Indian Standard Time (IST) is the time observed in India. Its time offset is UTC+5:30 at all times of the year.
Indian Standard Time is calculated at the Allahabad observatory. Allahabad is 82.5 °E of the Prime Meridian and as a result the time difference between Greenwich and Allahabad is exactly 5 hours and 30 minutes.
The entire country shares the same time zone. As a result sunrise and sunset times are substantially different across the breadth of the country. Another temporal inconsistency occurs because parts of India lie east of Bangladesh which observes UTC+6 as the standard time. Thus, moving from, say, Assam to West Bengal (both in India) in the same direction implies moving clocks forward and backward by half an hour as one passes over Bangladesh.
India's time zones were established in 1884, when there were two standard time zones, Bombay Time and Calcutta Time. The IST came into effect in 1905. However, Bombay still persisted with its own time zone, 39 minutes behind IST, until 1955.
Currently India does not observe daylight saving time, though it was used during the Sino-Indian War (1962), the Indo-Pakistani War of 1965 and the Indo-Pakistani War of 1971.
The Eastern Time Zone of the Western Hemisphere falls mostly along the east coast of Northern America and the west coast of South America. Its time offset is UTC-5 during Standard time and UTC-4 during Daylight saving time.
The time observed in this zone in the US portion is called Eastern Standard Time (EST) when observing standard time; Eastern Daylight Time EDT) when observing daylight savings.
In the United States, the following states are part of the Eastern Time Zone: Connecticut, Delaware, Florida, Georgia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, and West Virginia.
Additionally, the eastern half of Kentucky, the eastern third of Tennessee, the majority of Florida, and all of Michigan except the four Upper Peninsula counties that border Wisconsin (Gogebic, Iron, Dickinson, Menominee), and most of Indiana (all except the Chicago and Evansville metro areas) are part of the Eastern Standard Time Zone. The parts of these states not in the Eastern Standard Time Zone are in the Central Standard Time Zone.
In Canada, most of the provinces of Quebec and Ontario, plus most of the Qikiqtaaluk Region of Nunavut belong to the Eastern Standard Time Zone. In Mexico, the eastern state of Quintana Roo also followed EST for a brief period in the 1990s.
Other parts of North America that keep time by subtracting five hours from UTC include Panama, Jamaica, Haiti, Cuba, the Bahamas, and much of the Caribbean. In South America this time zone is observed in Colombia, Ecuador (except Galápagos), Peru, and, in Brazil, the state of Acre and the southwestern region of the state of Amazonas.