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Answers to Frequently Asked Questions
What is Latitude?
Any location on Earth is described by two numbers--its latitude and its longitude.
Actually, these are two angles, measured in degrees, "minutes of arc" and "seconds of arc."
These are denoted by the symbols (°,',") e.g. 35° 43' 9" means an angle of 35 degrees, 43 minutes and 9 seconds.
A degree contains 60 minutes of arc and a minute contains 60 seconds of arc--and you may omit the words "of arc"
where the context makes it absolutely clear that these are not units of time.
Calculations often represent angles by small letters of the Greek alphabet,
and that way latitude will be represented by l (lambda, Greek L), and longitude by f (phi, Greek F).
Here is how they are defined. For more details visit:Latitude and Longitude
Example:
Latitude (l) of Makkah is: 21° 27' N
Longitude (f) of Makkah is: 39° 49' E
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What is Local Time (LT) and Time Zones?
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.
When at your location the time is 12 noon, 15° to the east the time is 1 p.m., for that is the meridian
which faced the Sun an hour ago. On the other hand, 15° to the west the time is 11 a.m.,
for in an hour's time, that meridian will face the Sun and experience noon.
All countries of the world have their own time zones; only Saudi Arabia uses local times,
because of religious considerations.
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What is the Universal Time (UT) or (GMT)?
Suppose it is noon where you are and you proceed west--and suppose you could travel instantly to wherever you wanted.
Fifteen degrees to the west the time is 11 a.m., 30 degrees to the west, 10 a.m., 45 degrees--9 a.m.
and so on. Keeping this up, 180 degrees away one should reach midnight, and still further west,
it is the previous day. This way, by the time we have covered 360 degrees and have come back
to where we are, the time should be noon again--yesterday noon.
Hey--wait a minute! You cannot travel from today to the same time yesterday!
We got into trouble because longitude determines only the hour of the day--not the date,
which is determined separately. To avoid the sort of problem encountered above, the international date
line has been established--most of it following the 180th meridian--where by common agreement,
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).
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What is the Daylight Saving Time?
Daylight Saving Time is also called "summer time". It is a method of advancing clocks in
a global manner, in order to artificially expand the daylight hours. Clocks are set forward one hour
for most of the United States at 2 a.m. on the first Sunday of April.
Time reverts to standard time at 2 a.m. on the last Sunday of October.
In the European Union, it starts at 1 am the last Sunday in March, and ends the last Sunday in October.
During DST, clocks are turned forward an hour, effectively moving an hour of daylight from the morning to the evening.
For more details, visit: Daylight Saving Time over the world
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