Longtitude and time calculations

Different Time Zones

• A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes.
• Time zones tend to follow the boundaries of countries and their subdivisions because it is convenient for areas in close commercial or other communication to keep the same time. One way used to calculate local time is to use World Time Zones.
• This is a way to count how many hours ahead or behind a location is from you.
• The twenty-four hour time zones correspond to meridians of longitude. The Earth rotates around at 360°. That gives us day and night which is 24 hours long.
• Now to get the zones we divide, 360/24 = 15°. Hence, every 15° represents 1 hour and every 1° represents 4 minutes.
• Specifically, the zones are spaced 15 degrees apart, and each time zone differs from its adjacent time zone by one hour (earlier or later).
• That way, the times in each zone align with the local solar times of sunrise and sunset.

If time at 0° is 3 pm. Every 15° when moving eastwards time will increase by 1hour and decrease by 1hour every 15° when moving westwards. For example, there are 2 hours between 0° and 30° W, therefore the time at 30°W is 1pm.

Steps used in calculating the number of hours between two lines of longitude

1. First determine the number of degrees between the two places. For example, between 0° and 60°. So 60 – 0 = 60°.
2. Divide the number of degrees by 15° to determine the number of hours ° = 4 hours.
3. Then add the hours if you are moving to eastwards or subtract the hours if westward.
4. If when you divide you have a remainder, multiply the remainder by 4 to convert into minutes.

• For example, you want to know the number of hours between 0° and 35°E, first calculate the number of degrees between the two lines (35 – 0 = 35°), then divide by 15°. This gives 2 hours remainder 5. Then multiply 5 x 4mins = 20 mins.
• Therefore the number of hours between 0° and 35°E is 2 hours and 20 minutes.

Greenwich Mean Time (GMT) is often interchanged or confused with Coordinated Universal Time (UTC). But GMT is a time zone and UTC is a time standard. The Royal Observatory in Greenwich, London, United Kingdom. UTC is not a time zone, but a time standard that is the basis for civil time and time zones worldwide.

Note: There is no time difference between Coordinated Universal Time and Greenwich Mean Time.07:16 Friday, Coordinated Universal Time (UTC) is 07:16 Friday, Greenwich Mean Time (GMT)

• But using the time zones can be confusing for several reasons. First, some countries have several different time zones, and those local zones don’t always align perfectly with specific longitude lines.
• For example, prior to 1995, International Date Line split the country of Kiribati. The result was that the eastern part of Kiribati was a whole day and two hours behind the western part of the country where its capital is located.
• In 1995 Kiribati decided to move the International Date Line far to the east- which placed the entire country into the same day.
• The International Date Line (IDL) passes through the Pacific Ocean. It is an imaginary line, like longitudes and latitudes.
• The time difference on either side of this line is 24 hours. So, the date changes as soon as one crosses this line.
• To avoid any confusion of date, this line is drawn through where the sea lies and not land. Hence, the IDL is drawn in a zig-zag manner.
• Since the International Date line is completely political. It was set for the convenience for the nation states it passes around, hence the crookedness.
• It roughly follows the 180 degree longitude line. That line is opposite the politically set 0 degree longitude or prime meridian in Greenwich, UK.
• Also, remember that with 24 time zones the local time at another location can be anywhere from 0 to 24 hours different from you, and it can even be a different date!

 To access more topics go to the O Level Geography Notes page