentally share several features. Like the Sun both are in the middle of their life, but one day they'll enter the realm of the Giant Stars (not Super-Giants: their mass is too small). But today, Sun, Sirius, and Procyon are still in what astronomers call the "Main Sequence" of the Hertzsprung-Russell Diagram. Most the other stars in the sky belong to the Main Sequence — the giant and supergiant stars are above the latter. Telescopes have revealed another astounding analogy between Sirius and Procyon. Both have a "White Dwarf Star" which orbits around them: "Sirius B" and "Procyon B". White Dwarfs are by far the smallest true stars in the Galaxy. Their diameter can be 100 times smaller than the Sun, and 100,000 times smaller than that of a red super-giant star like Betelgeuse: some white dwarfs are not bigger than Earth itself! Making the exact contrary of Betelgeuse, white dwarfs are extremely dense: one handful of a White Dwarf's matter will weigh several tons on Earth. A White Dwarf is the tiny remain of what once was a star similar to the Sun or to Sirius. According to the astronomers, the latter will one day become white dwarfs when beyond the "giant" phase.
Serpens & Ophiuchus: the Snake and its Carrier. Serpens the Snake is unique among all the 88 constellations. It's the only one to be divided in two distinct parts: Serpens Caput (the snake's head) and Serpens Cauda (the snake's tail). This makes the areas of the Sky being actually 89. The Snake's middle body is actually included in Ophiuchus the Snake-Carrier, which is between the head and the tail of Serpens. Together the two constellations portray one single figure — a man grasping with his hands a huge snake which is in turn coiled around the human's waist. Though made of faint stars, Serpens contains a nebula (the "Eagle Nebula") which has become famous after a spectacular photo made by the orbiting Hubble Space Telescope in the 1990s. Ophiuchus, too, is very peculiar among constellations. Being briefly crossed by the Sun at the first half of December, it should be considered the 13th constellation of the Zodiac; but it is not traditionally considered so in culture. Ancient astronomers might have overlooked Ophiuchus because the Ecliptic fairly "touches" only one of his feet (see the Zodiac below). Ophiuchus is a vast Summer constellation (Winter for Australians) at the exactly opposite end of the Celestial Sphere with regard to Orion, but like every other non-Orion constellation, its irregular figure recalls anything but a human. The ophiuchus' head is just near Hercules' head, but the former's body goes southwards, the latter's goes northwards. Being crossed by the Milky Way, Ophiuchus has a plenty of nebulas and star-clusters. Curiously, one of the ophiuchus' most famous stars is invisible to a naked eye: the Barnard's Star, the second closest star to our Sun after the Alpha Centauri system. It's a "red dwarf" star, and its dwarfness explains why you need a telescope to see it despite its closeness to us. note "Red dwarfs" are much smaller and weaker than a yellow star like the Sun, but still much bigger than the tiny "white dwarfs". Actually, red and white dwarfs are very different things. Like the Sun, the red dwarfs belong to the Main Sequence of the Hertzprung-Russell Diagram; they simply have less "fuel" than the other Main-Sequence stars, and are destined to live much longer — even a hundred of time longer than the Sun. On the other hand, White Dwarfs are below the Main Sequence and are more the remains of a former star rather than true stars. The Barnard's Star has possibly a planetary system around, and appears moving faster in the Sky than every other star. note Stars are not fixed in the Celestial Sphere as commonly thought: they change their position throughout the years. But this movement in almost-always undetectable to a naked eye: ancient people actually saw the stars almost in the same position they have today. On the other hand, the Barnard's Star appears "travelling" among the other stars, changing visually its position every year. This is also due to a perspective effect: if two stars travel the same speed in the space, the nearest ones appear speedier than the other. Another star which has notably changed its position through the centuries is, curiously, the bright Arcturus in Bootes.
Aquila: the Eagle. The "King of the Birds" should not miss in the Sky. Aquila is an equatorial constellation near Ophiuchus, and is visible not far from the Swan. Like the latter it is shown in flight and has the shape of a cross but smaller, more irregular, and with the arms of the same length (a "greek cross"). The Eagle's alpha star, Altair, is one of the three corners of the famous "Summer Triangle" (Winter for southerners), together with Vega in the Lyre and Deneb in the Swan. These three stars are all bluish in color, but Altair is easily recognizable because is lined by two starlets and is less-close to the other two. Like Vega and unlike Deneb, Altair is a star of the "Main Sequence" relatively close to us. If you're lucky, you might also find a Nova-Star in Aquila. note "Novae" (literally "new") are usually-invisible stars that occasionally become visible to the naked eye. Even though the result of an explosion as well, Novae have nothing to do with the more famous and drammatic Super-novae: "nova" stars do not disintegrate totally after the explosion, and can explode more than once. Many "novae" are double-stars that are so close to each other, one of them literally "sucks" some matter from the other! Surprisingly, the "vampyre" star can be the smallest one; if so, it's because is a super-dense "white dwarf" sucking from another less-dense star. Sometimes the dwarf star expels abruptly the sucked matter, suddenly increasing its overall luminosity: this is perceived from Earth as a "new star" in the Sky (the Nova, indeed).
Cetus: the Whale. From a flying creature to a swimming one. As one can expect from its name the Whale is one of the biggest constellations (4° placement), but its portrayals resemble anything but a whale. Cetus means "sea monster", and is actually a sorta sea-dragon with human-like forelimbs and fish-like tail. Like most fall constellations (spring for southerners), the Whale is weak and difficult to find; it's basically a couple of irregular pentagons linked with a middle line of stars across the Equator. One star of the "line" is one of the most famed variable stars: "Mira Ceti" (or more simply Mira, meaning "the wonderful one" in Latin). This is a red giant which greatly fluctuates its size and luminosity every 11 months: at its minimum Mira is not even visible to the naked eye, while at its maximum is among the brightest stars in the constellation. The Whale also contains the most similar to the Sun among the nearest stars, and this status makes it interesting for the famous SETI Research Project (searching for extraterrestrial forms of life).
Hydra: the Sea Snake. Some vast constellations appear like a very long line of faint stars meandering among other more solid figures, often with a group of stars which mark one end of the line. Draco is a good example near the North Pole; others are Pisces and Serpens. However, the two Up to Eleven examples are better-visible from the southern emisphere: Eridanus the River (see further) and Hydra the Sea-Snake. note Also called with the weird name "the Female Sea-Snake" to distinguish it from the much humbler Hydrus, the "male" sea-snake near the South Pole. Theoretically, Hydra should be the mythical seven-headed monster defeated by Hercules during one of his 12 fatigues, but is always portrayed as an one-headed snake. Although less-known than other celestial figures because of its indistinct appearence, the Sea-Snake detains the special record of the largest by area among all 88 constellations in the Sky. Its head is marked by a small bunch of stars near the Crab just above the celestial Equator; the remaining body is below the equator, travelling between Leo/Virgo and the Centaur and ending near the Scales. Though mainly visible in the northern Spring, the Sea-Snake's head is still visible in Winter and its tail already in Summer, giving an idea about its extreme length.
The 12 Constellations of the Zodiac
These are the constellations crossed by the Sun across the year (not counting Ophiuchus). You have already known their names since your childhood. But do you know their shape, and have you ever recognized "your" constellation in the Real Life Sky? Difficult things. Sadly, we Western people have lost the habit to watch the night sky, even for simple amusement. Moreover, like every other constellation, the Zodiac ones are not fixed in the sky but turn above our heads across the night and the year. Worsening things, all constellations of the Zodiac are seasonal. (Remember? Seasonal constellations rise and set in a night, and are visible only in some seasons of the year.)
The 12 constellations of the Zodiac make together a "ring" around the Celestial Sphere, and each is like one link of a circular chain. They are placed the Sky with the same order we learnt when we're children: Aries the Ram, Taurus the Bull, Gemini the Twins, Cancer the Crab, Leo the Lion, Virgo the Virgin, Libra the Scales, Scorpius note NOT Scorpio: this term is used only in Astrology. the Scorpion, Sagittarius the Archer, Capricornus note NOT Capricorn: this term is used only in Astrology. the Sea-Goat, Aquarius the Water-Carrier, and Pisces the Fish. However, they actually do not start with Aries and end with Pisces; like a ring-shaped chain the Zodiac has not a "start" and a "end", and you can alternatively read its constellations in the opposite direction. In the list below we don't follow rigidly the classical order because is more convenient so.
Technically, the Zodiac is the celestial area surrounding the Ecliptic. note Remember? the Ecliptic is the the circular route covered by the Sun during its apparent yearly "trip" in the firmament — needless to say, it's the Earth that actually turns around the Sun. The Moon and the Planets of the Solar System are always near the Ecliptic, almost-always appearing in one of the 12 Zodiac constellations (and Ophiuchus). Even though planets resemble bright stars of these constellations, if you keep well in mind the shape of the constellations you'll easily note the planet as an "intruding" star. The Ecliptic crosses the Sky's Equator in two points called Equinoxes, going half-above and half-below the equator but never far from the equator itself. Thus, all the Zodiac constellations are in turn near the Equator. Pisces, Aries, Taurus, Gemini, Cancer & Leo are (totally or almost-totally) in the northern celestial emisphere, and are better-visible from USA and Europe; Libra, Scorpius, Sagittarius, Capricornus & Aquarius are (totally or almost-totally) in the southern one, and are better-visible from Australia or South Africa. Virgo is the only truly Equatorial constellation of the Zodiac, equally visible from both the emispheres.
Keep this in mind: when the Sun appears in one constellation of the Zodiac, the constellation at the extreme opposite of the Sky Sphere is the best-visible in the night sky of that period. For example, when the Sun is in Gemini, the best-visible zodiac constellation in the night is Sagittarius; when in Sagittarius, is Gemini and so on. For American observers, the Bull and the Twins are winter figures; the Lion and the Virgin are spring figures; the Scorpion and the Archer summer figures; the Water-Carrier and the Fish fall figures. The Ram is best-visible between Fall and Winter, the Crab between Winter and Spring, the Scales between Spring and Summer, the Capricorn between Summer and Fall. Not all constellations of the Zodiac are the same brightness however: Taurus, Gemini, Leo, Virgo, Scorpius & Sagittarius are the most easily-visible. Except for Sagittarius, each of them has one luminous star of 1° magnitude (but none of these stars is among the 10 brightest stars in the Sky). The other zodiac constellations are faint (although some have a very large area), and are hard or even impossible to spot from cities.
Indeed, zodiac constellations are NOT the same size, and the Sun do not stay exactly one month in each like in the astrological Zodiac. For example, Virgo holds the Sun nearly two months, while Scorpius only few days. And they DO NOT correspond to the periods you see in the calendar... unless you're 2,000 years old! Because of the notorious Precession, when you came to light under a "sign" of the Zodiac the Sun actually had good chances to be in the former constellation. If you were born under Virgo, the Sun was probably in Leo; if under Pisces, it was more likely in Aquarius and so on. And if you're so lucky to be born under Sagittarius... arguably the Sun was in Ophiuchus the Snake-Carrier!
Taurus: the Seven Sisters and the Crab Nebula. Astronomy-lovers consider Taurus one of the most interesting constellations of the Zodiac and of the whole night-sky; it contains several remarkable objects for the owners of a pair of binoculars or a small telescope. Visible in the northern Winter near Orion, the Bull has the shape of a large "V" representing the animal's horned head (the two branches of the V are the horns of course), with fainter stars signing its forebody. Like Pegasus, the bull's hindquarters are not shown in drawings. The Bull's eye is marked by Aldebaran, an orange-giant star similar but less-luminous than Arcturus. Near Aldebaran there are the stars called Hyades. The Hyades is the Open Star Cluster closest to us in the Sky (150 light-years of distance); its closeness makes it easily-distinguishable with naked eyes, looking like a small "v" of about 12 stars (you'll see much more stars with binoculars) signing the head of the bovine. Like most other "open clusters" the Hyades formed in the space only few million years ago; even though appearing near the hyades, Aldebaran is actually closer to the Sun and doesn't belong of them.
In spite of being one of the most appreciated open-clusters in the sky, the Hyades get easily overshadowed by another, even more famous star-cluster of the Bull: M45, the Pleiades, also known as "the Seven Sisters". Even laypeople often know or have heard about "the pleiades", but many think they're a constellation on its own: actually the pleiades are inside the constellation Taurus — however, as they're placed apart from the main figure of the bull, they appear like something distinct. note The Pleiades occupy a smaller portion of the sky than the Hyades, and if you're an occasional observer you'll probably see only a confuse spot instead of distinct stars. More expert observers can see seven stars with their naked eyes (hence the ancient name "the Seven Sisters"), but some sharp-eyed people can see other stars as well. Binoculars reveal the Pleiades being actually hundreds. The Pleiades are even younger stars than the Hyades: they appeared merely 100,000 years ago — after the mammoths and the cavemen! All the stars of the Pleiades were born together from the same nebula, and are still partially-surrounded by the nebula which originated them. Another famous "star" (better, a proto-star) in the Bull is "T Tauri", the prototype of those stars which are still in formation within their nebulas.
Taurus contains another singular object. This one is even more recent than the Pleiades, appeared in the sky in full Human History: M1, the Crab Nebula, the first object in the Messier's list, and definitively one of the most portrayed celestial objects in astronomy books and magazines today. Ironically, the "crab nebula" is invisible to a naked eye and its shape actually recalls anything but a crab. M1 is the most well-known example of a remain of Supernova. As said above Supernovas are super-giant stars exploding in the space. note Some scientists formerly thought a Supernova could have been the cause of the Dinosaur Extincton 65 million years ago. Its radiations would have reached the Earth provoking genetic mutations in the living beings, exterminating them and finally leading dinosaurs to their extinction. However, there is not proof about all this, and this theory is now discarded in favor of the asteroid/comet impact one. See also here. The astonishing this is, when the explosion happens the star emits such an immense amount of light it can even outbright its own whole galaxy! If a Supernova explodes within our Galaxy, it can appear so luminous in our sky to project shadows (just like it was another Moon). This is what really happened in year 1054, when Chinese and Native-American observers reported an entirely "new" star of extreme brightness in the sky; it was indeed what modern astronomers call a Supernova (literally "super-new"). note Some sources say it became as bright as the Sun, but this is unlikely. Oddily, European observers of the Medieval Age didn't report the event. If it was really like a second Sun, it would not get unnoticed to medieval people! If we are living before 1054 we'd not see the Crab Nebula, but its original star instead. Today, what remains from the former super-giant star is the nebula itself (whose gas is constantly dispersing in the space and will become invisible in the future), and a strange object inside it, infinitively smaller than the original star but even more impressive than a White Dwarf: a Pulsar, also called "neutron star". note To be precise, the Pulsar is not a proper star but a middle-way between a White-Dwarf Star and a Black-Hole. It's much smaller than the Earth itself but even more dense than a "white dwarf". Here the matter is not made of the usual atoms but only of an extremely-concentrated mass of Neutrons — hence "neutron star". The pulsar spin more times per second like a spinning-top, and emit at each turn a burst of X-rays and Gamma-rays detectable from Earth like a lighthouse — hence "Pulsar", which is a Portmanteau of "Puls(ating) (st)ar". Many other Pulsars are known in our Galaxy, always originated from a Super-Nova: for example the one of the Veil Nebula in the Swan, and "Cassiopeia A" in the Queen. The latest one is the remain of the last supernova exploded in our Galaxy (1500 century), but the event was only barely seen to the naked eye.
Gemini: Castor & Pollux. Together with Taurus, Gemini is the most northern constellation of the Zodiac, and is close to Orion as well. A well-visible invernal figure for northern observers, the Twins deserves its name rather well. Its two main stars are very close to each other in the sky, each signing one of the twins' heads: their names are the same of their respective twin, Castor & Pollux. The twins' bodies are made by two parallel lines of stars direct toward Orion. Even though appearing almost identical, Castor and Pollux are actually very different stars. Pollux is a "yellow giant" star similar but less-bright than Capella (in the near Auriga); Castor is a complex multiple star with six members. Even tough slightly fainter than Pollux, Castor is the Gemini's Alpha Star — Pollux is only the Beta. Gemini contains among the Deep-Sky Objects a planetary-nebula called "the Eskimo Nebula" because it resembles the head of a man with a hood in some photos. Interestingly, both the true planet Uranus and the "dwarf-planet" Pluto were first discovered in Gemini. note Planets from Mercury to Saturn are visible with naked eyes and thus have been known since the Antiquity. Uranus Neptune & Pluto are only-visible with binoculars or telescopes, and were respectively discovered in the 1700, 1800, and 1900 century.
Leo: the King and his Sickle. This is considered one of the most easily-recognizable constellations of the Zodiac. Between the Great Bear and the Equator, Leo is a large and bright figure that has effectively the shape of a leg-less lion (the legs are signed by fainter stars below the main figure), even with a distinguishable "mane". note One can alternatively see the Lion as an egyptian Sphynx.. The front portion of the animal is marked by an inverted question-mark popularly-known as "The Sickle" for its shape. The "dot" of the "?" is the bluish 1° magnitude star Regulus (meaning "the little king") note Interesting that Regulus can sometimes be eclipsed by planets of our Solar System, as the Ecliptic passes very close to the star.; the mane is signed by the remaining Sickle. The lion's hindquarters are marked by a triangle of stars. Like the Great Bear the Lion has many galaxies visible with small telescopes, although not so many as in the Virgin (see below). From Leo comes an unusual meteoric swarm each november, the Leonids; they are usually few, but each 33 years they become the brightest and most abundant "shooting stars" in the Sky, even more than the Perseids and the Quadrantids themselves. The last time this happened was in year 1999.
Virgo: Triumph of Galaxies. Virgo is the giant of the Zodiac constellations, and actually the second biggest constellation in the whole sky after the near Hydra. Being more extended in "latitude" than in "longitude", the Sun employs almost two months to cross the area of Virgo — more time than every other zodiac constellation. Moreover, the equator and the Ecliptic encounter each other just in the Virgin, which contains thus one of the two Equinoxes. However, apart from its alpha star Spica (literally the "ear of wheat" on one virgin's hand), the constellation is not particularly bright. You can see it below the Herdsman and the Lion during the northern Spring (the southern Fall), and like almost every human figure it resembles anything but a woman. It recalls better a wide "Y" surrounded by other stars, with Spica marking one of the ends of the "Y" just below the Equator. Spica is one of the bluest and hottest 1° magnitude stars; though much bigger than the Sun it's still in the "main sequence" and not a proper giant star like Rigel or Deneb. However, the main interest of the Virgin are its galaxies. No other constellation in the sky has so many galaxies visible with small telescopes. Most of them pertain to the "Virgin Cluster" of galaxies, 50,000,000 light-years far from us. This group of galaxies is much larger than our small "Local Group"; while the latter has only two dozen of members (all "dwarf galaxies" except for our Galaxy, Andromeda and the Triangle Galaxy), the Virgin Cluster contains thousands of galaxies — to the point it is attracting our Local Group with its gravity. The most famous member of the Virgin Cluster is M87, an "elliptic giant" galaxy. note Not all galaxies are spiral-shaped: several haven't got the "arms" but only the central bulge, and are called "elliptical" (even though many are actually spherical). M87 is one of them and one of biggest known galaxies. The most popular Virgin galaxy is outside the cluster: the Sombrero Galaxy. This is a lonely spiral galaxy 30,000,000 light-years from us; since it's seen from the side, its shape really recalls a hat in photos. Finally, Virgo contains the brightest Quasar of the sky. note Like "Pulsar", Quasar is a Portmanteau; it means Quasi-Star. Quasars look like simple stars at the telescope, and are invisible to a naked eye. They are emit powerful radiations however, and their complete name is "Quasi-Star-Radio-Sources". Despite their modest appearence Quasars are very astounding objects. They are extremely distant galaxies (even 10,000,000,000 light years from us), and the farthest known objects in the Universe. As we see them like they were 10,000,000,000 years ago, they are actually galaxies seen at their first stages of life of the Universe, few billions years after the famous Big Bang. We don't know what exists (if it exists) beyond the quasars.
Sagittarius: a teapot near our Galaxy's center. Together with Scorpius, Sagittarius is the most southern constellation of the Zodiac — to the point that their "lowest" portions couldn't even rise above the horizon at some latitudes of the USA. The Archer would be visible below Aquila and Ophiuchus in the northern Summer, and is the third largest constellation completely below the celestial Equator. Even though representing a centaur with bow and arrows, it shouldn't be confused with Centaurus "THE centaur", which is a distinct constellation even bigger and more southern than the Archer. Like most constellations Sagittarius resembles the portrayed creature very little; however, its brightest stars form the unmistakeable profile of a teapot — to the point the constellation itself is popularly-known as the Teapot. However, its Alpha and Beta stars are outside the "teapot" figure and, oddly, are much fainter than many other stars of the Archer. Sagittarius detains the record of the constellation with more Messier-Catalogue objects. Two famous nebulae are M8 the Lagoon Nebula (a lagoon-like dark stripe apparently divides it in two), and M20 the Triphid Nebula (triphid = divided in three parts), but the Archer contains several other nebulas and star-clusters as well.
This constellation holds another even more special privilege among constellations: the exact center of our Galaxy is just in the direction of Sagittarius. note To be fair it's actually between Sagittarius, Scorpius, and Ophiuchus, but it lays just within the Sagittarius' borders. Sadly, we cannot see it with our eyes or even with the most powerful telescopes; it is masked by the dusts of the Milky Way, which is particularly bright and dense in Sagittarius. However, radiotelescopes can detect the radio-waves coming from the deepest core of the Galaxy. This core is probably a gigantic but almost-inactive Black Hole whose immense gravity allows the galaxy around to remain intact in the Space. Arguably, most other galaxies have a huge black-hole at their center and are subject to similar mechanisms. note Since we're here, let's give you some useful notes about the overall structure of the our own Galaxy. It contains about 1000,000,000,000 stars and its diameter is about 100,000 light-years, but the thickness of the external disk is "only" 1,000 light years. Our Solar System is immersed in the external disk, in the 2/3 of the Galaxy's ray from the core to the external edge (about 30,000 light-years from the Galaxy's Center). Giving an idea about the immense vastity of the galaxies: if the orbit of the Solar System's most external planet has the diameter of a coin, our Galaxy would be as wide as North-America! In a Spiral Galaxy like the Milky Way Galaxy or M31 in Andromeda, stars are continuously born from the "clouds" of gas and dust filling the external Disk. In the latter, there are not only stars (giants or dwarfs, single or multiple, with or without planets), but also many stars clusters (the "open clusters" , NOT the globular ones), many nebulae (either bright or dark, included the "planetary nebulas" and the Supernova remains), and several Pulsars and Black Holes (the so-called "degenerated stars" or "remains of star"). All these objects make together the traditionally-called "1° Population" of the Galaxy. Our Sun and all the other stars visible with naked eyes from Earth are in the Galaxy's disk and belong to the 1° Population. However, they don't remain in the disk forever; they slowly travel toward the central bulge, turning around the latter at different speed according to their distance from the Center (we're talking about million years). This kind of rotation causes the "spiral" appearence our Galaxy when seen from outside. According to traditional study the Milky Way Galaxy has four spiral "arms": the Perseus arm, the Orion arm, the Sagittarius arm, and the Cygnus arm. If so, our Solar System probably is between the Perseus and the Orion arm. Spaces between the "arms" are not empty of stars: the stars here are simply less-bright. About the central bulge, it has an elliptical shape; unlike the external disk it is poor of gas/dusty clouds, and is populated by ancient red/yellow stars which make the so-called "2° Population" of stars in the Galaxy. If you carefully watch a photo of a spiral galaxy like Andromeda you'll see that the bulge is yellowish while the external disk is bluish; actually the stars of the disk are of all colors from blue to white to yellow to red, but the blue ones are the most luminous and give their color to the disk their are in. Completing this brief description, the whole Galaxy is surrounded by about a hundred of Globular Clusters —- see Hercules in "northern seasonal constellations"..
Scorpius & Libra: the Killer has lost its pincers. The Scorpion is the brightest of the 12 zodiac consellations, and also the one which more neatly resembles the portrayed character (expecially the star signing its curved "tail"). Indeed, many night-sky lovers judge Scorpius one of the most beautiful figures in the whole Sky, almost rivalling Orion itself. Curiously, Orion and Scorpius were rivals even in Mythology. The Scorpion was envoyed by the goddess Hera to punish Orion for his vanity; it killed the Hunter with its sting, but then Zeus put them at the opposite ends of the Sky — when Scorpius sets Orion rises, so it could not threaten the man anymore. But Zeus evidently wanted to punish the animal; in the Sky the neighboring Archer is shown pointing his arrow against the Scorpion's heart marked by the bright star Antares. As if it was not enough, the poor beast even lost its pincers! Originally zodiac constellations were actually 11. Then, in Roman times, some thought 12 was a better number and used the Scorpion's pincers to create a brand new figure: Libra, the Scales. The latter is a faint and little-remarkable constellation whose quadrilateral shape could recall an ancient pair of scales. As a memory of its origins, Libra's Alpha and Beta stars are called "the southern pincer" and "the northern pincer" still today. note The northern one has a curious trait: it is an extremely-rare example of a green star. On the other hand, the Scorpion has several interesting objects. Its Alpha star, Antares, means "Mars' rival" because it's just as red as this planet (which sometimes is found near it). Like Betelgeuse, Antares is an immense super-giant star potentially-capable to swallow Mars' orbit if put where the Sun is. Its astrophysical traits are the same of Betelgeuse (see Orion), maybe Antares is only a bit smaller. Being crossed by the Milky Way, the Scorpion has several deep-sky objects: among them, the "Butterfly Cluster" (an open star cluster whose stars make together the shape of a butterfly) and Scorpius X-1, one of the several possible black holes in the external disk of our Galaxy — much smaller but more "swallowing" than the supposed one at the galactic center.
Cancer & Capricornus: the "tropical" Zodiac. If you read or remember Earth Geography books you'll find the names of the two imaginary lines called Tropics: the northern Tropic of Cancer and the southern Tropic of Capricorn. 2,000 years ago Cancer and Capricornus were respectively the highest and the lowest Zodiac constellations in the sky, about the same "latitude" of their eponymous tropics (23° north and -23° south). note Celestial latitude is technically called "Declination", but is misured in 90° degrees north and 90° south just like the Terrestrial latitude . However, because of the Precession, they've lost this privilege today. Both constellations are actually not particularly remarkable. Cancer has the shape of a "Y", and is the area devoid of bright stars between Gemini and Leo. Even though is considered the faintest figure of the Zodiac, the Crab contains a relevant open star cluster: the Beehive, also called the Praesepe or the Manger. Capricornus is also made of faint stars, has the shape of a obtuse isoscle triangle below Aquarius and the Eagle, and should portray a goat with a fish-tail.
Aries & Pisces: the Ram's First Point. We've already talked about one of the two Equinoxes, the one in Virgo. The other equinox is the "Spring point" (Fall for southerners of course) or the "Gamma point", but is more-known as the "Ram's First Point". This point has a special historical relevance: the celestial "Greenwich Meridian" (aka the line marking the "hour zero") note Celestial longitude is technically called "Right Ascension" but is measured in 24 hours, not in 360 degrees. just passes to the First Point of Aries conventionally, and this explains why the list of constellations of the Zodiac begins with the Ram. But is it really in Aries? Well, no... at least unless you're still living in ancient Greece! Today, because of the notorious Precession this point is in the near Pisces, which should be considered the start of the astrological Zodiac today. Apart from this, Aries and Pisces are quite uncospicuous constellations. Between Andromeda and the Whale, the Ram's main stars have the shape of a small triangle and portray the animal's head (the remaining body is marked by fainter stars); this triangle may get confused with the constellation called "Triangle" which is just near it and is about the same width. Pisces is a wide figure similar to a "L" visible in the northern Fall around the Great Pegasus' Square. Despite its size the Fish is one of the faintest Zodiac constellations. It represents two generic fishes united with their tails by a rope; the fish placed more south is marked by a small ellipse of stars just near the "Ram"'s first point.
Aquarius: the Heavenly Waters. One day the Ram's First Point (now in Pisces) will go in Aquarius: when so, we'll be in the Aquarius Era. But don't worry: you have to wait only 600 years. Like most Fall constellations (Spring for southerners) the Water-Carrier is faint and with an irregular shape, but is the second biggest constellation of the Zodiac. Even though is crossed by the Equator, Aquarius is almost-totally in the Southern Emisphere; you could see it under the "Great Square" of Pegasus, but good luck if you manage to see a man with an amphora. A small "Y" represents his amphora spilling water. This water is at the origin of the Heavenly Waters: that is, the sky area with Aquarius in its center, populated by many water-creatures: the Fishes, the Capricorn, the Whale, the Dolphin, and also the Southern Fish (see the next folder). Despite its weakness Aquarius contains an important object: the Helix Nebula, the nearest "planetary nebula". note Planetary nebulas are usually round in shape deceptively resembling planets, hence their name. At their center there's a White Dwarf Star. Planetary nebulas are the material ejected away from a star with a mass similar of the Sun when it explodes (it can explode more than once); like the nebulae originated from a Supernova, planetary nebulas will disperse their gas becoming invisible in the future. According to astronomers, the next 5 billion years the inflated Sun will explode forming a planetary nebula. All what will remain of our Star would be a tiny White Dwarf, which in billion years will "go out" becoming an hypothetical "Black Dwarf". For obvious reasons, we can hardly imagine what will be the exact destiny of our Earth after the death of the Sun. And is also the only constellation to be the apparent origin of three meteoric swarms each year: the Delta Aquarids, the Eta Aquarids, and the Iota Aquarids, all faint and difficult to see.
Southern Ancient Constellations
Very few constellations entirely below the celestial Equator have been known since antiquity. Greeks and Romans weren't able to see the deepest portion of the southern sky (although thanks to precession they saw a bit more of some parts, and a bit less of others): so, most southern constellations were invented in the modern era. But there are also exceptions. We've already seen five of them (Canis Major, Libra, Scorpius, Sagittarius & Capricornus); the others are listed below.
Centaurus: the Centaur. The other celestial centaur other than Sagittarius, Centaurus can be considered the southern counterpart of the Great Bear. It's the biggest entirely-southern constellation (after Eridanus, which barely touches the Equator), and is at the same time one of the brightest, just like the Bear in the northern emisphere. The Centaur has a complex shape; only the "head" and the human torso of the creature are well-visible from most of the USA during the spring. The Centaur's two main stars are among the most luminous in the firmament and portray its front feet, but since are in the southern extremity of the constellation, they are visible from the most southern USA only. Curiously, both are commonly-known with more than one name: Alpha Centauri is also called Rigil Kentaurus or Toliman; Beta Centauri is also Hadar or Agena. Beta is a blue star, while Alpha is yellow; since they appear near the Southern Cross, they aid the latter to find the South Pole. Despite its name, Omega Centauri is not a star: it is the brightest Globular Cluster in the sky, even more than the one visible in Hercules, but is visible to the naked eye as an uncospicuous starlet. Also famous is a giant elliptical galaxy outside our Local Group called "Centaurus-A", which shows a dark stripe at its equator and emits powerful radio signals. These peculiar characteristics are due to the collision of Centaurus-A with a smaller spiral galaxy. note Collisions of galaxies are not so rare as one might think: galaxies are relatively close to each other within a "cluster", and when colliding they emit powerful radiations detectable from Earth. However, since galaxies are not solid bodies they actually fuse each other when "colliding". Moreover, since a galaxy is mainly made of dust and gas, no one of its stars will probably get destroyed in the process.
Alpha Centauri deserves a special mention. It can be renamed the "star of the records": it's definitively the closest star to our Sun (just 4.4 light-years from us); it's the third most luminous star in the firmament after Sirius and Canopus (see below). And is also the most Sun-like among all the 1° magnitude stars: only a bit bigger and with about the same external temperature of "our" own Star. In short, it's basically another Sun. But wait: Alpha Centauri is actually a triple star. The Sun's "twin" is Alpha Centauri A, and is only the biggest member of its system: the second member, Alpha Centauri B, is also yellow but much smaller than the Sun. The third member is even less conspicuous: Proxima Centauri, a "red dwarf" similar to the Barnard's Star and invisible to a naked eye like the latter. Proxima means "the near one" in Latin; indeed, THIS has been the real closest star to us. note At least, since it was discovered; the three stars actually turn around each other changing periodically their position in the space. One day, the Proxima will be less-close to us than Alpha Centauri A and/or Alpha Centauri B. It was formerly believed that only solitary stars like the Sun or the Barnard's Star can develop a true planetary system, but just recently one was spotted in close orbit around Alpha Centauri B, and astronomers predict that others could exist in further orbits.
Eridanus: the Eridan River. The Eridan River rivals Hydra the Sea-Snake for the title of "the longest constellation in the sky". It's a sort of enormously-vast "inverted S" made of weak stars, whose "spring" is just below the Equator near Rigel (one of Orion's feet), while its "mouth" is not far from the South Pole. If it represents a Real Life river or a legendary one is uncertain. The only bright star of the River is just in its mouth: Achernar, the 9th brightest star in the firmament. This is a bluish star placed at the opposite end of the South Pole with regard to the Alpha-Beta Centauri couple; as the Pole is in the middle between Achernar and the latter, Achernar can help southern observers to better-find the pole itself. Even though this star is not visible from the northern USA, most of the river goes above the U.S. horizon in winter times. Eridanus contains also other two interesting stars: "Epsilon Eridani" (a close star similar to the Sun which is surrounded by a planetary system), and "40 Eridani" (a triple star whose smallest members are a red dwarf and a white dwarf). note Here is a list of the eight stars closest to us nowadays: 1) Proxima Centauri; 2) Alpha Centauri A; 3) Alpha Centauri B; 4) The Barnard's Star (in Ophiuchus); 5) Wolf 359 (in Leo); 6) Lalande 21185 (in Ursa Major); 7) Sirius A (the main Dog's Star); 8) Sirius B (the "white dwarf" companion of Sirius A). Six of them are dwarf stars ("red dwarfs" except for Sirius B), all so faint they are invisible to a naked eye. On the other hand, both Alpha Centauri A and Sirius A are slightly bigger and brighter than the Sun; their inherent luminosity and their closeness to us make them appearing the third and the first brightest stars in our sky.
"Argo Navis": the Ship Argo. Originally, the legendary ship of the Argonauts was one single constellation in the southern emisphere. Between the Centaur and the Great Dog, Argo Navis was by far the biggest constellation in the Sky; but in the 1700 century one astronomer (Lacaille) thought it was really too large and divided it in three distinct constellations: Carina the Keel, Puppis the Stern, and Vela the Sails (all described in the next folder), each of them is still larger than most other constellations below the Equator. Before the division, however, the usual Greek letters have already been assigned to the whole Ship Argo. As a consequence, the stars of each of the three portions of the ship has only some greek letters and not others. For example, both the Sails and the Stern haven't any Alpha star. Just for the record, the letters of the greek alphabet are: Alpha, Beta, Gamma, Delta, Epsilon, Zeta, Eta, Theta, Iota, Kappa, Lambda, Mu, Nu, Xi, Omicron, Pi, Rho, Sigma, Tau, Upsilon, Phi, Chi, Psi, and Omega.
Lesser southern constellations. Most of the smallest/weakest constellations below the Equator are Modern, but some are Ancient. Among them, Piscis Austrinus the Southern Fish is visible in the Fall (for U.S. people), represents a generic fish swimming in the Heavenly Waters just under Aquarius, and is actually shown drinking the water spilled by the Water-Carrier! The fish's mouth is signed by a bright bluish star, Fomalhaut (the only 1° magnitude star in this celestial area), but the rest of its body is like a small faint ellipse. Just below Orion's feet is Lepus the Hare: hares were arguably among the Hunter's favorite preys, and the one portrayed appears chased by his Great Dog. "Pressed" against the two biggest constellations of the sky (Virgo and Hydra) you could see Corvus the Raven and Crater the Cup, both just below the Equator and upon the monster's huge body. The Raven is a small quadrilater portraying the bird pecking the Hydra's body; the Cup has some resemblance with an ancient cup. The four constellations above could be well-visible from the USA; other "lesser southern constellations" are harder to spot because are closer to the south Pole. The most notable is Lupus the Wolf, an irregular group of stars just beside Centaurus — and actually forming one single figure with the latter. The wolf was originally conceived as a generic wild animal, and is shown held with a spear by the centaur as an offer to the Goddities. Nearby there is the site of the sacrifice: Ara the Altar, a small figure below the Scorpion's "tail", and one of the most southern ancient constellations. Finally, Corona Australis the Southern Crown. This is the southern counterpart of Corona Borealis, a little semicircle of faint stars just below the Archer's feet.
Modern constellations make nearly half the constellations in the Sky. The vast majority of them are in the celestial Southern Emisphere. All were created between the 1500 and the 1700 century, either to fill the still "empty" spaces in the Sky, or by taking some stars away from other pre-existing figures. By far the most famous modern constellation is the Southern Cross, used by people living below the Equator to identify the South direction of the Earth. All the others (except four) were invented by only three astronomers: Bayer, Hevel, and Lacaille.
Crux: the Southern Cross. Contrary to what you might think, the Southern Cross is not in the exact celestial South Pole: it is only near the pole, pointing the latter with the longest of its arms. Encircled by the Centaur's legs, Crux was originally a portion of Centaurus, but Spanish and Portuguese navigators deemed it a distinct figure in the 1500th century. But is actually not cross-shaped: it is actually a small rhombus-like quadrilater. Sadly, Crux is only visible from the extreme south of the USA (Florida, Hawaii, and even a bit of Texas). But for Australian and New Zealand people the Cross can appear near the Zenith; its brightness and its usefulness to find the actual South Pole has made it an icon in these nations. note It's worthy noting many other insular nations in the Pacific Ocean have one reference to the Southern Cross in their flag, not only the well-known Australian and New Zealand examples. The New Zealand flag portrays only the four stars marking the points of the cross, while the Australian one show also a fifth weaker star, plus a brighter one near the Cross which is arguably Alpha Centauri. Also note that the Australian flag's stars are white, while those of the New Zealand flag are red. Actually, the only way to tell the two flags apart from each other is watching their respective Southern Crosses. The astonishing thing is, the famous cross is actually the smallest by area among all the 88 constellations. The four stars forming the points of the cross have names that are Portmanteaus: Acrux, Becrux, Gacrux & Decrux are the shortened versions of Alpha Crucis, Beta Crucis, Gamma Crucis, and Delta Crucis. Epsilon Crucis is the fainter star shown in the Australian flag, near one side of the quadrilater. Despite its smallness, Crux contains two notable objects whose names make an ironical contrast: the Jewelry Box and the Coal Sack. The former is a beautiful "open" cluster visible with a telescope, whose stars are of different colors like gems; the latter is a great dark nebula easily visible to the naked eye because it seems making a hole in the Milky Way.
Carina: the Keel of the Ship Argo. As said in the former folder the Ship Argo doesn't exist anymore as a single constellation: in the 1700s the astronomer Lacaille divided it in three distinct constellations, each of them is today accepted as a proper constellation on its own. Carina the Keel is the southernest (even closer to the South Pole than the Southern Cross itself), and is surely the most relevant of them. Its main stars form roughly the shape of a "W" resembling a bit Cassiopeia in the North Emisphere. One end of the "w" is marked by Canopus, which is not only the Alpha star of Carina but also of the whole former "Ship Argo". It's interesting that the three most luminous stars in the Sky are all in the Southern Emisphere: indeed, Canopus is the second brightest star in the whole firmament after Sirius and before Alpha Centauri. While the latter are small and near stars, Canopus is a distant yellowish "super-giant" hundreds of light years from the Sun, one of the greatest 1° magnitude stars. note Curiously, the northern Polar Star is very similar to Canopus in size color & distance, but is less-luminous. It show also a bit of variability, and is officially classified as a "cepheid" star (see Cepheus above). Sadly, if you're American you can spot Canopus only from the south USA (in Winter times, just below Sirius), and like the Southern Cross and Alpha Centauri it's never seen far from the southern horizon. But even more striking is another star of the Keel, "Eta Carinae", which some nickname "the monster star". This is a supermassive star with a mass 100 times greater than the Sun (even Betelgeuse and Rigel are unpretentious in comparison!), varying unpredictably its brightness. Visually appears as an uncospicuous starlet, but in the XIX century Eta Carinae briefly became the second most luminous star in the whole firmament, even brighter than Canopus itself! During these events the star ejects part of its external matter in the space, to the point it has formed a huge nebula around it, named the Eta Carinae Nebula note while the innermost portion of the nebula itself (made famous by a recent photo of the Hubble Telescope) has received the curious name "Homunculus nebula", lit. the "little-man" nebula.. Some experts think this star might become a Supernova in the next 10,000 years.
Puppis & Vela: the Stern and the Sails of the Ship Argo. These parts of the former Ship Argo are less luminous than the Keel a but more northern, thus easier to spot from the USA. The Stern is a long irregular constellation visible in winter between Sirius and Canopus; the Sails is another irregular figure similar to a polygon, but is better-visible in Spring. If we could see the whole "ship", Vela would appear just above Carina. Two stars of the Sails and two of the Keel form together the so-called "False Cross", a small quadrilater deceptively similar to the true Southern Cross. However, being the false cross larger weaker & farther from Alpha/Beta Centauri than the true cross, it's easily unmasked. As said above, both the Stern and the Sails lack the Alpha star. The Stern's main star (the Zeta) is one of the bluest and hottest known stars; the Sails' main star (the Gamma) is even more peculiar, as it has lost its external shell. Both constellations are crossed by the Milky Way; the Stern includes several Open Clusters, while the Sails contains a huge but faint nebula with a rest of a Super-Nova inside. Beside Puppis you could see another smaller and fainter modern constellation: Columba the Dove. Created at the end of the 1500 century, this is maybe the only constellation in the sky to portray a Christian figure, the Great Deluge-related Noah's Dove. If so, the Ship Argo could be alternatively considered the Noah's Ark.
Camelopardalis & Monoceros: the Giraffe and the Unicorn. These two constellations (plus Columba above and Coma Berenices below) were created by some astronomers who weren't neither Bayer nor Hevel nor Lacaille. All them were invented in the 1500 century — about the same years of the Bayer's constellations but before the Hevel's and Lacaille's ones. Both Camelopardalis and Monoceros were ideated by the same person, and portray two similar figure: a giraffe (once called "camelopard") and an unicorn (the legendary one-horned horse). note In the 1500 century the African big fauna was not as familiar to european people as is today; a critter like the giraffe could easily be passed off as something mythical, like an unicorn. Camelopardalis the Giraffe is one of the six constellations closest to the North Pole, together with the Dragon, the two Bears, the King, and the Queen; but is by far the faintest of them, to the point it is hardly visible even when we're far from city lights. The Giraffe is nonetheless the largest modern constellation, well-filling the apparently "empty" area between the two Bears, Perseus, and Auriga. On the other hand, Monoceros the Unicorn is equatorial; it's the space apparently devoid of stars between Orion and his two Dogs. In spite of being easily overshadowed by the Hunter, the Unicorn is crossed by the Milky Way and contains two interesting nebulae, the Rosette Nebula similar to a flower, and the dark Cone Nebula.
The 7 Hevelius' Constellations. Polish astronomer John Hevel (Hevelius in latin) note In the 1600 Europe there was still the habit of "latinizing" the names of important people. invented at the end of the 1600 century seven new constellations in the Northern and Equatorial sky. Before this, another astronomer had already invented another figure, Coma Berenices (which is here for convenience). This oddly-named constellation (literally "Berenices' Hair") is one of the weakest constellations of the Northern Sky, and portrays the cut hair of an ancient Egyptian queen. Between the Herdsman, the Lion & Virgin, the Coma is nonetheless interesting because some galaxies of the Virgin Cluster are actually visible in this constellation. Coma Berenices also contains the North Pole of our Galaxy. note that is, the perpendicular point with regard to the Milky Way's plan. In this area distant galaxies are easier to see than near the Milky Way, being not "darkened" by the dusts of the latter. The seven Hevel's constellations are very faint as well, but usually portray Real Life animals. One of the most notable is Canes Venatici the Hounds. Between the Great Bear, the Herdsman & and the Berenice's Hair, it is apparently made by only two stars, Alpha & Beta, note Curiously, many Hevel's constellations have only one or two stars labeled with a greek letter., each portraying one of the Herdsman's two hunting dogs. However, the Alpha is also dedicated to the english king Karol 1th. The Hounds contain also one of the most famous galaxies outside the Local Group: the Whirlpool Galaxy, the first ever galaxy whose spiral shape has been revealed with the telescopes (1800 century). Hevelius also invented Lynx the Lynx to fill the "empty" space between the Great Bear, the Twins and the Coachman; it's said he called it with this name because "only lynx-eyed people can glimpse it"! This is the largest Hevel's constellation but has only one star with a greek letter (the Alpha). Even though mainly visible in Winter, Lynx is placed very north in the Sky, and could at high latitudes be visible all year round. Near the lynx there is another celestial cat invented by Hevel, but even less conspicuous: Leo Minor the Little Lion portays a lion cub between the Great Bear's paws and the more familiar Lion's head. The Little Lion's only star with a Greek letter is, oddly, the Beta. Between the Swan and the Eagle, other than the Arrow you could also "see" Vulpecula the Little Fox (or more simply the Fox); note Once called "Vulpecula com Anser", the Little Fox with Goose; old portrayals show the fox holding a dead goose with its mouth. actually its stars are so faint, the constellation is almost invisible to a naked eye. Nonetheless, the Fox interests night-sky observers because contains two notable objects: the Dumbbell Nebula (perhaps the easiest planetary nebula to see from Earth), and the Coathanger — a small group of starlets visible with binoculars, that really resembles the eponymous thing. Between the Swan and the Winged Horse there is Lacerta the Lizard, a bunch of stars which are very north in the sky like those of the Lynx. However, this figure was originally conceived as the "Scepter and Hand of Justice" before becoming the Lizard. Just below the Equator is Scutum the Shieldnote More precisely the Sobieski's Shield: John Sobieski was the Polish king at Hevel's times., another tiny uncospicuous constellation crossed by the Milky Way, near the Eagle and the Snake's Tail. Finally, Sextans the Sextant, an almost-invisible Equatorial constellation between the Lion and Hydra: a poor homage to the sextant, one of the most important astronomical instruments in the past.
The 12 Bayer's Constellations. Johann Bayer was the German astronomer who invented in the 1600 century the usage to list the stars in a constellation with Greek letters. He also added 12 new constellations in his Atlas to fill the still-empty-at-the-time deep southern Sky (even though they were already invented by other colleagues in the 1500 century). Most Bayer's figures are small and faint, and many are too close to the South Pole to be spotted from the USA; nonetheless, they are generally brighter and more recognizable than those invented by Lacaille (see below). Unlike the latter, Bayer's constellations usually represent exotic Real Life animals (which were at the time compared to the mythical beasts portrayed in the classical constellations). Five are birds: Grus the Crane, note This is the brightest and most northern Bayer's constellation, just below the luminous star Fomalhaut (in the Southern Fish). The Crane's shape resembles a bit a miniature Swan.Phoenix the Bird-of-Fire, note The only Bayer's constellation to portray a mythical critter — the famous bird which periodically reborns from its own ashes. Phoenix is an irregular but relatively bright figure between Grus and the luminous star Achernar (signing the mouth of the Eridan River).Pavo the Peacock, note Closer to the South Pole than Grus and Phoenix, it's a relatively large constellation made of an ellipse of faint stars, plus another star brighter than the others which the Royal Air Force (which required proper names for stars used in aerial navigation) also named Peacock.Tucana the Toucan, note A faint figure not far from the celestial South Pole. Being close to each other, Grus, Phoenix, Pavo & Tucana are sometimes nicknamed "the four birds". and Apus the Bird-of-Paradise. note One of the smallest and weakest Bayer's constellations, extremely close to the South Pole. Curiously, Apus means "feet-less" but the Real Life Bird-of-Paradise actually does have the feet! Two are reptiles: Hydrus the Male Sea-Snake, note A smallish triangle between Achernar and the South Pole, it should better named the Southern sea-snake. Hydrus is not the husband of Hydra, the "female" sea-snake: the former actually indicates a real creature (a small tropical water snake), while Hydra represents a huge legendary monster. and Chamaeleon the Chameleon. note Just a stone's throw from the South Pole, the chamaeleon is an uncospicuous figure, but is nonetheless used sometimes to aid the finding of the Pole itself. Two are fish: Dorado the Golden Fish, note A small elongated figure between Canopus and Achernar, Dorado does not portray the household goldfish but a large marine fish, the Coryphenid or "dolphinfish". However, some identify Dorado with a Swordfish. and Volans the Flying Fish. note Another small faint figure near the other Bayer's fish. In the sky Volans is shown "flying" against the Ship Argo to escape Dorado; in Real Life the coryphenid actually chases flying-fishes when they're gliding out of water. Finally, one is an insect: Musca the Fly. note Although very small this constellation is relatively easy to find because is adjacent to the Southern Cross (a small part of the former's "Coal Sack" trespasses in Musca). However, the Fly was originally portrayed as a Bee. The remaining two are Indus the Indiannote The only modern constellation showing a human figure, precisely a Native North American. Between the Crane, the Peacock & the Toucan, the Indian is quite indistinct but contains a near star very similar to the Sun. and Triangulum Australe the Southern Triangle. note The constellation with the longest Latin name. Between Alpha Centauri and the Peacock, this is the southern counterpart of Triangulum. Both triangles are very small figures, but the Southern one is brighter and more regular.. Dorado and Tucana are the most interesting among all them. Each contains one of the two small galaxies "satellites" of our own Galaxy: the so-called "Magellanic Clouds". note Portuguese navigator Magellan saw them when travelling below the Equator, and was the first to report them to the western world. The Large Magellanic Cloud or LMC is mainly in Dorado; the Small Magellanic Cloud or SMC is completely included in the Toucan. Hydrus (the "male sea-snake") appears between them. Unusual for galaxies, the Magellanic Clouds are perfectly visible to a naked eye, appearing like faint "clouds" near the Milky Way. They actually are two "dwarf galaxies" very close to our Milky Way Galaxy, and are about 180,000 light-years from us — much closer than every other galaxy of the Local Group. Both are classified as "irregular" galaxies because they lack a precise shape, and are mainly made of young stars, gas & dust like the external disk of our own Galaxy. The LMC contains also a huge nebula called Tarantula Nebula for its (allegedly for some) spider-like shape. One star near this nebula exploded in year 1987 as a Supernova: it has been the only supernova seen with naked eyes since the telescope was invented by Galileo in the 1600 century. In the Tucana there is also "47 Tucanae", the second brightest Globular Cluster in the Sky after Omega Centauri. Even though seems close to the SMC, 47 Tucanae actually belongs to our own Galaxy, as well as another smaller globular cluster visible in Pavo, the Peacock.
The 14 Lacaille's Constellations. Lacaille was a French abbey who invented in the 1700 century 14 new constellations in the Southern Emisphere. note Lacaille was also the creator of Carina, Puppis & Vela aka the three parts of the former Ship Argo. Since they are simple divisions of a classical constellation most astronomers do not classify them as proper Lacaille's constellations. Lacaille's constellations include some of the faintest and least-known figures in the whole Sky, even though two enjoy more fame: Sculptor the Sculptornote It doesn't portray the man but only his study however. and Fornax the Ovennote More precisely the Chemical Oven, used for scientific experiments. (and for a different reason also a third, Octans, see at the bottom). As a group, Lacaille's figures appear mixed with the Bayer's ones in the deep-south sky, even though some are more northern and placed between ancient constellations. Lacaille created them mainly to celebrate Man's creativity: unusually for constellations, they don't represent human or animal character but scientific / artistic objects. Some astronomers don't belove them much, judging their creation not strictly necessary and considering their names cold and unexpressive — disrupting the "legendary" atmosphere created by the other constellations. They are: Antlia the Pneumatic Machine, note Between Hydra and the Sails of the Ship Argo, it's an almost-invisible figure portraying a scientific instrument to create the artificial void, though it can also be visualized as a simple air-pumpCaelum the Burin, note Between the Dove and the right bank of the Eridan River, it represents the Sculptor's Chisel. It's the constellation with the least number of stars visible to the naked eye: only 4. Circinus the Compasses, note Pressed between Alpha Centauri and the Southern Triangle, it's the Lacaille's constellation with the smallest area, and resembles the eponymous tool to draw circles. Horologium the Clock, note More precisely a Pendulum Clock, is an almost-empty area near Achernar and the Male Sea-Snake, and is also close to the Burin above.Mensa the Table, note Not an actual table but the Table-Mountain near Cape Town (South Africa), from where Lacaille made its observations of the Southern Sky Emisphere. One of the constellations closest to the South Pole, Mensa has been quoted "the faintest constellation in the whole sky", but contains a small portion of the Large Magellanic Cloud (see "Dorado" above).Microscopium the Microscope, note Just as faint as the Table but much more northern than the latter. Between Sagittarius, Capricornus & Piscis Austrinus, some have quoted the Microscope "the most unnecessary constellation in the sky".Norma the Square, note Between the Wolf and the Altar, this tiny figure portrays a Set Square (though some call it the Ruler), and has not any Alpha star. Pictor the Painter, note Like Sculptor it's not the human; its complete name is the Painter's Easel. Between the bright star Canopus and the Large Magellanic Cloud, one Pictor's stars was the first star to have revealed a possible planetary system. Pyxis the Compass, note The most northern Lacaille's constellation, Pyxis was originally the mast of Ship Argo; now it represents the tool to find the magnetic North, and shouldn't be confused with the Compasses. Some mention Pyxis as "the forth portion of the former Argo Navis", but unlike Carina Puppis & Vela it has its own greek letters including an Alpha star.Reticulum the Net, note A small but relatively visible rhombus, representing a small "net" Lacaille used to put on the ocular of his telescope. Pictor, Dorado, Reticulum & Horologium make together a foursome of modern constellations between Canopus and Achernar. and Telescopium the Telescope, note Below Sagittarius and the Southern Crown, it's a modest but right homage to the most important astronomical tool. Significantly, the Telescope was put by Lacaille near the Microscope. other than the aforementioned Sculptor, Fornax, and Octans. The Sculptor and the Oven are placed near each other below the Whale; the Sculptor is near the bright star Fomalhaut, the Oven is encircled by a bend of the Eridan River. They are medium-sized constellations whose area is visible from the USA. Though very difficult to spot because of their faintness, both are interesting because contain several galaxies. Some are small members of our Local Group, other pertain to distant clusters. One galaxy (in Fornax) is an often-cited example of a "barred-spiral galaxy": it has only two spiral arms protruding from a central "bar". note Interestingly, it was recently hypothized that even our Galaxy is a barred spiral Galaxy, but the central bar is not visible from Earth. The Sculptor contains the South Pole of our own Galaxy; this explain why so many distant galaxies are visible in these two constellations (see also "Coma Berenices" above). Let's end our long trip among constellations with Octans the Octant. note This was an ancient astronomical instrument very similar to the Sextant; both instruments are portrayed in their own constellations. This faint triangle-shaped constellation has a very special privilege: is this the costellations whose area contains the celestial South Pole. Sadly, the Octant's visible star closest to the south Pole is barely visible to a naked eye.
Constellations ordered by alphabet
NOTE: If the constellation has some remarkable trait, this is signaled.
ANDROMEDA: includes the Great Andromeda Galaxy
AQUARIUS: zodiacal, includes the Helix Nebula
AQUILA: includes the bright star Altair
ARIES: zodiacal, formerly included the "first point of Aries"
AURIGA: includes the bright star Capella
BOOTES: includes the bright star Arcturus
CAMELOPARDALIS: is near the North Pole
CANCER: zodiacal, gives the name to the Northern Tropic
CANES VENATICI: includes the Whirlpool Galaxy
CANIS MAJOR: includes the extremely bright star Sirius
CANIS MINOR: includes the bright star Procyon
CAPRICORNUS: zodiacal, gives the name to the Southern Tropic
CARINA: is one of the three parts of the Ship Argo, includes the bright star Canopus and the Eta Carinae Nebula
CASSIOPEIA: is near the North Pole
the bright star more similar to the Sun (Alpha Centauri)
another bright star (Beta Centauri)
the closest star to the Sun (Proxima Centauri)
the brightest globular cluster (Omega Centauri)
CEPHEUS: is near the North Pole
CETUS: includes the variable star Mira
CRUX: is the smallest constellation, includes the "Coal-Sack" nebula
CYGNUS: includes the bright star Deneb and the North-America Nebula
DORADO: includes the Great Magellanic Cloud
DRACO: is near the North Pole
ERIDANUS: the biggest constellation below the Equator, includes the bright star Achernar
GEMINI: zodiacal, includes the bright stars Castor & Pollux
HERCULES: includes the bright globular cluster M13
HYDRA: is the biggest constellation
LEO: zodiacal, includes the bright star Regulus
LIBRA: is the last-created zodiacal constellation
LYRA: includes the bright star Vega and the Ring Nebula
MONOCEROS: includes the Rosette Nebula
OCTANS: includes the celestial South Pole
OPHIUCHUS: is the 13th zodiac constellation, includes the Barnard's Star
ORION: is usually considered the most beautiful constellation in the sky, and includes:
the bright super-giant stars Betelgeuse and Rigel
the "Orion's Belt"
the bright Great Orion's Nebula
the dark Horsehead Nebula
PEGASUS: includes the "Great Pegasus Square"
PERSEUS: includes the variable star Algol
PISCES: zodiacal, includes the modern "first point of Aries"
PISCIS AUSTRINUS: includes the bright star Fomalhaut
PUPPIS: is one of the three parts of the Ship Argo
SAGITTARIUS: zodiacal, includes:
the highest number of objects in the Messier Catalogue
the Lagoon Nebula and Triphid Nebula
the center of our own Galaxy
SCORPIUS: zodiacal, includes the bright star Antares
SERPENS: is the only constellation split in two, includes the Eagle Nebula
TAURUS: zodiacal, includes:
the bright star Aldebaran
the two main "open clusters" of the Sky, the Pleiades and the Hyades
the Crab Nebula
TRIANGULUM: includes the Triangulum Galaxy
TUCANA: includes the Small Magellanic Cloud
URSA MAJOR: the biggest constellation above the Equator, includes:
the "Great Dipper" (the most famous stellar figure of the sky)
the multiple star Mizar
URSA MINOR: includes the celestial North Pole
VELA: includes one of the three parts of the Ship Argo
VIRGO: the biggest constellation of the Zodiac, includes:
the bright star Spica
the Virgo Cluster of galaxies and the Sombrero Galaxy
VULPECULA: includes the Dumbbell Nebula
Constellations ordered by celestial latitude
IN THE NORTHERN EMISPHERE note Here we put only the constellations totally or almost-totally above the Equator
From about +50° up to the North Pole: Ursa Minor (which contains the +90° point), Draco, Camelopardalis, Cepheus, Cassiopeia, and the northern part of Ursa Major (where the "great dipper" is)
From about +30° up to about +50°: The southern part of Ursa Major, Lynx, Auriga, Perseus, Andromeda, Lacerta, Cygnus, Lyra, the northern parts of both Hercules and Bootes, and Canes Venatici
Around +30°: Leo Minor, Triangulum, Vulpecula, Corona Borealis
From the Equator up to about +30° Leo, Cancer, Gemini, Taurus, Aries, Pisces, Pegasus, Equuleus, Delphinus, Sagitta, the southern parts of both Hercules and Bootes, Coma Berenices, and Canis Minor (the latest one has its southern boundary just on the Equator)note Small portions of Leo, Taurus & Pisces are in the Southern Emisphere.
NOTE: All these constellations are above the Ecliptic, except for the Zodiacal ones (which, by definition, are crossed by the Ecliptic) and Canis Minor which is below it.
IN THE EQUATORIAL BELT note Here we put only the equatorial constellations evenly split between Northern and Southern Emisphere
Above the Ecliptic: Aquila, Serpens
Crossed by the Ecliptic: Ophiuchus, Virgo
Below the Ecliptic: Monoceros, Orion, Cetus
Complete list of the constellations crossed by the Equator (ordered by celestial longitude from 0h to 24h): Pisces, Cetus, Taurus, Eridanus, Orion, Monoceros, Canis Minor, Hydra, Sextans, Leo, Virgo, Serpens Caput, Ophiuchus, Serpens Cauda, Aquila, Aquarius, and again Pisces.
Complete list of the constellations crossed by the Ecliptic (ordered again from 0h to 24h): Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus, Sagittarius, Capricornus, Aquarius, and again Pisces.
IN THE SOUTHERN EMISPHERE note Here we put only the constellations totally or almost-totally below the Equator
From the Equator down to about -30°: Libra, Scorpius, Sagittarius, Scutum, Capricornus, Aquarius, the northern part of Eridanus, Lepus, Canis Major, Hydra, Sextans, Crater, Corvus and the northern part of Puppisnote Small portions of Aquarius, Hydra & Sextans are in the Northern Emisphere, while Eridanus touches the equator with its northern boundary. On the other hand, Scorpius & Sagittarius go below to reach -45°,
NOTE: All the non-zodiac constellations above are below the Ecliptic except for Scutum which is above it.
Around -30°: Piscis Austrinus, Sculptor, Fornax, Pyxis, Antlia
From about -30° down to about -50°: The northern part of Centaurus, Lupus, Corona Australis, the central part of Eridanus, Columba, Caelum, the southern part of Puppis, Vela, Grus, Phoenix, and Microscopium
From about -50° down to about -70°: The southern part of Centaurus, Crux, Carina, Pictor, Dorado, Reticulum, Horologium, the southern part of Eridanus, Hydrus, Tucana, Indus, Pavo, Telescopium, Ara, Norma, Triangulum Australe, Circinus, Musca, Volans
From about -70° down to the South Pole: Mensa, Apus, Chamaeleon, and Octans (the latest one contains the -90° point)