Hesperus vs Vesper

Hesperus and Vesper both are nouns.

Word	Noun	Adjective	Verb	Adverb
Hesperus	Yes	No	No	No
Vesper	Yes	No	No	No

As nouns, Hesperus and Vesper are synonyms defined as:

Hesperus and Vesper: a planet (usually Venus) seen at sunset in the western sky

Other synonyms of Hesperus include evening star.

Hesperus (noun)	Vesper (noun)
a planet (usually Venus) seen at sunset in the western sky	a planet (usually Venus) seen at sunset in the western sky