## Earth Sciences and Ecology Question #370

david, a 14 year old male from the Internet asks on April 16, 1998,

Why are the time zones on maps rated as longitude & latitude in degrees and minutes?

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### John Digby Reid answered on April 16, 1998

Latitude and longitude are a system acceptedthe world over for specifying position on the nearly spherical planet we call Earth. Lines of latitude, which run east-west, give the location of a place north or south of the equator and range from 0 degrees at the equator to 90 degrees (North or South) at the poles. The equator, which divides the Earth into northern and southern hemispheres, is unique because it is the longest line of latitude. Latitude 90 degrees is a point at the pole.

Lines of longitude run north-south. Zero degrees (called the prime meridian) runs through Greenwich, outside London, UK, and increases to 180 degrees East as you go east, and to 180 degrees West as you go west. That makes 360 degrees of longitude all the way round. As it takes 24 hours for the earth to rotate once round, every 360/24 = 15 degrees of longitude is equivalent to a time difference of one hour. Time zones are established for geographical blocks of approximately 15 degrees of longitude, a suggestion first made by Canadian, Sir Stanford Fleming. The exact boundaries are set provincially and vary quite a bit to suit administrative convenience. They are usually a whole number of hours different from the time at Greenwich, but sometimes you find half hour differences (Newfoundland), and in parts of the world even quarter hour differences. The minute (from the Latin, minutus, meaning small) is a subdivision. For time, a minute is a one-sixtieth part of an hour. For latitude and longitude, a minute is a one-sixtieth part of a degree. For even greater precision, seconds are used as a sixtieth part of a minute. So, if the Titanic sank at 41 degrees, 46 minutes North latitude and 50 degrees, 14 minutes West longitude it means that it is 41 and 46/60 degrees north of the equator, and 50 and 14/60 degrees west of the prime meridian. Sometimes for convenience of calculation these are expressed in the decimal system as 41.76666.... degrees North, and 50.23333... degrees West.

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