Out of curiosity, I decided to check the Power Windows website to see if there were any articles or notes regarding the creation of the Cygnus Books, and here's bits that I found:
. . .
So, there ya go. Neil had the idea to put "To be continued" after the purposely-subtitled "Book I - The Voyage", knowing he'd get to a sequel SOME DAY, but it looked like he wasn't going to do it on their next album, but it all happened anyway. The Cygnus Books were DEFINITELY NOT CONCEIVED AS ONE PIECE FROM THE GET-GO. From the man himself...
That all sounds about right. "The Voyage" was labeled "Book I" (and I forgot about the "to be continued" on the lyrics sheet, which I probably haven't looked at in 30 years), so it's not unreasonable to think they planned from the outset to do a "Book II," but there's no evidence that the entirety of the story was conceived prior to the recording of
Hemispheres.
For the record, I never claimed that the band *wrote* it as one single piece of music. I said that they fit together as a single piece of music. So much so that I made a mixtape with the two blended together all the way back in 1983. It was my favorite tape.
Aside from what's in the current thread, in this thread --
https://www.dreamtheaterforums.org/boards/index.php?topic=51973.35 -- you wrote "that Cygnus X-1 and Hemisphere is a single piece of music." I suppose "piece of music" is a broader term than "song," but one factor in considering whether the two Books are a single song or "single piece of music" is what the artist's intent was. And, given how short
Hemispheres is, putting the two Books back to back on a cassette was pretty common.