Universe is the vast empty space around us and everything that is in it. It contains numerous heavenly bodies like the sun, the planets, moon, stars , meteors and meteorites. Nobody knows the size of the universe. It is limitless.
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The three main constituents of the universe are:
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The solar system
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The stars
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The galaxies
The Solar System
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The solar system consists of the sun, the nine planets and their satellites, asteroids, comments and meteors.
The Sun:
The sun is at the centre of the solar system. It is a star. It is a hot, glowing sphere of gases. It emits light of its own.
The sun appears brighter and bigger than others stars because it is very close to the Earth. It is the nearest start which is visible during the daytime. It is at a distance of 150 million km from the Earth. It is stationary. It spears to rise in the east and set in the west. This is because the earth rotates on its axis from west to east.
The sun is about 5000 million years old and will continue to radiate light for the next 5000 years. It is a hot ball of gases-mainly helium and hydrogen. Surface temperature of sun is approximately 6000˚ C. The sun is approximately 100 times bigger than the Earth.
The Planets:
The heavenly bodies which revolve round the sun is fixed elliptical orbits are called planets. Each planet also rotates on its own axis.
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The word ‘planet’ comes from the Greek word meaning ‘wanderer’ The names of the nine planets of the solar system in increasing order of their distance from the sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Of these nine planets, Pluto is the smallest and Jupiter is the largest.
The period of rotation of the planet round its own axis from west to eat is called a planet day. For us, on earth, a planet day is of 24 hours. Jupiter has a planet day of only 9 hours and 55 minutes, while Venus has the longest planet day of 243 days.
Brightness and Colors of Planets:
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The planets do not have light of their own. They appear brighter when light from the sun falls on them. The surface of the planet reflects the sunlight due to which the planet shines.
Venus is the brightest planet. It is called morning start when it appears in the eastern sky before sunrise. It is called evening star when it appears in the western sky after sunset. Different planets are of different colors. Mars in the night sky appears reddish in colors. Hence, it is also refereed to as the red planet. Jupiter appears almost as bright as Venus in the night sky. Jupiter can be seen throughout the night. It is the largest planet of the solar system. Mercury can be observed just after sunset in the west or just before sunrise in the east. Saturn has several rings around it.
All the planets revolve around the sun in almost the same plane except Pluto which moves in a different plane.
Natural Satellites:
An object which revolves round a planet (as the moon revolves around the Earth) is called a satellite. The word comes from the Latin satellites, meaning ‘attendant’. All satellites move round their parent planets in paths called orbits. Seven out of the nine planets in the solar system have satellites or moons. The only two planets which do not have satellites or moon are Mercury and Venus. The earth has only one moon. The moon of the Earth completes one revolution around the Earth is 27.3 days. It also takes 27.3 days to complete on rotation on its axis. The moon is much smaller than the Earth.
Comets:
These are heavenly objects which revolve round the sun like planets but have a very long period of revolution. A comet has a distinct head and a glowing tail which is always directed away from the sun. It brightens as it approaches the sun. Once in many years one happens to see a comet with the naked eye.
Meteors and Meteorites:
Meteors are small heavenly object moving round the sun. Sometimes, they get displaced from their orbit, and enter the Earth’s atmosphere from outer space with a very high speed. Friction between these objects and atmospheric air causes the objects to get red hot and finally burn out. Meteors are seen as bright streaks of light in the sky. They are therefore called shooting stars.
Sometimes, meteors of greater size reach the Earth without getting burnt. Then these are called meteorites. Some of the meteorites can be seen in museums.
Asteroids:
Asteroids are small heavenly bodies that lie between the orbits of Mars and Jupiter. These are much smaller than a planet and orbit round the sun.
The Stars
A star is heavenly body which has heat and light of its own. It is a hot, glowing sphere of gases which emits light all the time. Each start is a sun. Stars are very big heavenly bodies. They are much larger than the Earth. Some stars are even large than sun. Stars appear smaller and dimmer because they are very far away from us than the sun. The sun appears much larger than other stars because it is the Earth’s nearest star.
Stars twinkle due to air currents in the atmosphere. The color of any star depends upon its temperature. They appear to be near each other, but actually they are apart by distances of billions of kilometers. These distances are measured in terms of a very big unit of distance called light year. Light is used to measure distances in the universe. One light year is the distance traveled by light in one year.
One light year = speed of light X one year
Speed of light = 3, 00,000 kilometer per second
Seconds per year = 3,15,36,000
One light year = 3,00,000 X 3,15,36,000 = 9,460,800,000,000 Kilometers
Thus, one light year is equal to 10 million million kilometers. Time taken by sunlight to reach the earth is 8.3 minutes. You may say that sun is about 8.3 light minutes away from the Earth.
Next to the sun, Proxima Centauri is the nearest star. It is about 4.3 light years away from the Earth. Its distance from the Earth is about 6 billion kilometers.
Galaxy
A galaxy is a larger cluster of stars. Each galaxy contains billions of stars held together by forces of gravitational attraction. Galaxies have different shapes and sizes. Our galaxy is called the Milky Way. This galaxy is spiral in shape and is wider at the center. It appears as a huge strip of faintly glowing light from north is south across the sky. The Milky Way is commonly called the Akashganga because it appears as a river of bright light flowing through the sky. The sun and about 20 billion stars are a part of this galaxy. There are around hundred billion galaxies in the universe. These galaxies are the building blocks of the universe as atoms are the building units of the all substances.
Constellations:
Groups of stars arranged in interesting patterns are called constellations. These patterns form outlines of imaginary figures of animals or human beings. All the constellations appear to revolve round the pole star which remains fixed. All the stars in the constellation stay together. Due to rotation of the Earth about its own axis from west to east, as seen looking down from above the Earth’s North Pole, these constellations appear to move in the sky from east to west.
Our ancestors have named some constellations after familiar objects which they seem to resemble. One of the most famous constellations is Ursa Major. It is called by different names such as Big Dipper, the Great Bear or the Saptarishi (seven stars).
The name ‘Big Dipper’ is derived from the word ‘dipper’ which means a large spoon. There are seven stars in this constellation – three stars in its handle and four in its bowl.
The Pole Star
This is a star which is seen directly above the North Pole on the axis of rotation of the Earth. It is called the North Star or Dhrav Tara. It remains stationary at the same place in the north. It is not too bright and has no other star around it. All constellations appear to revolve around the Pole Star. The Pole star lies on the imaginary line joining the two stars, at the end of Ursa Major in the North direction. In ancient times, the Pole Star was used for navigation by the sailors at sea.
Artificial Satellites
Artificial satellites are man-made vehicles launched by rockets into orbit around the Earth. Since the launch of the first artificial satellite ‘Sputnik-1’ by Soviet Union. Thousands of satellites have been launched by countries like USA, France, and Russia, Great Britain, Japan and India. All the artificial satellites have a finite life and will eventually burn like meteors. Artificial satellites have a number of uses/functions. They may be weather satellites, communication satellites, or those which provide information about Earth’s resources, etc. While the weather satellites help in forecasting weather conditions and provide warning of cyclones, communication satellites relay telephone and television signals, allowing live transmission of events from all parts of the world.
India too has joined the select band of countries which are capable of launching satellites. Her first satellite called Aryabhatta was launched into space on April 19, 1975. Some other artificial satellites launched by India are Bhaskara-I, Bhaskara-II, Rohini, APPLE, INSAT-IB, INSAT-ID, INSAT-2As, etc. INSAT stands for Indian National Satellite. METSAT, launched on 12th September 2002, is the first exclusive meteorological services being provided by the INSAT systems, used earlier.
These artificial satellites can be observed as bright stars, traveling across the sky either just after sunset of before sunrise.
First Indian in Space
It is a matter of great pride that India became the fourteenth nation in the world to send a man into space. On 2nd April, 1984 Squadron Leader Rakesh Sharma became India’s first man in space when he was launched abroad Soyuz T- 11 spaceship from the Baikonour Cosmodrome in Kazakhastan (USSR).