Lesson 2, Topic 2
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CHAPTER-2 Globe: Latitudes & Longitudes

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Earth is Not a Sphere

  • Our Earth is not a sphere it is slightly  flattened at poles.
  • A globe gives an idea about its look.
  • Without latitudes and longitudes it’s difficult to tell location on a globe.

Axis of Earth

  • Two points on the globe through which the needle passes are two poles – North Pole and South Pole.

  • The globe can be moved around this needle from west to east just as the earth moves.

Equator and Latitudes

Latitudes Indication

  • All parallels north of the equator are called ‘north latitudes.’ Similarly all parallels south of the equator are called ‘south latitudes.’

  • The value of each latitude is, therefore, followed by either the word north or south. Generally, this is indicated by the letter ‘N’ or ‘S’.

Important Parallels of Lattitudes

  • Besides the equator (0°), the North Pole (90°N) and the South Pole (90° S), there are four important parallels of latitudes.
  • Arctic Circle at 66½° N

  • Tropic of Cancer (23½° N)
  • Tropic of Capricorn (23½° S)
  • Antarctic Circle at 66½° S

Heat Zone of the Earth

  • Torrid Zone (Maximum Heat Zone)
  • Temperate Zone (Moderate Heat Zone)
  • Frigid Zone (Very Cold Zone)

What are Longitudes?

  • Longitude, is a geographic coordinate that specifies the east–west position of a point on the Earth’s surface, or the surface of a celestial body.

  • It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda.

  • They are semicircles and the distance between them decreases steadily polewards until it becomes zero at the poles, where all the meridians meet.

What is Prime Meridian?

  • A prime meridian is the  meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle.

  • In 1884, the International Meridian Conference established an internationally recognised single meridian.

  • It is also known as Greenwich Meridian because it passes through the place called Greenwich (where the British Royal Observatory is located) in London.

Longitude and Time

  • As the earth rotates from west to east hence those places which are east of Greenwich will be ahead of Greenwich time and those to the west will be behind it.

  • The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in four minutes. Thus, when it is 12 noon at Greenwich, the time at 15° east of Greenwich will be 15 × 4 = 60 minutes, i.e., 1 hour ahead of Greenwich time, which means 1 p.m.

  • But at 15° west of Greenwich, the time will be behind Greenwich time by one hour, i.e., it will be 11.00 a.m.

Longitude and Time

Why Do We have Standard Time?

  • For a country like India which is widely spread from 68°E to 97°E it is very necessary to have a standard time.

  • 82½° E (82° 30’E) is treated as the standard meridian. The local time at this meridian is taken as the standard time for the whole country. It is known as the Indian Standard Time (IST).

  • India located east of Greenwich at 82°30’E is 5 hours and 30 minutes ahead of GMT. So it will be 7:30 p.m. in India when it is 2:00 p.m. noon in London.

Exercise for You:

What is Prime Meridian?

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