atlas vs star atlas

atlas and star atlas both are nouns.

Word	Noun	Adjective	Verb	Adverb
atlas	Yes	No	No	No
star atlas	Yes	No	No	No

As nouns, star atlas is a hyponym of atlas; that is, star atlas is a word with a more specific, narrower meaning than atlas:

atlas: a collection of maps in book form
star atlas: (astronomy) a series of star maps for different times, for example, for each month; the maps are generally drawn to a small scale and in book form.

Other hyponyms of atlas include dialect atlas, linguistic atlas.

atlas (noun)	star atlas (noun)
a figure of a man used as a supporting column	(astronomy) a series of star maps for different times, for example, for each month; the maps are generally drawn to a small scale and in book form.
the 1st cervical vertebra
a collection of maps in book form