Notes
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Topics to be Learn :
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Standard Time :
World standard time : It is determined by the 0° meridian or Prime Meridian. Since this Prime Meridian passes through Greenwich, this time is also known as Greenwich Mean Time or GMT.
Standard time : The local time of a particular meridian which is considered as the time of the whole nation or region is known as a ‘standard time’.
Indian Standard Time : The local time at 82.5° E meridian that passes through almost from the centre of India is considered as Standard Time of India i.e. ‘Indian Standard Time’.
- There is a difference of 5 hours and 30 minutes between the GMT and the IST. Indian standard time is ahead of GMT. It is also mentioned as +5.30. As a result, when it is 9 a.m. at the Prime Meridian, it is 2:30 p.m. that is 14.30 hours in India.
Standard Time of Various Countries : A table showing the days and time of the welcome of New Year in different countries and cities according to the Indian Standard Time is given.
Solution to the confusion of days:
- Man had studied the natural phenomena like Rotation, Revolution and develop the chronometric system for his purpose.
- Earth completes one rotation in 24 hours.
- Earth rotates eastward. Therefore, the eastern part of the earth is always ahead of Western part.
- When it is exactly noon i.e.12 o’clock afternoon on Greenwich, the time is ahead by 2-2 hours at every 30° latitude to the east of Greenwich.
- Same time, it is 2-2 hours behind the Greenwich time at every 30° latitude to the West of Greenwich.As a result of this ahead or behind timing, when it is Sunday noon at Greenwich, Sunday is just beginning to the east of 180° meridian and it is the end of Sunday in the west of 180° Meridian.
- It creates a difference of almost a day or 24 hours between the timing in the East and West of 180° Meridian.
- International Date Line is decided to overcome this confusion of 24 hour difference.
International Date Line :
International Date Line is an imaginary line drawn to the opposite of Greenwich Prime Meridian, i.e. with reference to 180° Meridian.
The day and date is always ahead by one day in the west of International Date Line than the day and date running in the east of International Date Line.
Although the IDL is drawn with reference to 180° Meridian, International Date Line is not a straight line like 180° Meridian.
In order to pass IDL only on ocean areas, IDL is turned to the east or the west of 180°. Hence, IDL is not a straight line. In other words, IDL is drawn in such a way to avoid passing over the land.
Q. What difference does it make in a day and date if IDL is crossed.
Time to the east and west of 180° meridian shows the difference of 24 hours. IDL is therefore drawn to overcome this problem of 24 hours difference.
Significance and use of IDL :