"Cygnus X-1" is the Explorer's Dying Dream
"Cygnus X-1" is a Stable Time Loop in a world in which All Mythology Is True
Aimee Mann's presence on the track (and, to a lesser extent, the mere existence of the song in the first place) serves solely to prove just how much Geddy doesn't sound like a female, by comparing his voice to that of an actual woman.