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Geography - World & Indian (Earth - A quick look)

Written By STPORTAL on Sunday, March 18, 2012 | 2:57 PM

Geography - World & Indian (Earth - A quick look):

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Latitude, usually denoted symbolically the Greek letter phi, gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement in degrees (marked with °) ranging from 0° at the Equator to 90° at the poles (90° N for the North Pole or 90° S for the South Pole).

All locations of a given latitude are collectively referred to as a circle of latitude or line of latitude or parallel, because they are coplanar, and all such planes are parallel to the Equator. Lines of latitude other than the Equator are approximately small circles on the surface of the Earth;

Four lines of latitude are named because of the role they play in the geometrical relationship with the Earth and the Sun:

  • Arctic Circle — 66° 33′ 39″ N
  • Tropic of Cancer — 23° 26′ 22″ N
  • Tropic of Capricorn — 23° 26′ 22″ S
  • Antarctic Circle — 66° 33′ 39″ S

Only at latitudes between the Tropics is it possible for the sun to be at the zenith. Only north of the Arctic Circle or south of the Antarctic Circle is the midnight sun possible.

The reason that these lines have the values that they do lies in the axial tilt of the Earth with respect to the sun, which is 23° 26′ 22″.

As opposed to a degree of latitude, which always corresponds to exactly sixty nautical miles or about 111 km (69 statute miles, each of 5280 feet), a degree of longitude corresponds to a distance that varies from 0 to 111 km: it is 111 km times the cosine of the latitude, when the distance is laid out on a circle of constant latitude;

Longitude, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. In 1884, the International Meridian Conference adopted the Greenwich meridian as the universal prime meridian or zero point of longitude.

Each degree of longitude is further sub-divided into 60 minutes, each of which divided into 60 seconds. A longitude is thus specified as 23° 27′ 30" E.

Longitude at a point may be determined by calculating the time difference between that at its location and Coordinated Universal Time (UTC). Since there are 24 hours in a day and 360 degrees in a circle, the sun moves across the sky at a rate of 15 degrees per hour (360°/24 hours = 15° per hour). So if the time zone a person is in is three hours ahead of UTC then that person is near 45° longitude (3 hours × 15° per hour = 45°).

The International Date Line
The International Date Line (IDL), also known as just the Date Line, is an imaginary line on the surface of the Earth opposite the Prime Meridian which offsets the date as one travels east or west across it. Roughly along 180° longitude, with diversions to pass around some territories and island groups, it corresponds to the time zone boundary separating +12 and -12 hours GMT (UT1). Crossing the IDL travelling east results in a day or 24 hours being subtracted, and crossing west results in a day being added.
In the north, the date line swings to the east through Bering Strait and then west past the Aleutian Islands in order to keep Alaska (part of the United States) and Russia on opposite sides of the line and their territories due north and south of each other in concert with the date of the rest of each respective country.

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