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# Class 3: Shape and Motion of the Earth

### Topics Covered in this Lecture

1. Shape of the Earth
2. Latitudes and Longitudes
3. Various Motions of the Earth
4. Time and Date Lines

The imaginary lines drawn parallel to the equator at an equal distance away from each other are known as parallel of latitude.

Because they are on equal distance away from each latitude is use to calculate the distance, where 1-degree = 111 km

City = 20-degree latitude

=20x111km away from equator.

The most important latitudes are 0 degree latitude or equator.

23.5 N – tropic of cancer

23.5 S – tropic of Capricorn

• The apparent movement of the sun is only between the tropic of cancer or tropic of Capricorn. Sun’s rays are more or less vertical throughout the year over the equator.
• The sun rays is Vertical at least once in a year between 0-23.5 latitudes.

March – Kerala very hot

21st June – tropic of cancer

• The sun rays are never Verticle in the temperate and the frigid zones of the world.

• In the frigid zones the length of a day can be greater than 24 hours.

• As we move away from the equator the length of a day increases.

• Longitudes represent the angular distance from the east or the west of the prime meridian.

• As longitudes run from pole to pole, the distance between the two longitudes keeps on changing. It is maximum at the equator while 0 km near the poles.

• As they are not equidistance, they cannot be used for calculating the distance between the two places.

360- degree = 24 hours

1 degree       =  4 minutes

15 degree     =  4×15=60 degree = 1 hour

• Longitudes are used for calculation of time. in 1884, it was decided that the line which passes through Greenwich (London) would be taken as prime meridian or 0-degree longitude the time at this prime meridian is known as international standard time (IST)

OR

Universal standard time (UST)

• All the other meridians are drawn East or west of GMT

Thus if we go to the east of 0-degree longitude we gain time and thus we have to add the time and if we go to the west of this longitude, we have to lose the time or subtract.

### CONCEPT OF TIME ZONES

• The countries which are big in terms of east-west dimensions as the different longitudes pass through them. They have numerous time zones. Equator countries such as the USA, Russia, etc.

• India has decided to accept 82’30 longitude as its standard time which is 5.30hills ahead.

• But as per government policies some of the big countries such as India and china have only one time zone.

• India ideally should have two time  zones because the distance between eastern and western states of India in terms of longitudes is 30 degree that is India extends from 6817 degrees east to 97’25 east and therefore the difference of time between Gujarat and Arunachal Pradesh is 2 hours though India

• Officially follows only one time zone the industrial act allows some of the industries such as tea plantations to have their own time and thus we have chai Bagan time which is 1 hour ahead of Indian standard time.

### INTERNATIONAL DATE LINE

• It is a line at which there’s a change in date. A traveler going eastward when he reaches 180 degrees west, he is ahead of GMT by 12 hours. Similarly, the person going westwards is behind GMT by 12 hours at 180 degrees.

• But since this both the lines are the same, crossing one day and therefore this line is known as an international dateline.A person going eastwards if the international date line (IDL)

• The international date line I straight line and follows 0-degree longitude but IDL though starts from 180-degree longitude after passing through the Bering strait, it becomes zig-zag to avoid the confusion of dates in the smaller countries.