Galaxies

A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle. When you look up at stars in the night sky, you're seeing other stars in the Milky Way.

Milky Way

When you look up at the night sky, assuming conditions are just right, you might just catch a glimpse of a faint, white band reaching across the heavens. This band, upon closer observation, looks speckled and dusty, filled with a million tiny points of light and halos of glowing matter. What you are seeing is the Milky Way, something that astronomers and stargazers alike have been staring up at since the beginning of time.

But just what is the Milky Way? Well, simply put, it is the name of the barred spiral galaxy in which our solar system is located. The Earth orbits the Sun in the Solar System, and the Solar System is embedded within this vast galaxy of stars. It is just one of hundreds of billions of galaxies in the Universe, and ours is called the Milky Way because the disk of the galaxy appears to be spanning the night sky like a hazy band of glowing white light.

Andromeda Galaxy

The Andromeda Galaxy is a giant swirl of around a trillion stars just down the street from the Milky Way. But billions of years from now, it will collide with our home galaxy.If you look toward the constellation Andromeda on a clear night far from city lights, you can barely make out a long, fuzzy blob called the Andromeda Galaxy. The Andromeda Galaxy, or M31, is the nearest large neighbor of our Milky Way, though it sits some 2.5 million light-years away. That makes it the most distant object regularly visible with the naked eye.

By some estimates, the Andromeda Galaxy contains roughly one trillion stars. And it stretches more than 200,000 light-years in diameter. That’s significantly bigger than the Milky Way, which more recent estimates suggest is 150,000 light-years across (though the exact boundary of where either of these galaxies "end" is a bit nebulous). Astronomers are still struggling to get an accurate count, but our galaxy also appears to have roughly a quarter to a half as many stars as Andromeda.

Planets <------------> satellites