prime Meridian & International Date Line

Prime Meridian and International Date Line 

* To determine time date and located places on earth we have to draw some Imaginary line like Longitude, Latitude, Equator, Prime Meridian for navigation and geographical information 

* In geography, latitudes and longitude are imaginary lines used to determine the location of the place on earth 

* Latitude is a geographic coordinates that specifics the north- south position of a point on the earths surface.

* Longitude is a geographic coordinate that specifies the east - west position of a point on the earth surface.

 

Equator Divides Earth into Northern and Southern Hemisphere -

Latitude 

* These are also called parallels, not equal 

* Among them the important ones are -

- Equator (0°),

- Tropic of Cancer (23 ½° N)

- Tropic of Capricorn (23½°S)

- Tropic of Cancer (23½°N)

- Tropic of Capricorn (66½° N)

- The North Pole (90°N)

- The South Pole (90°S)

- Arctic Circle (66½° N)

- Antarctic Circle (66 ½° S)

* They run in west to east direction 

* Total 181 latitude on the earth 

Longitude 

*: They are equal in length not parallel 

* These are also called as Meridian 

* They run in North South direction 

* There are total 360 longitudes

* They from great half circles.

* They cross the equator at right angles

*0° longitude is called the Prime or First Meridan 

* Opposite to 0° there is 180° longitude, which is called the International Date Line.

Facts and Bites-

* The Prime Meridian and the International Date Line are opposite to each other. These lines have Antipodal points.

- Antipodal points: points on Earths surface which are diametrically opposite, A pair of points antipodal to each other are situated such that a straight line connecting the 2 would pass through earth's center

- Prime Meridian passes through Royal Astronomical observatory at Greenwich near London. It determines  local time in relation to GMT or Greenwich Mean Time, which is sometimes referred to as world Time. New name UTC. ( Universal Time Coordinated)

- International Date Line passes through Pacific Ocean it determine date change.

Prime Meridian and Time -

* Earth makes one complete revolution of 360° in  one day or 24 hours.

  Therefore, in 1 hour it revolves (360/24) = 15° and as it passes through 15° in 1 hour or 60 minutes. It will pass through 1° (60/15) = 4 minutes 

* The earth rotates from west to east.

* So, every 15° we go eastwards , local time is advanced by 1 hour.

* Conversely, if we go 15° westwards. Local time is retraded by 1 hour.

* We may this conclude that places east of Greenwich see the sun earlier and gain  time, whereas places west of Greenwich see the Sun later and lost time.

Time zones -

Most of the countries of the world are sufficiently small in their east- west direction so as to lie totally within a single time zone.

* However, large countries may encompass several zones:

- Russia has 11 time zones 

- US has 6 time zones 

- Canada 6 and Australia 3 etc.

India Standard Line-

*In India we find a difference of about 1 hour and 45 minutes in the local times of Dwarka in Gujarat and Dibrugarh in Assam. Hence it is necessary to adopt the local time of some central meridan of a country as the standard time for the country.

* The longitude of 82½° E (82° 30'E) is considered as the Standard Meridan. The local time stated or mentioned at this meridian is considered as the standard time for the whole country. This is called as Indian Standard  Time ( IST)

* The Standard Meridian of India having the longitude 82°30' E, passes through Mirzapur in Uttar Pradesh 

International Date Line -

* The International Data Line is in the middle of the time zone defined by the 180° Meridan consequently, there is no time change when crossing the International Data Line - only the calendar changes, not the clock.

* When you cross the International Date Line going from west to east, it becomes 1 day earlier (January 2 to January 1)

* When you move across the line from east to west, it becomes 1 day later ( January 1 to January 2)

* Travelers crossing International Date Line from west to east ( from Japan to USA) repeat a day & travelers crossing it from east to west (from USA to Japan) lose a day

 The International Date Line is not Straight Line but why?

* International Date Line marks the place where each day officially begins.

* The International Date Line deviates from the 180th Meridan in the Bering Sea to include all of the Aleution  Island of Alaska within the same day and again in sourth Pacific to keep Islands of the same group within the same day

* International Date Line which is drawn at 180 degree longitude is not Straight but Zig-Zag line 

* The IDL doesn't cross nations , it passes around the for east of Russia and other archipelagos in the Pacific .

* In the north the date line turns to the east through the Bering Strait to avoid diving Siberia and then west.

* This is because if it is a straight line then it demarcates the same land mass into two parts and then both places have different dates on the same day. It would be very inconvenient if one part of a country had one date of the week while another part would have the different date.

* The date line passes equidistantly between the 2 Diomede Islands - Little Diomede Islands (US) and Big Diomede Islands ( Russian) - at a' distance of 1.5-2 km from each Island.

* The date line circumvents the territory of Kiribati by swinging far to the east, almost reaching the 150° Meridian 

* In the South Pacific the date line swings east such that few group of Islands have same date as New Zealand.