"Star" can be both a count noun and a mass noun, depending on the context.

Here's how:

Count Noun:

* When referring to individual stars in the sky: "There are billions of stars in the Milky Way galaxy."

* When referring to famous people: "He's a movie star."

Mass Noun:

* When referring to the substance of a star: "The star is made of hydrogen and helium."

Let me know if you'd like more examples!