Sunday, 11 November 2012
Comets are small pieces of ice and dust that orbit around the Sun, but their paths are not like those of the planets. Most comets spend much of their time out of the Solar System, beyond Pluto. However, they can enter new orbits that bring them into the Solar System where they become visible from Earth. The most famous comet is called Halley's comet which returns to the center of the Solar System Every seventy-six years. Halley's comet was last seen in early 1986. It will not be seen again until its return in 2061. Halley was the first astronomer to show that some comets followed orbits that keep returning them to the vicinity of the Sun.
Meteoroids are small pieces of rock or metal floating in outer space. When meteoroids float near to the Earth, they may be drawn into the Earth's atmosphere due to gravity. Meteoroids which enter the Earth's atmosphere are called meteors. Most meteors will burn up when they enter the Earth's atmosphere due to friction. Thus, streaks of light can be seen in the sky at night in the dark. They leave behind fiery tails and are called shooting stars. Meteors which do not burn completely and reach the Earth's surface are called meteorites. Meteorites which fall to the ground will make huge craters. One such crater is found in Arizona, the United State of America. many of the planets and their natural satellites are covered with meteorite craters. However, the Earth does not have many meteorite craters since it is protected by its atmosphere.
|Huge craters in Arizona, the United State of America|
Saturday, 10 November 2012
Natural satellite are the natural objects which orbit around planets. The Moon is the Earth's only natural satellite. All the planets in the Solar System have natural satellites except Mercury and Venus.
|The asteroid belt|
Besides the eight planets there is also an asteroid belt. The asteroid belt lies between the orbits of Mars and Jupiter. Asteroids are small pieces of rocks mixed with metals orbiting round the Sun. Asteroids vary in size. Some can be as small as dust particles while some can be a few hundred kilometers in diameter.
Pluto Kuiper Belt
Pluto, a dwarf planet, is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion. The Kuiper Belt, is a distant region of the Solar System beyond the orbit of Neptune. It consists of thousands of icy objects with diameters of at least 1000 km that were formed early in Solar System history.
|The Solar System|
The Constituents of the Solar System
The Solar System consists of eight planets and the Sun. The other members of the Solar System are natural satellites, asteroids, comets and meteoroids. The eight planets in the Solar System beginning with the nearest to the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All the eight planets are moving around the Sun each following its own oval path called orbit. On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet. The time taken for a planet to complete one revolution around the Sun is different from the time taken for another planet to do so.
Mercury is the closest planet to the Sun. Since Mercury is closest to the Sun its temperature can be over 300oC in the daytime. Mercury rotates on its own axis very slowly, making one full rotation every 59 Earth days.
Venus is the second planet from the Sun. The size of Venus is about the same as that of the Earth. The planet is always covered by a very thick cloud of carbon dioxide and acid vapour. Thus, the temperature of Venus is extremely hight, even though Venus is twice as far from the Sun as Mercury and receives only a quarter as much light. As a result, the surface temperature can be above 450oC. Venus takes about 225 days to revolve around the Sun. It rotates on its own axis once every 243days. Its gravity is the same as that of the Earth.
Earth is the third planet from the Sun. It is the fifth largest planet. It is the only planet with oxygen and water. Thus, it is the only planet on which living things can survive and grow. Earth takes about 365 days to revolve around the Sun and rotates on its own axis once every 24 hours. Earth has a natural satellite (the Moon) revolving around it.
Mars is the fourth planet from the Sun. It also known as the Red Planet because it surface is being covered with red dust. Mars is a cold and lifeless planet. One revolution of Mars around the Sun takes 687 days.
Jupiter is the largest planet in the Solar System. It is the fifth planet from the Sun. Most of Jupiter’s volume is made up of gases and ice with only a small rocky core. The atmosphere is composed of mainly hydrogen in gaseous and liquid forms together with helium, methane and ammonia. Jupiter has sixteen natural satellites or moons and takes about 12 years to revolve once around the Sun.
Saturn is the sixth planet from the Sun. It is surrounded of a system of rings which make it the most striking and beautiful planet when viewed through a telescope. Saturn is the second-largest planet in the solar system. However, it is lighter than a body of water of the same size. Saturn is thought to have a small, rocky high-temperature core surrounded by ice and ammonia, mixed with grit and gases.The time taken for Saturn to revolve around the Sun is around 29 years.
Uranus is the seventh planet from the Sun in the solar system. This planet is blue because it has cold gases, mainly made up of hydrogen and helium. Uranus also has a ring around it but the ring cannot be seen clearly because it is too thin and dim. It has five moons, and it rotates on its own axis slightly more slowly than Saturn. The time taken for Uranus to revolve around the Sun is around 84 years.
Neptune, the eighth planet from the Sun is almost the twin of Uranus. It is a little heavier than Uranus and is very slightly bigger. It is bluish-green.Neptune consists mainly of ice with some rocks and gases, and has less atmosphere. It has two moons and takes about 165 years to revolve once around the Sun.