Monday Astronomy Picture Ponderings (MAPPs) 6/20/2022
Spiral, Elliptical, and Irregular Galaxies, Oh My!
Welcome back to the Monday Astronomy Picture Ponderings (MAPPs) series where every Monday I normally pick one of NASA’s Astronomy Picture of the Day (APOD) entries from the past seven days to focus on in some way.
On June 13th, 2022, NASA’s Astronomy Picture of the Day featured an absolutely beautiful copyrighted image of M51, the Whirlpool Galaxy from the Hubble Space Telescope. I’ve featured galaxies before in this series and wanted to take this opportunity to give a nice overview of galaxies, including how you can learn more about them and even contribute to scientific research.
Since the image is copyrighted and the creators deserve credit for their work, I encourage you to check out the link above to see the image featured on the 13th, but for this article, we will be utilizing galaxy images from Astropix, an amazing repository of free-to-use images from some of the best telescopes around the world.
What is a galaxy?
“Galaxies are vast cosmic islands of stars, gas, dust, and dark matter held together by gravity.” — Galaxies, NASA Hubblesite
I love the quote above, but we need more info, don’t we? How big are they? What’s the closest one to us? How do they compare to other common astronomical objects?
Very simply, if we use Earth as our starting point, Earth is one of 8 planets in our Solar System which contains our Sun (the star of this system) and the astronomical bodies that are caught within its orbit including planets, moons, dwarf planets, asteroids, and comets. Our Sun is just one of the billions, hundreds of billions of stars within our own Milky Way Galaxy, which is about 100,000 lightyears across.
But the Milky Way Galaxy is not alone. There are also billions upon billions of galaxies in the universe. The Milky Way is part of the Local Group Cluster of galaxies, which is in turn part of a supercluster of galaxies, which is part of a supercluster complex, which is one filament of the universe.