There are billions of other galaxies in the Universe. All of this adds up to give us a picture of the Milky Way, even though we can't get outside to see the whole thing. Astronomers measure the amount of dust in the Milky Way and the dominant colors of the light we see, and they match those we find in other typical spiral galaxies. Robert Hurt, the Spitzer Science Center Robert Benjamin)Īdditional clues to the spiral nature of the Milky Way come from a variety of other properties. This artist's conception of the Milky Way's spiral structure is based on the measured distances of young, hot stars (shown in red) and ionized clouds of hydrogen gas (shown in blue). Since we can't get outside the Milky Way, we have to rely on markers of spiral arms like young, massive stars and ionized clouds. If we lived in an elliptical galaxy, we would see the stars of our galaxy spread out all around the sky, not in a single band. The concentration of stars in a band adds to the evidence that the Milky Way is a spiral galaxy. Several different telescopes, both on the ground and in space, have taken images of the disk of the Milky Way by taking a series of pictures in different directions a bit like taking a panoramic picture with your camera or phone. That band comes from seeing the disk of stars that forms the Milky Way from inside the disk, and tells us that our galaxy is basically flat. This band of stars can be seen with the naked eye in places with dark night skies. The first clue to the shape of the Milky Way comes from the bright band of stars that stretches across the sky (and, as mentioned above, is how the Milky Way got its name). Why do we think it is a barred spiral galaxy, then? There are several clues. We can only take pictures of the Milky Way from inside the galaxy, which means we don't have an image of the Milky Way as a whole.
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