Astronomy Practice Exam 2026 – Complete Preparation Guide

A nebula is best described as a cloud of dust and gases. This definition is fundamental in astronomy, as nebulas are often the regions where new stars are born, known as stellar nurseries, or they may consist of remnants from the death of stars, such as supernova remnants. In essence, nebulas serve as the building blocks of the universe, providing the materials needed for star formation and the development of planetary systems.

The other options describe different astronomical entities. A collection of stars refers to star clusters or galaxies, which are more organized structures. A cloud of stellar remnants could refer to specific types of nebulas, like supernova remnants, but it doesn't encompass the broader definition of a nebula since nebulas can also form from gases and dust prior to star formation. Lastly, referring to a nebula as a type of galaxy is inaccurate, as galaxies are vast systems that contain millions to billions of stars, along with their own nebulae, rather than being synonymous with them. Hence, the most accurate description remains that a nebula is a cloud of dust and gases.