Local Time (LT) and Time Zones, The Date Line and Universal Time (UT)
Local Time (LT) and Time Zones, The Date Line and Universal Time (UT)
Local Time (LT) and Time Zones
⇒ Two important concepts, related to latitude and (especially) longitude are Local Time (LT) and Universal Time (UT).
⇒ Longitudes are measured from zero to 180° east and 180° west (or -180°), and both 180-degree longitudes share the same line, in the middle of the Pacific Ocean.
⇒ As the Earth rotates around its axis, at any moment one line of longitude”the noon meridian” faces the Sun, and at that moment, it will be noon everywhere on it. After 24 hours the Earth has undergone a full rotation with respect to the Sun, and the same meridian again faces noon. Thus each hour the Earth rotates by 360/24 = 15 degrees.
The Date Line and Universal Time (UT)
⇒ Longitude determines only the hour of the day-not the date, which is determined separately. The international date line has been establishedmost of it following the 180th meridian-where by commonagreement, whenever we cross it the date advances one day (going west) or goes back one day (going east).
⇒ That line passes the Bering Strait between Alaska and Siberia, which thus have different dates, but for most of its course it runs in mid-ocean and does not inconvenience any local time keeping.
⇒ Astronomers, astronauts and people dealing with satellite data may need a time schedule which is the same everywhere, not tied to a locality or time zone. The Greenwich Mean Time, the astronomical time at Greenwich (averaged over the year) is generally used here. It is sometimes called Universal Time (UT).
⇒ The Royal Observatory at Greenwich in London was adopted as the site of the Universal Time meridian of longitude by the International Meridian Conference-a meeting of 25 nations in Washington DC on 22nd October 1884. The decision formalised the international standard time reference point of Greenwich Mean Time (GMT), which is still used to delineate world time zones.
Indian Standard Time (IST)
This is the imaginary line passing through mid of the standard Meridian in the middle of the country and standard time of the country is followed all over the country to avoid the inconvenience caused by the difference in local times of different places in the country. 8212°E or 82°30’E longitude, passing through Mirzapur (Amravati Chauraha) Uttar Pradesh, is the Standard Meridian of India. The time at this longitude is the standard time of India, called the Indian Standard Time (IST).
Lines crossing different countries
Tropic of Cancer Taiwan, China, Myanmar, Bangladesh, India, Oman, UAE, Saudi Arabia, Egypt, Libya, Niger, Algeria, Mali, Mauritania, South Sahara, Bahamas, Mexico
Tropic of Capricorn:Chile, Argentina, Paraguay, Brazil, Namibia, Botswana, South Africa, Mozambique, Madagascar, Australia, French Polynesia, Fiji, Tonga
Equator Ecuador, Columbia, Brazil, Sao Tome & Principe, Gabon, Congo, Democratic Republic of Congo, Uganda, Kenya, Somalia, Maldives, Indonesia, Kiribati
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