What is a star cluster?

Answer 1

Star clusters (or star clouds) are groups of stars.

There are two types of star clusters

Globular clusters: are tight groups of hundreds of thousands of very old stars, which are gravitationally bound.

Open clusters: are more loosely clustered group of stars, generally contain less than a few hundred members, and are often very young.

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Answer 2

In my old science book, the definition of galaxy meant a cluster of stars, so I guess that's that for you

Answer 3

They are groups that are relatively close to one another.