It is a common noun when it refers to the star in the centre of any solar system. It's also a countable noun (which means it can be pluralized: "suns").

6 авг. 2015 г. · It is both a common noun and a proper noun. When it is used to refer to "our" Sun (the one at the centre of our solar system) it is a proper noun. Are “sun”, “moon”, and “earth” common or proper nouns? - Quora Why is the Sun called a common noun? Why not proper noun? Sun rise a common noun or a proper noun? - Quora Другие результаты с сайта www.quora.com

25 июл. 2010 г. · If you are talking a sun in general, lowercase. If you are talking about the Sun as in our sun specifically, then capital.

8 мая 2022 г. · It can be used as both a proper noun and a common noun. The star at the center of our solar system is "the Sun." Other galaxies may have stars ...

(Here, "suns" is a common noun, but "The Sun" (the name of our sun) is a proper noun. That's why it has a capital letter.)

Sun can be a proper noun, a noun or a verb. sun used as a proper noun: The star which the Earth revolves around and receives light and warmth from.

2 июл. 2021 г. · Proper nouns are distinguished with a capital initial letter. For example: Sun / sun. Moon / moon. God / god. Superman / super man.

17 авг. 2021 г. · In English, "sun" and "moon" are treated as common nouns. A sun and a moon are kinds of things, but the sky only happens to have one of each.

7 апр. 2021 г. · Answer: Sun is a common noun - literally, because there are so many of them. Our sun, Sol, is a proper noun because we gave it a name.