Page 23 - Life beyond the Karman

Galaxies
A galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of shapes and sizes. However, four main shapes are mostly recognised in the sky, namely:
• A spiral galaxy;
• A barred spiral galaxy;
• An elliptical galaxy;
• An irregular galaxy.
The Milky Way galaxy
Our sun (a star) and all the planets around it are part of a galaxy known as the Milky Way. The Milky Way is a large barred spiral galaxy.
All the stars we see in the night sky are in our Milky Way Galaxy. It 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. These stars form a large disk whose diameter is about 100,000 light years.
Just as the Earth goes around the sun, the sun goes around the centre of the Milky Way. It takes 250 million years for our sun and the solar system to go all the way around the centre of the Milky Way.
We can only take pictures of the Milky Way from inside the
galaxy, which means we don’t have an image of the Milky Way as a whole. Why, then, do we think it is a barred spiral galaxy? There are several clues.
The first clue to the shape of the Milky Way comes from the bright band of stars that stretches across the sky. This can be seen with the naked eye in places with dark night skies. It comes from seeing the disk of stars that forms the Milky Way from inside the disk.
Several different telescopes, both on the ground and in space, have captured images of the disk of the Milky Way by taking a series of pictures in different directions.
Types of active galaxies:
• Radio galaxies;
• Seyfert galaxies;
• Quasars;
• Blazars.
Radio galaxy
LIFE BEYOND THE KÁRMÁN LINE - OUTER SPACE
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