The earth is an oblate spheroid and not a true sphere because it is flattened at the poles and bulges out at the equator. Its circumference is 25,000 miles.Earth in Motion
The axis of the earth is the imaginary line on which the earth rotates.
Poles
They are the end of the axis. One end is called the North Pole and other the South Pole.
The Solar System
It is the name given to the group of nine major planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto) and their satellites, asteroids and hundreds of meteorites which revolve around the sun. They are kept in position on account of the pull of the sun on the planets. The Solar System originated from the huge gaseous mass called Nebulae.
The six most abundant elements in the earth’s crust are:(1)Oxygen 49.85% (2)Silicon 26.03% (3)Aluminium 7.28% (4)Iron 4.12% (5)Calcium 3.18% (6)Sodium 2.33%.
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Motion of the Earth
Rotation of the Earth
It turns round its own axis once in 24 hours,from West to East.
Revolution of the Earth
It revolves around the sun in about 365 days.
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The Boundaries of the Zones
The Torrid Zone
It lies between the Tropic of Cancer and Tropic of Capricorn,i.e 23 and a half degree North and South on either of Equator side.
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The Frigid Zone
The coldest zone which the sun’s rays are excluded entirely at least for one whole day in a year.
The Temperate Zone
It is between the Torrid and Frigid Zone 66 and a half degree North and South on either side of the Equator.
Latitude and Longitude
Lines of Latitude and Longitude are drawn on a map to locate the position of the place on the surface of the earth.
The equator is an imaginary circle on the surface of the earth, midway between poles. Latitude is the angular distance measuring North to South of the Equator from the plane of the Equator.
Meridian
Meridian means “Midway Line”. It is the imaginary line joining North and South Poles that, when any place comes directly below the sun, has its midday everywhere on it.
Prime Meridian
It is the meridian, that passes through Greenwich, that is placed near London.It is the zero degree longitude.
Local Time
Local Time or Sun Time of the place is the time which is reckoned according to the time when the sun’s altitude is the highest at that place. At this time, the shadow of a vertical rod fixed in the ground is the shortest.
Standard Time
If every place were to use its own local time that Standard Time of India is the local time of a place near Allahabad situated at 82 and a half degree E longitude.
Delta
It is a triangular-shaped land between the distributaries of a river.
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Tide
Tide is the periodic rise and fall of sea water twice in about 25 hours.
Causes of Tide
Two forces are acting on the earth:(a) the moon’s attraction, (b) the centrifugal force. Although these two forces are equal and opposite to each other at the centre of the earth yet that is not the case everywhere on the earth. Tide is caused by the difference in these two forces.
Types of Tides
Spring Tide, Neap Tide, Eclipses, Lunar Eclipses, Solar Eclipse, Currents, Contours.
Natural Regions
The Hot Belt, Savanna or Sudan Type, Desert Type, The Monsoon Type, The Mediterranean Type, Steppe Type, China Type, British Type, Siberian Type, EasternType, Tundra Type.
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