What are Galaxies?
Galaxies are sprawling space systems composed of dust, gas, and countless stars. The number of galaxies cannot be counted—the observable universe alone may contain 100 billion. Some of these distant systems are similar to our own Milky Way galaxy, while others are quite different.
Galaxies with less than a billion stars are considered “small galaxies.” In our own galaxy, the sun is just one of about 100 billion stars.
Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies.1
Also, it should be mentioned that radio galaxies are a type in their own right. Though radio galaxies fall into any of the three general types listed above, something about them makes them different. More on that later.
M101 (pictured below) is a majestic example of a spiral galaxy.
Click here for a great gallery of spiral galaxies!
Centaurus A (pictured below) is one of my personal faves and it is a beautiful example of elliptical galaxies. It is also an example of a radio galaxy: galaxies known for their luminosity at radio wavelengths.
Click here for a gallery of elliptical galaxies.
NGC 1427A is an example of an irregular galaxy.
Bonus: Listen to Carl Sagan talk about galaxies! (See Here)