Stars

Stars are the basic building blocks of galaxies. They are formed from the collapse of large clouds of gas and dust. The gravity of the cloud causes it to contract, and the pressure and temperature in the center of the cloud increase. The center eventually becomes so hot that nuclear fusion begins, and a star is born. Stars vary in size, mass, and luminosity. The Sun is a medium-sized star, and it is the only star that is visible to the naked eye during the day. The largest stars are called supergiants, and they can be hundreds of times larger than the Sun. The smallest stars are called dwarfs, and they are only a few times larger than the Earth. Stars have a life cycle. They begin as hot, glowing balls of gas. As they age, they cool and become less luminous. Eventually, they die. Some stars explode in a supernova, while others simply fade away. Stars are important for life on Earth. They provide the light and heat that we need to survive. They also emit radiation that helps to create the molecules that make up living things.