sky vs atmosphere

sky and atmosphere both are nouns.

Word	Noun	Adjective	Verb	Adverb
sky	Yes	No	Yes	No
atmosphere	Yes	No	No	No

As nouns, atmosphere is a hypernym of sky; that is, atmosphere is a word with a broader meaning than sky:

sky (noun)	atmosphere (noun)
the atmosphere and outer space as viewed from the earth	a distinctive but intangible quality surrounding a person or thing
	the mass of air surrounding the Earth
	the envelope of gases surrounding any celestial body
	a unit of pressure: the pressure that will support a column of mercury 760 mm high at sea level and 0 degrees centigrade
	the weather or climate at some place
	a particular environment or surrounding influence

sky (verb)	atmosphere (verb)
throw or toss with a light motion