1 Before understanding what a satellite galaxy is, you must first understand what a galaxy is. According to NASA, “a galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity.” The galaxy that we live in is the Milky Way galaxy. Besides our galaxy, there are 10,000 galaxies that scientists know about and even more that they cannot see. These galaxies appear in many different shapes and sizes. They can be spiral, elliptical, or irregular. The Milky Way is a spiral galaxy that looks like a pinwheel, while elliptical galaxies are shaped like ovals. Irregular galaxies have no definite shape. Within a galaxy, there are several solar systems, and inside those solar systems, there are planets and stars.
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.
This question has two parts. First, answer Part A. Then, answer Part B.
Part A
How does the author develop the idea that satellite galaxies are not easily seen from Earth?
by explaining how bright the stars of the satellite galaxies are
by providing a list of the galaxies that can been seen easily from Earth
by describing the equipment necessary to see the satellite galaxies in the sky
by comparing the visibility of satellite galaxies with the visibility of other galaxies
Part B
Which statement supports the answer in Part A?
“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.” (paragraph 4)
“All three of these galaxies have very old stars that are, consequently, faint and difficult to see.” (paragraph 5)
“Other satellite galaxies orbiting the Milky Way include the Sagittarius Dwarf, the Sextans Dwarf, the Carina Dwarf, and the Fornax Dwarf.” (paragraph 6)
“Both the Carina Dwarf and Fornax Dwarf galaxies have younger stars, between three and ten billion years old. “ (paragraph 6)
1 answer
Part A:
The correct answer is by describing the equipment necessary to see the satellite galaxies in the sky. The author mentions that many satellite galaxies are faint and difficult to see without special equipment, indicating that they are not easily visible from Earth.
Part B:
The statement that supports the answer in Part A is “All three of these galaxies have very old stars that are, consequently, faint and difficult to see.” (paragraph 5). This statement reinforces the idea that satellite galaxies have characteristics (old stars) that make them hard to observe, aligning with the point made in Part A regarding the need for special equipment to see them.
1 answer