Parts of sky maps (7)
I believe the answer is:
nebulae
'parts of sky maps' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nebulae that I've seen before include "where stars are born" , "Stardust" , "Gas or dust clouds in space" , "Interstellar gas clouds" , "Bright patches in sky from distant galaxies" .)