Short Notes - Physical Geography
Category : UPSC
Physical Geography
Planet Earth
- The Earth is the fifth biggest planet in the solar system.
- The form of Earth is 'Oblate spheroid'.
- The axis of the earth is inclined to the plane of Earth's orbit at an angle of 66 l/2°giving rise to different seasons and varying lengths of day and night.
- At equator, day and night are of equal length throughout the year.
- The Mid-day Sun shines vertically overhead at least once a year between the Tropic of Cancer and the Tropic of Capricorn. Thus, this region receiving the maximum heat is called Torrid Zone.
- Temperate Zones are the areas where climatic condition is not extreme. The area lies between the tropics and polar region C231/20 x 66V20) having moderate climate.
- Frigid Zones: These are the two extremely cold zones situated in the Polar Regions extending to the Arctic circle in the North and to the Antarctic circle in the South.
- Equinox: It is a day of the year when the duration of day and night is equal and the position of the Sun is in its zenith. In a year there are two equinoxes. September Equinox, i.e.
- September 23rd, and March Equinox (March 21st).
- Solstice: Like equinoxes there are two solstices also, June 21st and December 21st . This is the time when Sun reaches either its highest or lowest point at noon resulting into shortest and longest day of the year in a hemisphere.
- Earth rotates on its own axis from west to east once in every 24 hours causing day and night.
- It revolves round the Sun in an orbit once in every 365 1/4 days causing the seasons of the year.
Latitudes and Longitudes
- Latitude is the angular distance of a point on the Earth's surface measured in degrees from the centre of the Earth.
- Longitude is the angular distance, measured in degrees along the equator, east or west of Prime Meridian (Prime Meridian that passes through Greenwich near London). It is also considered as 0°
- Equator, i.e. 0° is the biggest latitude that divides Earth into two equal hemispheres (North and South).
- Tropic of Cancer is 23.5° N
- Tropic of Capricorn is 23.5° S
- Arctic Circle is 66.5° N
- Antarctic Circle is 66.5° S
- This is the Prime Meridian from which all other meridians radiate eastwards and westwards up to 180°.
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Latitudes
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Major Continents
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Major Countries
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Tropic of Cancer
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North America, Africa and Asia
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Bahamas, Mexico, Mauritania, Mali, Western Sahara, Algeria, Niger, Libya, Egypt, Saudi Arabia, India, China, Abudhabi, Oman, Bangladesh, Burma, and Taiwan.
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Equator
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South America, Africa, Asia
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Equador, Colombia Brazil, Sao Tome & Prince, Gobon Republic of Congo Democratic Republic of Congo, Uganda, Kenya, Somalia, Maldives, Indonesia.
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Tropics of Capricorn
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South America, Africa, Asia
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Chile, Argentina, Paraguay, Brazil, Namibia, Botswana, South Africa, Mozambique, Madagascar, Australia, French Polinesia, Caledonia, Fiji, Tonga and Coolis Island, etc.
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Standard Time and Time Zones
- The whole world has been divided into 24 standard time zones.
- Each zone is separated by 15° longitudes or by 1 hour or by 1° for 4 minutes.
- In India, the longitude of 82° 30° E, passing through the area near Allahabad is considered as the Standard Meridian. This is known as Indian Standard Time (1ST). 1ST is 5 hours 30 minutes ahead of GMT. Tropic of Cancer passes through 8 states of India: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, West Bengal, Tripura and Mizoram.
International Date Line
- A traveller going eastward gains time from Greenwich where he will be 12 hours ahead of GMT.
- Similarly, going westwards, he loses 12 hours till he reaches 180° W.
The Earth's position with respect to the Moon
- Apogee: Period of the farthest distance between the Moon and the Earth (407,000 km).
- Perigee: Period of nearest distance between the Moon and the Earth [356,000km).
Earth's position with respect to Sun
- Perihelion: Period of the nearest distance between Earth and the Sun (a 147 million km). The date of perihelion varies between 3rd to 5th Jan.
- Apehelion: Period of the farthest distance between the Earth and the Sun (appr. 152 km). The date of Apehelion varies between 4th to 6th
July.
Lithosphere (Earth's Interior)
- The Crust is the outer most part of the Earth which is solid, cool and brittle. The thickness of the Earth's crust varies between 8 and 60 km which is divided into two parts: upper crust and lowe crust. The density of crust varies between 2.8 to 3.0 g/cm3. The temperature of crust varies between 200°C to 400°C from top to bottom.
- The Mantle -The mantle extends from 60 km to 2900 km of depth.
- The Core- Inner solid core also known as Barysphere having temperature up to 6000°C, goes up to a depth of 6371 km at the centre of the Earth. The average density of core ranges between 13.3 to 13.6 g/cm3.
