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- 1 0 latitude = 111 km.
- Some important latitudes are-
- Tropic of cancer – 23½ 0 N.
- Tropic of Capricorn – 23½ 0 S.
- The Arctic Circle – 66½ 0 N.
- The Antarctic Circle – 66½ 0 S.
- In 1884, it has been decided that the zero meridian is one that passes through the royal astronomical observatory at Greenwich near London.
- 180 0 meridian (International Date Line) is exactly opposite to the prime meridian (such points are called antipodal points).
- 82.5 0 East meridian is the standard time meridian of our country, it is 5 hrs 30 min ahead of the Greenwich mean time (GMT) and is situated at Naini near Allahabad.
- The earth is divided into 24 longitudinal zones, each being 15 0 or 1 hrs apart in time or 1 0 in four minutes are called standard time zones.
- Russia has as many as 11 time zones.
- Both USA and Canada have five time zones viz. the Atlantic, eastern, central, mountain and pacific.
- International date line:- the 1800 meridian running over pacific ocean deviating at Fiji, Samoa and Gilbert islands. (deviates at land masses)
- While crossing date line from west to east – repeats a day.
- While crossing date line from east to west – losses a day.
- Generally a total of seven eclipses (including solar and lunar eclipse) take place in a year.
- Solar eclipse (moon comes between) –
- It can be partial or total.
- Happen only on a new moon day.
- But it doesn’t occur in every new moon day.
- Lunar eclipse (earth comes between) –
- Happens only on a full moon day.
- But not on every full moon day.
- Structure of earth’s interior –
- The crust.
- Thickness varies from 8 km to 40 km.
- The rocks are rich in lighter minerals like Si and Al.
- Layer is also called Sial.
- Average density = 2.7 gm/cm3.
- The mantle.
- About 2900 km in thickness.
- Minerals are in semi solid state.
- Upper mantle (Asthenosphere) is about 250 km thick.
- Layer is also called Sima.
- Average density = 5.68 gm/cm3.
- The core.
- Average density = 17.2 gm/cm3.
- Discontinuities: The various layers are separated by discontinuities, which are advent in seismic data.
- Composition of earth –
- Composition of earth’s crust –
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