milky way

shape and size

Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it, astronomers have identified it as a typical spiral galaxy containing about 200 billion to 400 billion stars (Figure 1.1). An artists rendition of what astronomers think the Milky Way Galaxy would look like seen from above. The Sun is located approximately where the arrow points. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms. The disk is about 100,000 light- years across and 3,000 light-years thick. Most of the Galaxys gas, dust, young stars, and open clusters are in the disk. What evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy? 1. The shape of the galaxy as we see it (Figure 1.2). 2. The velocities of stars and gas in the galaxy show a rotational motion. 3. The gases, color, and dust are typical of spiral galaxies. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Astronomers have discovered that there is a gigantic black hole at the center of the galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxys disk would still be An infrared image of the Milky Way shows the long thin line of stars and the central bulge typical of spiral galaxies. wider than the entire United States!

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the milky way galaxy

The Milky Way Galaxy, which is our galaxy. The Milky Way is made of millions of stars along with a lot of gas and dust. It looks different from other galaxies because we are looking at the main disk from within the galaxy. Astronomers estimate that the Milky Way contains 200 to 400 billion stars.

where we are

Our solar system, including the Sun, Earth, and all the other planets, is within one of the spiral arms in the disk of the Milky Way Galaxy. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are about 26,000 light-years from the center of the galaxy, a little more than halfway out from the center of the galaxy to the edge. Just as Earth orbits the Sun, the Sun and solar system orbit the center of the Galaxy. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. Astronomers have recently discovered that at the center of the Milky Way, and most other galaxies, is a supermassive black hole, although a black hole cannot be seen. This video describes the solar system in which we live. It is located in an outer edge of the Milky Way galaxy, which spans 100,000 light years. Click image to the left or use the URL below. URL: The Universe contains many billions of stars and there are many billions of galaxies. Our home, the Milky Way galaxy, is only one. Click image to the left or use the URL below. URL:

instructional diagrams

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questions

astronomers estimate that the milky way contains ___.

a) 100 to 200 billion stars

-->  b) 200 to 400 billion stars

c) 400 to 600 billion stars

d) 600 to 800 billion stars

the milky way galaxy is a(n) _____.

a) elliptical galaxy

b) irregular galaxy

c) circular galaxy

-->  d) spiral galaxy

the central bulge of our galaxy

-->  a) contains mostly older stars and globular clusters.

b) is most likely to be spherical in shape.

c) is only a few light years wide.

d) all of the above.

in the center of the milky way galaxy is a

-->  a) black hole

b) neutron star

c) supernova

d) nebula

what is the evidence that the milky way is the type of galaxy that astronomers think it is?

a) the shape as we see it.

b) the rotational motion.

c) the gases, color and amount of dust.

-->  d) all of the above.

one orbit of our solar system around the center of the galaxy takes about ___.

a) 225 to 500 years

b) 225,000 to 250,000 years

-->  c) 225 to 250 million years

d) 250 to 275 billion years

the solar system formed 4.6 billion years ago.

-->  a) true

b) false

our solar system is

a) very near the center of the galaxy.

-->  b) about half way out one of the spiral arms of the galaxy.

c) just outside the galaxy.

d) none of the above.

in our best spacecraft, how long would it take us to get to the center of the milky way galaxy?

a) 26,000 years

-->  b) 26,000 light years

c) 225 million years

d) 225 million light years

the milky way galaxy formed 4.6 billion years ago.

a) true

-->  b) false

diagram questions

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