Galaxies are made up of stars, their orbiting planets, and the surrounding gas and dust. Gallaxies have billions of stars. They are held together by gravity and move as one unit across the universe. They can be all shapes and sizes like spirals or ellipses. Our galaxy is called the Milky Way.
Looking at galaxies out in the universe we can see all their different shapes and sizes. Some galaxies seem smaller but are really just further away. Pictures taken by the Hubble Telescope show galaxies stretching billions of light-years away in space. Because it takes that long for light to reach us, when we look at these distant galaxies, we are seeing them how they looked billions of years ago.
We live in the Milky Way Galaxy, which is just one of millions of galaxies in the Universe. If we could see the Milky Way from space, we would see a spiral galaxy, shaped like a pin-wheel. From Earth, though, the Milky Way looks like a glowing band of light across the sky that is sprinkled with stars.
The Milky Way is a disk galaxy, which means that it’s stars and gas are in a rotating disk, which appears flattened from the side with a bulging center. The building center is called the Galactic Nucleus. This flat plane was first photographed by the Nasa COBE satellite in 1990. (COBE stands for Cosmic Background Explorer).
The Milky Way is thought to have as many as 400 billion stars. Some form “star clusters” where a number of stars were formed together and are bound together by gravity. There are thousands of “open clusters” in the Milky Way, like Pleiades, with a small number of stars. There are much fewer “globular clusters” with hundreds of thousands of stars. So far we only know about 150 globular clusters in the Milky Way galaxy. The Great Globular Cluster has 200,000 stars in it.
The Milky Way also contains nebulae, with are huge, thick clouds of dust and gas where stars are born. They look like fuzzy patches of light in the night sky.
Each of the Milky Way’s spiral arms are thought to be about 4,000 light years wide. The gaps between each arm are about 2,000 light years wide. Our solar system is located on the inner edge of one of the spiraling arms of the Milky Way called the Orion Spur.
Scientists believe that there could be billions of planets orbiting stars in the Milky Way Galaxy. Some may have conditions that could support life, if they are not too hot and not too cold and have water and a protective atmosphere. Scientists call these “Goldilocks Planets.” Are there living things on some of these far away plants? Maybe someday, we will find out.
Hang a Milk Way Galaxy Poster in your classroom.
Barred spiral galaxies are different from regular spiral galaxies in that the arms of the galaxy do not spiral all the way into the center, but are connected to the two ends of a straight bar of stars. An example of a barred spiral galaxy is NGC 1300. Seen by the Hubble telescope, it is a glowing gas against its dark clouds of interstellar dust.
The Sombrero Galaxy looks flat with a fat center (like a Mexican hat, called a sombrero) to us here on Earth because it is actually tilted nearly edge-on. We are seeing it from the side. This galaxy is 50,000 light-years across and is 28 million light-years from Earth.
This is a pinwheel-shaped galaxy photographed by NASA's Hubble Space Telescope. In September 2002, the light of a supernova in this galaxy reached Earth making it possible for our astronomers to see it. This supernova was a white dwarf star that exploded and was the brightest object in the galaxy for several weeks. This galaxy is 100 million light-years from Earth.
