The Milky Way Galaxy
2 So what is a satellite galaxy?
3 In a solar system, moons circle around planets, and planets circle around large stars. In the Milky Way, Earth and other planets orbit the Sun. The Sun, in turn, orbits the center of the galaxy. These moons, planets, and Sun are all satellites because they orbit around something larger than themselves. A satellite galaxy, then, is a galaxy that circles a larger galaxy. Scientists now believe there are around sixty satellite galaxies that orbit the Milky Way. Twelve of them have been named and studied.
4 Two of these include the Large Magellanic Cloud and the Small Magellanic Cloud named after Ferdinand Magellan, who discovered them. As their names suggest, the Large Magellanic Cloud is bigger than its counterpart. However, the Small Magellanic Cloud is an irregularly shaped galaxy and is still pretty large. Like many satellite galaxies, these two are considered dwarf galaxies, which means they are smaller galaxies, unlike the Milky Way. The Large Magellanic Cloud, also an irregular shape, is the largest of the known Milky Way satellites. It is one of the only satellite galaxies that can be seen in the skies without the use of special equipment and can only be seen in the skies of the Southern Hemisphere.
5 Some of the earliest satellite galaxies discovered are the Sculptor Dwarf (1937), the Ursa Minor Dwarf (1954), and the Draco Dwarf (1954). All three of these galaxies have very old stars that are, consequently, faint and difficult to see. Although discovered much more recently in 2006, the Bootes Dwarf galaxy is also very difficult to see. In fact, it is one of the dimmest of the galaxies scientists know about.
6 Two other galaxies discovered in the mid-2000s, the Ursa Major I and Ursa Major II, are both elliptical and are also some of the dimmest galaxies, unable to be seen by a typical photograph. Other satellite galaxies orbiting the Milky Way include the Sagittarius Dwarf, the Sextans Dwarf, the Carina Dwarf, and the Fornax Dwarf. The Sagittarius Dwarf galaxy is the closest satellite to the Milky Way. Interestingly, because of its closeness, the gravitational pull of the Milky Way galaxy is tearing the Sagittarius Dwarf galaxy apart. The Sextans Dwarf galaxy is larger than some of the galaxies that are difficult to see but is just as difficult to see. Both the Carina Dwarf and Fornax Dwarf galaxies have younger stars, between three and ten billion years old.
7 So why are satellite galaxies important? Besides being interesting, scientists believe that by studying these satellite galaxies, they can learn more about dark matter, which is matter in space that does not produce light or energy. They also hope to learn about how galaxies form and what role dark matter may play in this formation. Not only this, but because of the gravitational pull of the Milky Way, scientists believe that eventually our galaxy will absorb these galaxies as part of our own. This is one way they believe galaxies are able to become larger.
What does the comparison in paragraph 6 between the Pacific and Atlantic Oceans reveal about why Magellan gave the Pacific its name?
A. that the fighting among the sailors finally ended once they found the strait
B. that finding what the sailors had been looking for allowed them to finally rest
C. that leaving the Atlantic Ocean offered an end to the hardships the sailors had suffered on the voyage
D. that the waters of the Pacific Ocean were not as stormy and harsh as those the sailors had faced in the Atlantic
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The comparison in paragraph 6 between the Pacific and Atlantic Oceans reveals that Magellan gave the Pacific its name because:
D. that the waters of the Pacific Ocean were not as stormy and harsh as those the sailors had faced in the Atlantic.
This interpretation is based on the implication that the sailors experienced difficulties and storms in the Atlantic, and upon entering the Pacific, they found calmer waters, which led to the naming.
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