سؤال قراءة ستيب محلول — فهم التفاصيل (تدريب 6651)

(1) In a very rough sense, you could think of the solar system as your house or apartment and the Galaxy as your town, made up of many houses and buildings. In the twentieth century, astronomers were able to show that, just as our world is made up of many, many towns, so the universe is made up of enormous numbers of galaxies. (We define the universe to be everything that exists that we can see.) Galaxies go as far into space as our telescopes can see and many billions of them within the reach of modern instruments. When they were first discovered, some astronomers called galaxies island universes, and the term is very appropriate because galaxies do look like islands of stars in the enormous, dark seas of empty space. (2) The nearest galaxy, discovered in 1993, is a small one that lies 75,000 light-years from the Sun in the direction of the constellation Sagittarius, where the light in our own Galaxy makes it especially difficult to see. (A constellation, we should note, is one of the 88 sections into which astronomers divide the sky, each named after an important star pattern within it.) Beyond this Sagittarius dwarf galaxy lie two other small galaxies, about 160,000 light-years away. First recorded by Magellan’s crew as he sailed around the world, these are called the Magellanic Clouds. All three of these small galaxies are satellites of the Milky Way Galaxy, interacting with it through the force of gravity. In the end, all three may even be swallowed by our much larger Galaxy, as other small galaxies have been over the course of cosmic time. (3) The nearest large galaxy is a quite similar to our own, located in the constellation of Andromeda, and is thus called the Andromeda Galaxy Andromeda Galaxy. It is also known by one of its catalog numbers, M31. This galaxy is a little more than 2 million light-years away and, along with the Milky Way, is part of a small cluster of more than 50 galaxies, which is called the Local Group. (4) At distances of 10 to 15 million light-years, we find other small galaxy groups, and then at about 50 million light-years there are much bigger systems with thousands of member galaxies. We have discovered that galaxies occur mostly in clusters, both large and small. (5) Some of the clusters themselves form into larger groups called superclusters. The Local Group Local Group is part of a supercluster of galaxies, called the Virgo Supercluster, Virgo Supercluster, which stretches over a diameter of 110 million light-years. We are just beginning to explore the structure of the universe at these enormous scales and are already learning many new things. (8) How far is the nearest galaxy from the sun?