A collection of stars and gas in space is referred to as a galaxy. Galaxies vary widely in size and structure, containing billions to trillions of stars, along with gas, dust, and dark matter. The Milky Way, which is the galaxy that includes our solar system, is a spiral galaxy, while others, like the Andromeda galaxy, exhibit different shapes such as elliptical or irregular. Galaxies are fundamental components of the universe and are part of larger structures known as galaxy clusters. Studying galaxies helps astronomers understand the formation and evolution of the universe over billions of years.