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How far across is the Milky Way? - Windows to the Universe

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This false-color image shows the near-infrared sky as seen by the COBE satellite. The dominant source of light at this wavelength is stars in our galaxy. So, you end up with an image that shows the thin disk and the central bulge of the Milky Way Galaxy. Our Sun lies in the plane of the disk, 28,000 light years from the center which is why the Milky Way disk appears edge-on to us.
Click on image for full size
NASA

How far across is the Milky Way?

At a given time how can one locate the center of our galaxy as we orbit the Sun and the Sun orbits the galaxy? Is our solar system moving away from the center of the galaxy? How many years does it take the Sun to orbit the center of the galaxy? Specifically, where in the universe can our solar system be found?

The Sun and our solar system are in the Milky Way galaxy. There are billions of other stars in the Milky Way Galaxy too - it's like a big star city!

Our galaxy is 90,000 light-years across. It is a spiral galaxy, so it has arms that come from the center of the galaxy like a pinwheel. The Sun is located about 28,000 light-years out from the center of the galaxy in the Orion Arm.

Our solar system is moving around the center of the galaxy. But, we don't get any closer or farther from the center of the galaxy. The solar system is moving through space really fast, but it still takes 200 million years for it to go around once!

The center of our galaxy is beyond the constellation Sagittarius. So, if you can find this constellation in the sky, you'll be looking toward the center of our galaxy! Cool!

The Milky Way is part of a set of galaxies known as the Local Group. The Local Group includes other galaxies within 3 million light-years. This Local Group is part of a supercluster, known as the Virgo supercluster. This supercluster has at least 5,000 member galaxies and is roughly 100 million light-years across. Beyond this, we don't know much about our position in the universe.

Last modified July 18, 2001 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF