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
  • Equator, i.e. 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°.

 

 

      Latitudes

Major Continents

Major Countries

Tropic of Cancer

North America, Africa and Asia

Bahamas, Mexico, Mauritania, Mali, Western Sahara, Algeria, Niger, Libya, Egypt, Saudi Arabia, India, China, Abudhabi, Oman, Bangladesh, Burma, and Taiwan.

Equator

South America, Africa, Asia

Equador, Colombia Brazil, Sao Tome & Prince, Gobon Republic of Congo Democratic Republic of Congo, Uganda, Kenya, Somalia, Maldives, Indonesia.

Tropics of Capricorn

South America, Africa, Asia

Chile, Argentina, Paraguay, Brazil, Namibia, Botswana, South Africa, Mozambique, Madagascar, Australia, French Polinesia, Caledonia, Fiji, Tonga and Coolis Island, etc.

 

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.



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