The Solar System Essay Research Paper Assignment — страница 3

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little helium (in contrast to Jupiter and Saturn which are mostly hydrogen). Neptune Neptune – named after the Roman god of the sea – was discovered using mathematic calculations based on the orbit of Uranus. It is the third largest planet in the Solar System and is usually the second last planet in distance. Because of Pluto’s eccentic orbit, Neptune is the last planet for 20 years every 247 years. Neptune was the last planet until recently, when Pluto past it with its orbit and became the last planet again. Pluto Pluto was discovered on February 18, 1930, making it the last planet found in our Solar System. Pluto is usually farther from the Sun then any of the nine planets. Ground-based observations indicate that Pluto’s surface is covered with methane ice and that

there is a thin atmosphere that might freeze and fall to the surface as the planet moves away from the Sun. Pluto has one moon – Charon – its surface composition seems to be different from Pluto’s. The moon appears to be covered with water-ice rather than methane ice. Its orbit is gravitationally locked with Pluto, so both bodies always keep the same hemisphere facing each other. Asteroids Asteroids are rocky and metallic objects that orbit the Sun but are too small to be considered planets. They are known as minor planets. Asteroids range in size from Ceres, which has a diameter of about 1000 km, down to the size of pebbles. Sixteen asteroids have a diameter of 240 km or greater. They have been found inside Earth’s orbit to beyond Saturn’s orbit. Most, however, are

contained within a main belt that exists between the orbits of Mars and Jupiter. Asteroids are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago. Meteors and Meteorites The term meteor comes from the Greek ?meteoron?, meaning phenomenon in the sky. A meteoroid is matter revolving around the sun or any object in interplanetary space that is too small to be called an asteroid or a comet. A meteorite is a meteoroid that reaches the surface of the Earth without being completely vaporized. Meteorites have proven difficult to classify, but the three broadest groupings are stony, stony iron, and iron. The most common meteorites are chondrites, which are stony meteorites.

Radiometric dating of chondrites has placed them at the age of 4.55 billion years, which is the approximate age of the solar system. Comets Comets are small, fragile, irregularly shaped bodies composed of a mixture of non-volatile grains and frozen gases. They have highly elliptical orbits that bring them very close to the Sun and swing them deeply into space, often beyond the orbit of Pluto. Comet structures are diverse and very dynamic, but they all develop a surrounding cloud of diffuse material, called a coma, that usually grows in size and brightness as the comet approaches the Sun. As comets approach the Sun they develop enormous tails of luminous material that extend for millions of kilometers from the head, away from the Sun. History Traditionally histories of Astronomy

usually begin with the Greeks. The Greek philosopher Aristotle held that the earth is fixed at the center of the universe while Ptolemy based a mathematical model of the moving planets in our Solar System. Nicolaus Copernicus, in 1543, published his hypothesis that the sun is the center of the universe but since the teaching of Aristotle had been adopted by the church his view was seen as unbelievable. 1609 A.D. Five years after the appearance of the great supernova of 1604, Galileo builds his first telescope. He sees the moons of Jupiter, Saturn’s rings, the phases of Venus, and the stars in the Milky Way. He publishes the news the following year in “The Starry Messinger”. 1665 A.D. At the age of 23, young Isaac Newton realizes that gravitational force accounts for falling

bodies on earth as well as the motion of the moon and the planets in orbit. This is a revolutionary step in the history of thought, as it extends the influence of earthly behavior to the realm of the heavens. One set of laws, discovered and tested on our planet, will be seen to govern the entire universe. 1905 A.D. The first of his many seminal contributions to twentieth century science, relativity recognizes the speed of light as the absolute speed limit in the universe and, as such, unites the previously separate concepts of space and time into a unified spacetime. Eleven years later, his General Theory of Relativity replaces Newton’s model of gravity with one in which the gravitational force is interpreted as the response of bodies to distortions in spacetime which matter