The Solar System

The solar system comprises the sun and its nine planets which are believed to have been developed from the condensation of gases and other lesser bodies. All the planets revolve round the sun in elliptical orbits. Like the earth, they shine only by the reflected light of the sun. The sun has a surface temperature of 6000'C and increases to 20 million'C in the interior. All over its surface are fiery gases that leap up in whirls of glowing flames like a volcano in eruption. In size, the sun is almost unimaginable. It is about 300,000 times as big as the earth! Amongst the nine planets, MERCURY is the smallest and closest to the sun, only 57,900,000 km away. It thus completes its orbit in a much shorter space of time than does earth. A year in Mercury is only 88 days. VENUS, twice the distance away from the sun, is the next closest planet. It is often considered as "Earth's twin" because of their close proximity in size, mass (weight) and density. But no other planet is in any way comparable to EARTH which has life and all the living things we see around us. Like many other planets, the earth has a natural satellite, the moon, 384,629 km away, that revolves eastward around the Earth once in every 27 days. The fourth planet from the sun is MARS which has dark patches on its surface and is believed by most professional astronomers to be the next planet after Earth to have the possibility of some plant life. Much attention has been focused on Mars to explore the possibilities of extending man's influence to it. Next comes JUPITER, the largest planet in the solar system. Its surface is made up of many gases like hydrogen, helium and methane. It is distinguished from other planets by its circular light and dark bands, and the twelve satellites that circle round it. As it is more than 780 million km from the sun, its surface is very cold, probably about - 128'C. Another unique planet is SATURN which has three rings and nine satellites around it. In size, it is the second largest after Jupiter. It is so far from the sun that it takes 29 and half years to complete its orbit. The seventh planet, URANUS, was not known to astronomers until the late eighteenth century when it was first seen as a faint bluish-green disc through a very powerful telescope. It is another giant planet, 50 times larger than earth and 15 times as heavy. Unlike other planets, Uranus orbits around the sun in a clockwise direction from east to west with five satellites revolving round it. The two outermost planets in the solar system, Neptune and Pluto, are just visible with telescopes. Their discoveries were the result of mathematical calculations on their irregular gravitational effects on neighbouring planetary bodies. NEPTUNE closely resembles Uranus, except that it has only two known satellites and is probably much colder. Pluto is smaller than earth. As the orbits of the planets are not circular but elliptical, the distance of Pluto from the sun during perihelion (i.e. when it is closest to the sun) is 4451 million km, and at aphelion (i.e. when it is farthest from the sun) is 7348 million km. A year in PLUTO is no less than 247 years on earth! Due to their very recent discovery and their extreme remoteness from the earth, very little is so far known about these last two planets.

Exploring the Universe

On a bright night when you look up at the sky, it seems to be studded with stars. Little do you realize that each of the stars is far bigger than the earth on which we live. Some of the larger ones have been estimated to be many millions of times the size of the earth. The stars are not scattered regularly in space; they occur in clusters, better described as galaxies or nebulas. Each galaxy may contain as many as 100,000 million stars. The stars appear small to us even through a telescope because they are so far away. The light from the nearest star traveling at the speed of light (i.e. 299,400 kilometres/186,000 miles per second) takes something like four years to reach us. A ray of light from the sun takes about eight minutes to reach the earth. Light takes only a second to reach us from the moon. In recent years much interest has been shown and vast expenditure has been made, particularly by the United States and the Soviet Union, in exploring outer space. Many problems have had to be overcome. For example, the problem of meeting man's basic needs of oxygen, water and food; temperature control and the problem of weightlessness, while he is in outer space. A number of technological advances have been made in the course of these space programmes, particularly in the fields of radio and television communications. On 4 October 1957 the Soviet Union successfully launched the first artificial satellite (Sputnik I). This was followed by a series of unmanned spacecraft that sent back to earth television pictures of the surface features of the heavenly bodies, and coded information by radio. In April 1961 the Soviet Union successfully placed the first man, Yuri Gagarin, in orbit round the earth. Since then there have been many manned flights into outer space, culminating in the first landing on the moon by American astronauts in a rocket called Apollo 11 in July 1969. The importance of space exploration to man in general, and to geographers and other earth scientists in particular, is immense. Much has been learnt about space temperature, the magnetic fields of the sun and the earth, the amount and kinds of radiation, the shape and extent of the earth's upper atmosphere. We have learnt much about the surface of the moon and about human adaptability to its environment.