Through a telescope, galaxies appear as delicate whorls of soft light, some barely visible, others distinct and surprisingly symmetrical.
Galaxies are immense, remote systems of gas, dust, and billions of stars held together by gravity. They come in a wide variety of shapes and sizes—from pin-wheels, spheres, and footballs to shapeless clouds.
Astronomers once referred to some galaxies as "spiral nebulae" because they were spiral shaped and could not be resolved into stars. By the mid-1920s, however, powerful telescopes had revealed that the brightest of these fuzzy objects contained stars of their own. In 1926, the American astronomer Edwin Hubble sorted galaxies into three broad categories: spirals, barred spirals, and ellipticals. With a few modifications, his system is still used today.