The planets. The moon. The sun. All these things are part of a galaxy known as the Milky Way. Even though we live in a galaxy, however, many of us don’t know exactly what galaxies are. In fact, astronomers still don’t completely understand galaxies, and didn’t know there were other galaxies in the universe until 1924!
Q: What is a galaxy?
A: A galaxy is a huge region of space. In it are stars, planets, dust, gas, nebulae (clouds of gas and dust), and empty space. Many astronomers believe galaxies also have a black hole at the center.
Q: How many galaxies are there?
A: Astronomers think there are more than 100 billion galaxies in the visible universe.
Q: Are all galaxies the same?
A: No, in fact there are three kinds of galaxies--spiral, elliptical, and irregular. Spiral galaxies look like a pinwheel, are flat, and are centered around a group of stars. Spiral galaxies make up about 75 percent of the brightest galaxies. The Milky Way, our galaxy, is a spiral galaxy. Elliptical galaxies can be circle or oval-shaped, and can be round or flat. They are brightest at the center, and dimmer at the outer edges. Elliptical galaxies make up about 20 percent of the brightest galaxies. Irregular shaped galaxies can come in many shapes. Their unusual shape may be caused by galaxies colliding to form a new galaxy, or by stars forming within the galaxy.
Q: How many galaxies can we see from Earth?
A: Only three galaxies outside the Milky Way can be seen without a telescope. People in Earth’s Northern Hemisphere can see the Andromeda Galaxy, which is about 2 million light-years away. People in Earth’s Southern Hemisphere can see two galaxies: the Large Magellanic Cloud, which is about 160,000 light-years away, and the Small Magellanic Cloud, which is about 180,000 light-years away. However, astronomers have photographed millions more galaxies by using telescopes.
