The word ‘Solar’ comes from the Latin word ‘Sol’ which means Sun. Solar System, means the Sun, and the smaller bodies that move around it, which include the eight planets, their satellites, and thousands of asteroids, comets and meteors. The average distance of the Sun from the Earth is about 150 million km. The light of the Sun travelling at a speed of 3,00,000 km per second takes about 8 minutes and 20 seconds to reach the surface of the Earth. The temperature of the Sun at its surface has been calculated at about 6000oC and at its centre it is about 1.5 million degree Celsius. Planets are the heavenly bodies which do not have their own heat and light. These bodies reflect the light of the Sun and are called planets. Planets according to the distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter,Saturn,Vranus & Neptune. Mercury is the nearest planet to the Sun and Neptune is the farthest. This makes Mercury one of the hottest planers and Neptune the coldest. The Jupiter is the largest and Mercury is the smallest Planet. The Eight planets in order of their sizes are – Jupiter, Saturn m Uranus, Neptune, Earth, Venus, Mars and Mercury. Venus is known as the Morning and Evening Star. |
The Earth our home is the only planet in the Solar System where life is possible. This is due to its favourable temperature. It was first Aristotle and later Copernicus, who declared that Earth is a Sphere. Actually the Earth is not perfect Sphere. It bulges at the Equator and is flat at the Poles. Thus its Equatorial Diameter is more than its Polar Diameter. The Earth is often called Blue Planet, because of the presence of water.
Satellite: Satellite is the heavenly body in the Solar System which revolves around a planet. The Moon is the Satellite of the Earth. It was the only known Satellite A.D. 1610. Mercury and Venus are the only planets that do not have any known Satellites. The Average distance of the Moon from the Earth is about 3, 84,400 km and its mean diameter is about 3480 km. The Moon has no heat or light of its own. It reflects the light of the Sun. Sunlight reflected by the Moon reaches the Earth in about 1.35 seconds, seen from the Earth, the Sun and the Moon appear to be of the same size. The Moon also rotates on its axis. The time taken by the Moon to complete one rotation and one revolution is the same – 27 days and 8 hours. Yuri Gagarin was the first man in space. In April 1961, he orbited the Earth once. Neil Armstrong was the first man on the Moon, followed by Edwin Aldrin. They landed on the Moon on 21st July, 1969. Asteroids: Very small planet-like solid body found between the orbits of Mars and Jupiter. It is believed that Asteroids are pieces of some planet which probably exploded soon after its birth.
Comets: Sometimes balls with glowing tails shine in the sky, night after night. These luminous heavenly bodies are comets. Comets consist of ice, dust and frozen gases. Comets appear suddenly. The best known comet is Helley, which can be seen from the earth every 76 years. It was seen in 1986. Meteors: Meteors are the small particles coming from interplanetary space. They are heated by friction with atmosphere and become luminous. They are also called Shooting Stars. There are crores of stars with their families in space. About 10,000 crore stars make up the galaxy to which we belong called the Milky Way Galaxy or the Akash Ganga. Inside the Milky Way, the star nearest to the Sun is Proxima Centauri.It is more that 4.2 light years away. A Light Year is the distance travelled by light in one year. This unit is used to measure distances in space.
Important: The greatest depth in the oceans is at Mariana Trench on the Eastern Side of the Pacific Ocean. It is about 11,022 meters deep.
The temperature of the ocean water in general, decreases from the Equator about (27oC) to the Polar region (icy cold). The ocean water is always restless. It is in constant motion through currents, Tides and Waves. The regular movements of water from one part of the ocean to another are called ocean currents on the basis of temperature, currents are of two types . e.g. Warm Current & Cold Current. The rise and fall of sea water due to the gravitational pill of Moon and Sun are called Tides. When the rise and fall is more predominant than the actual forward motion of water, we call it waves. The water of the oceans is inter-connected. Thus the level of water in the oceans and seas is the same throughout. This is called the sea level.
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