astronomy vs major planet

astronomy and major planet both are nouns.

Word	Noun	Adjective	Verb	Adverb
astronomy	Yes	No	No	No
major planet	Yes	No	No	No

astronomy (noun)	major planet (noun)
the branch of physics that studies celestial bodies and the universe as a whole	(astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction