World Geography

Longitude & Time
Some Facts About the Earth, the Sun, and Telling Time:

1. The Earth turns or rotates on its axis once every 24 hours.
2. The direction of the Earth's rotation is counterclockwise; that is, from west to east.
3. In a complete 24-hour rotation the Earth turns 360 degrees. Since there are 24 hours in a day that means that the Earth rotates 15 degrees every hour (360/24= 15 degrees). Each 15 degrees of longitude on a map stands for one hour of time.
4. The Prime Meridian, 0 degrees longitude, is the starting line for telling time on Earth. If it is 12:00 noon on the Prime Meridian, it will be 11:00 am on all the places on the 30 degree west line, and so on all the way to the 180 degree line of longitude.

Conversely, if it is 12:00 noon on the Prime Meridian, it will be 1:00 pm in all places on the 15 degree E line of longitude, and 2:00 pm in all places on the 30 degree E line, and so on to the 180 degree line of longitude.

1. The Earth turns a new "face" to the sun constantly; thus, a person standing on a given line of longitude experiences dawn, then day, then dusk, then night.
2. All of the above applies to solar time. In general, nations follow "sun time," but make time zones within their countries. In doing so, communities within a zone will all have the same time. As persons go from one zone to another they "lose" or "gain" an hour of time depending on whether they are traveling east or west.

Time zones sometimes have irregular dividing lines to avoid dividing communities or states. If this were not done one side of a street could have one time, the other side could have another.

1. Time zones are generally shown on Mercator-type maps where the lines of longitude are shown as parallel, thus making for easier reading.