Yes, the word astronaut is a common noun, a word for any astronaut anywhere.
A proper noun is a word for a specific person, place, thing, or a title; for example:
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No, the noun Jupiter is a proper noun, the name of a specific planet. The common noun for Jupiter is planet.
'Noun' is the collective word for common nouns and proper nouns. The word 'star' is a common noun, because individual stars have names, which makes the noun a proper noun. e.g. the star , Sirius , is a proper noun, because Sirius is the name of a given star.
The common noun would be "dwarf planet."
The noun 'eyes' is a plural, common, concrete noun; eyes are things. . The word eyes is also a verb.
The word eyes is a common, plural, concrete noun.