New words:
Purposes
propósitos boundaries fronteras offset compensación
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.
Each time zone is defined by a standard offset from Coordinated
Universal Time (UTC).
Some examples of time zones are:
UTC+0 United Kingdom, Portugal, the Canary Islands
UTC +1 central Europe Spain, France, Germany, Italy
UTC +2 Greece, Romania
The United States use 6 different time zones. The most well known
are:
Chicago UTC-6 (Central Standard time)
New York UTC-5 (Easter Standard Time)
Los Angeles UTC-8 (Pacific Standard Time)
Conversion between time zones obeys the relationship
- "time in zone A" − "UTC
offset for zone A" = "time in zone B" − "UTC
offset for zone B",
in which each side of the equation is equivalent to UTC.
The conversion equation can be rearranged to
- "time in zone B" = "time
in zone A" − "UTC offset for zone A" + "UTC
offset for zone B".
For example, the New York Stock Exchange opens at 09:30 (EST, UTC
offset= −05:00). In California (PST, UTC offset= −08:00) and
India (IST, UTC offset= +05:30), the New York Stock Exchange opens at
- time in California = 09:30 − (−05:00) + (−08:00) = 06:30;
-
- The time differences may also result in different dates. For example,
when it is 22:00 on Monday in Egypt (UTC+02:00), it is 01:00 on
Tuesday in Pakistan (UTC+05:00).
Daylight saving time
Many countries, and sometimes just certain regions of countries,
adopt daylight saving time (DST), also known as summer time, during
part of the year. This typically involves advancing clocks by an hour
near the start of spring and adjusting back in autumn ("spring
forward", "fall back"). Modern DST was first proposed
in 1907 and was in widespread use in 1916 as a wartime measure aimed
at conserving coal. Despite controversy, many countries have used it
off and on since then; details vary by location and change
occasionally. Countries around the equator usually do not observe
daylight saving time, since the seasonal difference in sunlight there
is minimal.