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The Solar System

The Solar System The Solar System consists of the Sun, the nine planets and their satellites; the comets, asteroids, meteoroids, and interplanetary dust and gas. It is composed of two systems, the inner solar system and the outer solar system. The inner solar system contains the Sun, Mercury, Venus, Earth and Mars. The outer solar system contains Jupiter, Saturn, Uranus, Neptune and Pluto. The inner planets are relatively small and made primarily of rock and iron.

The asteroids orbit the sun in a belt beyond the orbit of Mars, tumbling and sometimes colliding with one another. Made mostly of rock and iron, the asteroids may be the remnants of a planet that never formed. The outer planets, with the exception of Pluto, are much larger and made mainly of hydrogen, helium, and ice. Many astronomers believe that Pluto was and interstellar wanderer that was captured by the Suns gravity and was not an original part of the solar system. The orbits of the planets are ellipses with the sun at one focus, though all except mercury and Pluto are very nearly circular. The orbits of the planets are all more or less in the same plane that is called the ecliptic. The ecliptic is inclined only seven degrees from the plane of the ecliptic with and inclination of seventeen degrees.

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Again with the exception of Pluto, the planets all orbit the sun in almost the same plane. The average distance of the earth to the sun is used as a standard for measuring distances in the solar system and is called an astronomical unit (AU). One AU is about 93 million miles or 150 million kilometers. Mercury the planet closest to the sun is at about 0.387 AU. Pluto is the outermost planet, and it is 39.44 AU from the sun. The heilopause is the boundary between the solar system and interstellar space, and it is about 100 AU from the sun.

The comets, however, achieve the greatest distance from the Sun; they have highly eccentric orbits ranging out to 50,000 AU or more. The Sun is a regular star of intermediate size and luminosity. It is one of more than 100 billion stars in our galaxy. The Sun is by far the largest object in our solar system. The Sun is personified in many mythologies, the Greeks called it Helios and the Romans called it Sol. Sunlight and other radiation are produced by the conversion of hydrogen into helium in the Suns hot, dense interior.

The Sun is, at present, about 75% hydrogen and 25% helium by mass; everything else amounts to only 0.1%. This changes slowly over time as the Sun converts hydrogen to helium in its core. The Suns outer layers exhibit different rotation, at the equator the surface rotates once every 25.4 days: near the poles its as much as 36 days. This weird behavior is caused by the fact that the Sun is not a solid body like the Earth. The different rotation extends considerably down into the interior of the Sun but the core of the Sun rotates as a solid body.

The Suns core conditions are extreme. The pressure is 250 billion and the temperature is 15.6 million Kelvin. At the center of the core the Suns density is more than 150 times that of water. The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. For the Suns entire steadiness, it is an extremely active star.

On its surface dark sunspots bounded by intense magnetic fields come and go in 11-year cycles. Sudden bursts of charged particles from solar flares can cause auroras and disturb radio signals on Earth; and a continuous stream of protons, electrons and ions leave the Sun and move out through the solar system, spiraling with the Suns rotation. This solar wind shapes the ion tails of comets and leaves its traces in the lunar soil. The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core.

It will continue to radiate peacefully for another 5 billion years or so. But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, though commonplace by stellar standards will result in the total destruction of the Earth and probably the creation of a nebula. Today there are nine major planets in the solar system. They are currently known as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

The planet that is closest to the Sun is Mercury. It is about 36 million-miles from the Sun and its period of revolution is 88 days. Mercury is surprisingly dense, apparently because it has an unusually iron core. With only a transient atmosphere, Mercury has a surface that still bears the record of bombardment by asteroidal bodies early in its history. Mercury passes through phases similar to those of the moon as it completes each revolution around the Sun.

It has such a thin atmosphere that in a single day it reaches temperatures of up to 750*F. At night, it gets as cold as -300*F. This planet can only be seen for a short time before or after sunset. Mercury is the second smallest planet in the solar system, having a diameter of about 3,000 miles. Its mean density can compare to the earth. Its small mass and proximity to the Sun prevent it from having an appreciable atmosphere. The surface of Mercury is lots like that of the moon.

Venus is the second planet from the Sun. It is often called the Evening Star or Morning Star, and it is brighter than any object in the sky except the Sun and the moon. Venus can really never be seen much longer than 3 hrs. before or after sunrise. Venus revolves around the Sun at a distance of about 67 million miles.

Venus is often referred to as the sister planet of the Earth because it is only slightly smaller in size and mass. Venus is covered with a thick blanket of clouds that hides its surface from view. The thick atmosphere is composed mainly of carbon dioxide, with a slight amount of water vapor and some nitrogen and their elements. The high surface temperature is assumed to result partly from the greenhouse effect because it is blocked out by the top layer. Venus rotates on its axis in a retrograde direction with a period of about 243 days.

As a result of the Greenhouse effect Venus is the hottest of any planet about 477*C. Venus lies between the orbit of the Sun and Earth, so Venus passes through phases like the moon, varying from a large bright crescent (when it is close) to a silvery disk (when it is far away). Venus comes closer to the Earth than any other planet. The surface of Venus is thought to be erratic and stormy, but radio waves indicate the possibilities of two long mountain ranges. Scientists have estimated that the surface of Venus is only about 800 million years old.

Earth is the fifth largest planet and the only planet definitely known to support life. Due to gravitational forces the earth is molded into a sphe …

The Solar System

.. l planets. One being Olympus Mons, the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Like Mercury and the Moon, Mars appears to lack active plate tectonics at present; there is no evidence of recent horizontal motion of the surface such as the folded mountains so common on Earth. Jupiter Jupiter is named after the king of the Roman gods. It is the largest planet in the Solar System, the fifth planet from the Sun and the first of the outer planets Jupiter has had a dominant effect on a large part of the Solar System.

It is likely that Jupiter’s huge gravity has prevented a planet from forming in the area now occupied by the Asteroid Belt. Jupiter has a magnetic field 20,000 times stronger than that of the Earth’s, having a devastating effect on its moons. Saturn Saturn is the sixth planet from the Sun and the second largest: In Roman mythology, Saturn is the god of agriculture and has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610; he noted its odd appearance but was confused by it. Early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn’s rings every few years as Saturn moves in its orbit Like Jupiter, Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and rock, similar to the composition of the primordial Solar Nebula from which the solar system was formed. Uranus Uranus is the forth largest planet in the Solar System and the seventh from the Sun.

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Named after the father of Saturn, Uranus is a blue-green colour due to the methane in its atmosphere. Its magnetic axis is at 60 degrees to its axis of rotation. The unusual axial tilt may have been caused by a collision by a large body early in Uranus’ life. Scientists must await a new space mission. Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a 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 itself creates.


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