Milky Way
Photo courtesy of SEDS

by Chelsie MacKenzie and Lacey Gordon

It wasn't until this century that astronomers really understood the nature of the galaxy that surrounds us, the Milky Way. The Milky Way Galaxy is like a big, translucent pancake. Our Solar System is in it about halfway from the middle to the edge on one side. The big strip you see in the sky as the Milky Way is the light from many of the stars in our disk shaped galaxy. The Milky Way seems to wrap around the whole sky because of the pancake shape that surrounds us. But because of all the gas and dust in the galaxy, it is not transparent, so we can only see about 5% to 10% of the way across with visible-light telescopes; however, radio and infrared telescopes can see farther through the dust. The Milky Way appears about equally bright in a band around the sky.

The Milky Way is a spiral galaxy which formed about 14 billion years ago, and looks like a large pinwheel rotating in space. Dust, gas and stars fan out from the center of the Milky Way in long spiraling arms. Our galaxy is made of clouds of dust and gas called nebula, stars, comets, meteors, asteroids, and planets. Our own Sun and Solar System also are a part of the Milky Way Galaxy; our Solar System is about 26,000 light-years from the center of the Galaxy. The Sun travels around the center of the Milky Way, taking about 250 million years to complete an orbit. All objects in the Milky Way rotate around the Galaxy's center. The Milky Way is about 100,000 light-years in diameter. A typical spiral galaxy, the Milky Way includes at least 100 billion stars in its diameter.

Those of us who live in the northern hemisphere cannot see the two closest galaxies, which are rather like two satellite galaxies to the Milky Way. All of the stars that you see with the naked eye on any given night belong to the Milky Way. The stars in the Milky Way can be easily seen with binoculars. From a really far distance and dark location, the Milky Way is even bright enough to cast shadows.

Bibliography and Additional Sources of Information

Classifying Galaxies.

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