Around 1984, when I was 4 or 5, I was walking past a music store and I saw a record that had on the cover what looked like a spectrum, as I remember it a long, trapezoid or jagged trapezoid shape, travelling through outer space. That at least is how I remember it. Two possible candidates have come forward for it. One is the well-known cover for Dark Side of the Moon:

http://www.sorouche.com/journal/uploads/entries/DarkSideoftheMoon.jpg

However, I doubt this is the one. Of course it is possible that my memory got skewed quickly after I saw it, but I think there was no prism, that the spectrum was more defined, and that it most definitely had stars all around.

This one looks more like it, Rainbow's "Down to Earth":

http://hardrockheavymetal.files.wordpress.com/2006/07/img17b45378g3d3s6.jpg

I don't remember the bow going around the Earth, and remember the spectrum as going in the direction away from, not toward the viewer, but it's of course easy to badly remember such things, good I remember the details I do.

For now, the second cover seems the most likely candidate. Any other suggestions which LP cover I might have seen?

hmm I was going to guess Dark Side of the Moon just based on your title ... I can tell you if you're going to listen to it get Dark Side!! Love that album. and then go ahead and cue it up and watch it with the wizard of oz ... everyone will tell you to do it ... its "the cool thing to do". & yes ... it works.