Location and Motion of the Solar System

Where are we?

• Our solar system is located in the outer reaches of the Milky Way Galaxy, which is a spiral galaxy.

• We are located on one of its spiral arms, out towards the edge.

How many stars are out there?

• The Milky Way Galaxy contains roughly 200 billion stars.

• Most of these stars are not visible from Earth. • Almost everything that we can see in the sky

belongs to the Milky Way Galaxy.

Milky Way Stats

• 80,000 to 120,000 light-years across (and less than 7,000 light-years thick).

• The sun is about 26,000 light-years from the center of the Milky Way Galaxy,

Does it orbit?

• It takes the sun (and our solar system) roughly 200-250 million years to orbit once around the Milky Way. In this orbit, we (and the rest of the Solar System) are traveling at a velocity of about 155 miles/sec (250 km/sec).

Have we ever been out of our galaxy?

• Since we're inside the Milky Way Galaxy and we've never sent a spacecraft outside our Galaxy, we have no photographs of the Milky Way Galaxy. Radio telescope data does, however, let us know a lot about it.

Where did those crazy names come from?

• The arms of the Milky Way are named for the constellations that are seen in those directions. The major arms of the Milky Way galaxy are the Perseus Arm, Sagittarius Arm, Centaurus Arm, and Cygnus Arm; our Solar System is in a minor arm called the Orion Spur. The central hub (or central bulge) contains old stars and at least one black hole; younger stars are in the arms, along with dust and gas that form new stars.

What other galaxies are out there?

• The Milky way Galaxy is just one galaxy in a group of galaxies called the Local Group. Within the Local Group, the Milky Way Galaxy is moving about 300 km/sec (towards the constellation Virgo). The Milky Way Galaxy is moving in concert with the other galaxies in the Local Group.

Milky Way is on the move..