Constellations groups of stars provide astronomers with the road map of the galaxy. Identify the appositive or appositive phrase

groups of stars

An appositive phrase follows a noun and defines it using a noun. The word constellations is a noun. It is defined as groups of stars. Usually, an appositive phrase is set off by commas. Another example of an appositive phrase is: My dog, a yellow lab, likes to play ball. The appositive phrase is "a yellow lab". The phrase describes the noun - dog.