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Time zone

A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.

This article is about time zones in general. For a list of time zones by country, see List of time zones by country. For more time zone lists, see Lists of time zones. For other uses, see Time zone (disambiguation).

Each time zone is defined by a standard offset from Coordinated Universal Time (UTC). The offsets range from UTC−12:00 to UTC+14:00, and are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes, such as in India and Nepal. Some areas in a time zone may use a different offset for part of the year, typically one hour ahead during spring and summer, a practice known as daylight saving time (DST).

Time in outer space

Orbiting spacecraft may experience many sunrises and sunsets, or none, in a 24-hour period. Therefore, it is not possible to calibrate the time with respect to the Sun and still respect a 24-hour sleep/wake cycle. A common practice for space exploration is to use the Earth-based time of the launch site or mission control, synchronizing the sleeping cycles of the crew and controllers. The International Space Station normally uses Greenwich Mean Time (GMT).[60][61]


Timekeeping on Mars can be more complex, since the planet has a solar day of approximately 24 hours and 40 minutes, known as a sol. Earth controllers for some Mars missions have synchronized their sleep/wake cycles with the Martian day, because solar-powered rover activity on the surface was tied to periods of light and dark.[62]

Daylight saving time

ISO 8601

Jet lag

Lists of time zones

Metric time

Time by country

Time in Europe

Time zone abolition

World clock

International Date Line

Asimov, Isaac (1964). "Abbe, Cleveland". Asimov's Biographical Encyclopedia of Science and Technology: The Living Stories of More than 1000 Great Scientists from the Age of Greece to the Space Age. Garden City, NY: Doubleday & Company, Inc. pp. 343–344.  64016199.

LCCN

Debus, Allen G., ed. (1968). . World Who's Who in Science: A Biographical Dictionary of Notable Scientists from Antiquity to the Present (1st ed.). Chicago, IL: A. N. Marquis Company. ISBN 0-8379-1001-3. LCCN 68056149.

"Abbe, Cleveland"

Biswas, Soutik (February 12, 2019). . BBC News. Retrieved February 12, 2019.

"How India's single time zone is hurting its people"

Maulik Jagnani, economist at (January 15, 2019). "PoorSleep: Sunset Time and Human Capital Production" (Job Market Paper). Retrieved February 12, 2019.

Cornell University

(Video). BBC News. August 14, 2015. Retrieved February 12, 2019.

"Time Bandits: The countries rebelling against GMT"

. BBC News. August 7, 2015. Retrieved February 12, 2019.

"How time zones confused the world"

Lane, Megan (May 10, 2011). . BBC News. Retrieved February 12, 2019.

"How does a country change its time zone?"

(Video). BBC News. March 24, 2011. Retrieved February 12, 2019.

"A brief history of time zones"

. doi:10.17487/RFC8536. RFC 8536.

The Time Zone Information Format (TZif)

Media related to Time zones at Wikimedia Commons