六级冲刺备考阅读练习（22）

　　Our galaxy is a gigantic agglomeration of stars and planets whose numbers will probably never been known. Currently we estimate this number to be about thirty billion. Scientists have estimated that the diameter of our galaxy, if it were to be traveled, would take us about fifty thousand light years and the thickness to be about fifteen to twenty light years.

　　We live in small part of the Milky Way Galaxy, which is referred to as a solar system. Our solar system is made up of nine planets and 31 moons, which orbit the center of galaxy. At the center of our galaxy is our Sun, which is approximately twenty-five thousand light years from our solar system.

　　These nine major planets in order from the center are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

　　Mercury is the planet nearest to the Sun. As it orbits the Sun, it does not rotate, keeping the same face of the planet toward the Sun at all times. This means that one side of the planet has a continual burning day of 900 F, and the other side a continual night and a deadly cold of 450 F below zero. Mercury is the fastest traveling of the nine planets making one full orbit around the Sun in only eight days. Life on mercury would be impossible. If you could live where the night meets the day and survive the extreme conditions, you would need dark goggles to protect you eyes from the extreme light. Mercury has little or no atmosphere to diffuse the sunlight. You would also weigh considerable less due to the lack of gravity. A person weighting 100 pounds on Earth would weigh 27 pounds on Mercury.

　　Looking into the night sky you will notice Venus, the brightest star in the sky, and the second planet from the Sun. Venus can only be seen at certain times of the day either at dawn or at Sunset. In physical characteristics, Venus is most like earth with a diameter of seven thousand six hundred miles, and gravity the same as earth. It is located a distance of sixty-seven million miles from the Sun and makes one complete orbit around the Sun in two hundred twenty five days. A single day on Venus can last up to two hundred and twenty five earth days due to its slow rotation. The atmosphere appears to consist of mostly nitrogen and carbon dioxide. This is due to the lack of life on the planet.

　　The best time to view Venus comes every one hundred and twenty years as it passes between the Earth and the Sun. The last time to best view it was on June 7, 2004.

　　Earth, the third planet form the Sun is our home planet. Earth is the only planet in our solar system known to sustain life. Under the layer of atmosphere that surrounds the planet we are able to provide all the necessary components to make life sustainable. Earth is the fifth larges planet in the solar system. Its diameter is just a few hundred kilometers larger than Venus. Earth rotates on its axis one complete revolution in a twenty-four hour period and orbits the Sun in three hundred and sixty five days.

　　Mars is the fourth planet from the Sun and is the closest neighbor to earth. Every seventeen years Mars reaches its closest point to earth in its orbit around the Sun at thirty-five million miles.

　　Mars is a small planet that has a red glow. It makes one complete orbit around the Sun in six hundred and eighty seven days. Oxygen and water vapor have been detected in the atmosphere of Mars, and a yellowish fog and clouds move around the planet indicating that the planet has different types of weather and seasons like the earth. A single day on Mars is very much like a day on earth lasting twenty-four hours and thirty-seven minutes, however, a year on Mars is twice as long as one year on earth.

　　Jupiter the fifth planet from the Sun gets its name from the Father of the Greek Gods. Jupiter, which orbits four hundred eighty-three million miles from the Sun, is the biggest of all the planets in our solar system. It has a diameter of eighty-nine thousand miles and a volume of thirteen times that of earth. Jupiter orbits the Sun every twelve years. Its atmosphere is thousands of miles thick and is made up of mainly hydrogen. The surface temperature is about -205 F. There are no seasons on Jupiter, but it has floating clouds of ammonia and methane gas.

　　Jupiter has a bright red distinctive spot that is more than twice as wide as Earth. This mark has astronomers puzzled because there is no reason for the bright spot due to the fact that it does not receive much Sunlight. This spot enables us to see that Jupiter has a very fast rotation. One rotation is completed every ten hours. The forces placed on the planet due to this quick rotation cause the clouds at the equator to bulge like a tire, but due to the gravitational forces of the planet keep the clouds from being cast into space.

　　Saturn, even though it is the sixth planet form the Sun, it shines so brightly because of its size. Its diameter is seventy-one thousand five hundred miles. The planet itself is golden in color and is the brightest yellow star in the night sky.

　　Saturn makes one complete revolution on its axis every ten hours and takes twenty-nine and one half days to complete one orbit around the Sun. The gravitational pull of this planet is most like that of Jupiter. It has a volume that is eight hundred times that of earth, but has a volume that is one hundred times lighter than earth.

　　Saturn has two rings that surround the planet, but never touch it. They are located outside the atmosphere and above the equator. These rings are only about ten miles thick, which makes them transparent, only being seen with the use of a telescope. The ring closest to the planet is about seven thousand miles and very thin. A black band separates the inner ring from the outer ring, which is wider and brighter. It is believed that the rings are made up of crystals of ice or dust particles.

　　Uranus is the seventh planet form the Sun. The name Uranus comes from Greek mythology. Uranus was the God of the Heavens.〃

　　Uranus is situated one thousand seven hundred and eighty two miles form the Sun and completes one orbit around the Sun every eighty-four years. The size of this planet is four times that of earth, but has the same force of gravity on the surface as earth. There are five moons that orbit this planet. The largest one is Titania.

　　Neptune, the eighth planet from the Sun, is invisible to the naked eye. It is located some two thousand seven hundred and ninety-three million miles form the Sun. A single orbit around the Sun takes one hundred and sixty-five yeas to complete. This planet only receives one nine-hundredth of the heat and Sunlight as the earth.

　　Pluto was the ninth planet from the Sun. The name Pluto comes from the Roman God who was the ruler of the under world. On Thursday, August 24, 2006, however, the International Astronomical Union met in Prague voted finalizing the guidelines of planetary classification, thus reorganizing Pluto into a new category of dwarf planet .

　　Pluto is located three thousand six hundred and seventy million miles form the Sun. It orbits the Sun in total darkness, and is about the same size as Mars and has a diameter two thirds that of Earth s moon. Due to the distance and size of Pluto, it can only be seen with the use of a twenty-inch telescope.

　　Pluto disqualified due to its eccentric orbit that crosses with Neptune. In addition to the fact that it is disproportionately smaller than any of its former counterparts in the solar system, it does not qualify as a planet. Otherwise, we might as well qualify Pluto s moon, Charon as a planet, thus making Pluto and Charon a binary planet system.