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Galaxies [Questions 12-19]

12. What are the nearest galaxies to our own Milky Way Galaxy?

The nearest galaxies to our Milky Way Galaxy is the Local Group.

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13. What kind of galaxy do we live in?

The Milky Way Galaxy is probably a spiral galaxy with two arms. If we were to see it from a great distance in space, it might look very much like the Great Spiral Galaxy in Andromeda.

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14. How big is our Galaxy?

The Milky Way Galaxy is estimated to have a diameter of about 100,000 light years and to have a thickness, or depth of about 20,000 light years. It has a stellar population of about 100 milliard stars and contains additional dust and gas - about 10% of the total mass of the galaxy. Most of the dust and gas is concentrated in the arm structure, where it may amount about 50% of the mass of the arms.

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15. Is our Galaxy in motion?

It is rotating about a point at its centre. The rotation of the Galaxy is not uniform like the solar system where we are. The rotation of the Galaxy carries our Sun and us about the centre in about 225 million years. At about half the distance from the centre to the Sun, the rotation is faster, carrying the stars around in less than half that time. The rotation is complex, however, and takes a rather different form near the centre.

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16. How fast does our Galaxy rotate?

The Milky Way Galaxy is rotating at about 240 kilometers per second at the distance from the centre at which our Sun is located. The rotation of stars nearer the centre will be faster, while those farther from the center will be rotating more slowly. The Sun will travel completely around the centre of the galaxy in about 225 million years.

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17. Just where are we inside our Galaxy?

We are in the plane of the disk of our Galaxy and about 1/3 the distance between one edge and the centre of the Galaxy - about 15,000 light years from the edge and about 30,000 light years from the centre.

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18. Can we see from the Earth any trace of the structure of our Galaxy?

Yes, the Milky Way, a band of faint luminosity that crosses overhead in summer and in winter, but which is not so high in spring nor in autumn, is our view of the disk of our own Galaxy. Through the telescopes we can see that the Milky Way is made up of countless stars. This is the edge of our Galaxy, seen from our position inside the Galaxy. The edge of our Galaxy nearest us lies in Taurus, and in Sagittarius.

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19. If we are nearer to one edge of our Galaxy, what difference does our position make in what we can see of the Galaxy?

Our location almost in the plane of the Galaxy, makes some difference in what we see of the Milky Way. A much greater difference, however, is because of the different structure of the Milky Way itself. Through Taurus, the Path of the Milky Way is much fainter and more diffuse than through the region opposite, in Sagittarius. We see more light from the Milky Way in Sagittarius because there are more stars there giving the light we see. There is also much more gas and dust in the direction of Taurus, so the contrast is not so great as it would be if we could see equally well in both directions. The star clouds in Sagittarius are much brighter than they appear to us.

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20. Is there much chance of galaxies' colliding?

Yes. In the average region of space, galaxies collision occur every three million years. There are an estimated two thousand galaxies in the volume of space which extends out to 250 million light years from us. The motion of these galaxies would bring about ten collisions continually plus calculating a collision to occur even when the outermost region of two galaxies are in contact. There are regions in space where galaxies are closely clustered and collision must be even more often.

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21. Can a galaxy suffer more than one collision?

In clusters of galaxies, more than one collision is possible. In the cluster of galaxies lying in the constellations of Coma Berenices and Virgo, known as the Coma cluster, it has been believed that some of galaxies may have undergone between five and thirty different collisions during the estimated life of the Universe.

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22. What are the Magellanic Clouds? Have they any other name?

The Magellanic Clouds are small, irregular galaxies, and are the nearest of the outer galaxies to our own Milky Way Galaxy. They appear as two rather hazy, luminous clouds not far from the south celestial pole, they can be seen only from points on the surface of the Earth south of 20 north latitude. These clouds were first reported by the men of Magellan's voyage around the Earth in 1516. Their formal astronomical names are Nubecula Major for the large cloud and Nubecula Minor for the small cloud. Nubecula is Latin for "a little cloud".

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See also
• The Sun
• The Earth
• The Moon
• Mercury, Venus and Mars
• Jupiter, Saturn, Uranus, Neptune, Pluto
• Meteors and Comets
• Stars
• The Constellations
• Scientists and Astronomers

Related Internet Links
• Classifying Galaxies
• Arp's Catalog Of Galaxies
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