A galaxy is a large group of stars, gas, and dust bound together by gravity. All the stars we see in the night sky are in our own Milky Way Galaxy.
Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area.
It is very difficult to count the number of stars in the Milky Way from our position inside the galaxy. Our best estimates tell us that the Milky Way is made up of approximately 100 billion stars. These stars form a large disk whose diameter is about 100,000 light years.
Our Solar System is about 25,000 light years away from the center of our galaxy we live in the suburbs of our galaxy.
Just as the Earth goes around the Sun, the Sun goes around the center of the Milky Way. It takes 250 million years for our Sun and the solar system to go all the way around the center of the Milky Way.
At the very center of the Milky Way Galaxy is a supermassive black hole called Sagittarius A. It has about 4 million times the mass of the Sun.
There are thought to be four spiral arms that all start near the Milky Way Galaxy’s center.
- Near 3kpc Arm and Perseus Arm
- Norma Arm and Outer Arm
- Far 3kpc and Scutum-Centaurus Arm
- Sagittarius Arm
- Orion Arm or Orion–Cygnus Arm
Alpha Centauri is the closest known star system to the Solar System.
The closest star in the group is Proxima Centauri, located only 4.243 light-years from the Sun. And then the Alpha Centauri A/B stars are located 4.37 light-years away.