The Milky Way is a barred spiral galaxy, one of hundreds of billions in the observable universe.

However, multiple lines of evidence — most importantly, that material in the galaxy orbits the center far too quickly to be held together by the gravity of visible objects — suggest that most of the mass of the Milky Way is made up of some form of matter that does not interact with light.

However, in the early 1920's, astronomer Edwin Hubble made detailed observations of the Andromeda Nebula, revealing that it was its own "island" of stars — a galaxy in its own right — located millions of light-years away from us, according to Britannica.

When we are looking in the direction of the disk, Earthlings see the combined light of all the stars in the galaxy.

When we look in a direction away from the disk, we see only the stars close to our solar system.

At the very center of the galaxy sits Sagittarius A*, a supermassive black hole with a mass that's 4.1 million times that of the sun, according to the UCLA Galactic Center Group.

The stellar disk of the Milky Way has a radius of 75,000 to 100,000 light-years, but it is only about 1,000 light-years thick.

Our nearest neighbor is the Andromeda galaxy, located about 2.5 million light-years away.

Together with Andromeda and about 80 smaller galaxies, the Milky Way is a part of the Local Group, which is a group of galaxies, about 10 million light-years across, bound together by their common gravity, according to Swinburne University.

At the center of this supercluster sits the Virgo Cluster, a massive collection of 1,000 to 2,000 galaxies about 54 million light-years away.

Most of that mass, by far, is in the form of dark matter; stars represent around only 1% of the mass of the galaxy, and interstellar gas accounts for only 0.1%.

Our galaxy is on a collision course with Andromeda, and our two galaxies will crash and begin to merge in about 5 billion years.