The Earth and the Solar System is located within the Milky Way, so it’s kind of difficult to figure out where is Earth in the Milky Way. In fact, astronomers have only realized that the Milky Way is actually the disk of our galaxy, and not a vast nebula or collection of stars. Astronomers have only really know that there are other galaxies for less than a century.
The Milky Way is a barred spiral galaxy that measures about 100,000 light-years across, and is thought to contain between 100 and 400 billion stars. The Solar System (and Earth) is located about 25,000 light-years to the galactic center and 25,000 light-years away from the rim. So, imagine a dinner plate as the Milky Way, and draw an imaginary line from the center of the plate to the outside. We’re located about halfway along that line.
Astronomers have recently agreed that the Milky Way probably has two major spiral arms – Perseus arm and the Scutum-Centaurus arm – with several smaller arms and spurs. The Solar System is located in a region in between the two arms called the Orion-Cygnus arm. This arm measures 3,500 light-years across and is 10,000 light-years in length, where it breaks off from the Sagittarius Arm.
You might be surprised to learn that it takes the Sun 250 million years to complete one rotation around the Milky Way. The last time the Solar System was in this position in the Milky Way, there were dinosaurs on Earth.
We’ve also recorded an episode of Astronomy Cast all about the Milky Way. Listen here, Episode 99: The Milky Way.