![]() Therefore, the maximum possible difference between times on Earth is 26 hours. You can see that the most extreme time zones are 14 hours at Line Islands (Kiribati), and -12 hours in and around Baker Islands (US). That way the current designation of time zones was established and is neatly summarized in this figure from Wikipedia commons. However, this time zone lines crossed political borders, so they were adapted and bent so that whole countries or at lest states remained within a single time zone. In other words, the moment the Sun reaches its maximum elevation in the sky won't be more than 30 minutes off from clock's noon. In principle they created time zones every 15°, so that no point would be more than 30 minutes off their solar time. For example: If you are in Eastern Island at longitude 109°W, it means your local time will be the time at Greenwich (know as Universal Time or UT) minus 7 hours 16 minutes ( $109/15=7.26\, h = 7h\, 16m$), if you use that time, the Sun will effectively be at its highest point at 12:00 h.īut as you can see, if you move in the east-west direction, every point would have a different time if we just use the above rule, which is very inconvenient, as the time in the east side of a city would be different than the time on the west side.įor this reason they invented Time Zones: to keep the same time within reasonable large areas. So if you know the longitude of a place, you just divide that longitude by 15 and you know how many hours you have to add/subtract from Greenwich reference time to get your local time. And due to the extent of the British Empire, in history was the observatory at Greenwich the one that stayed as the global reference point for time and longitude (because at first the main utility of precise time was to compute precise longitudes).Īs Earth's rotates 360° in 24 hours, that's 15° per hours. Therefore, time was kept by astronomical observatories. ![]() In principle the idea is that time anywhere should be such that noon happens when the Sun reaches its maximum elevation over the horizon. Time zones are defined by by man just to facilitate time keeping. If you are impatient, you can jump forward for the answer in bold font after the figure, and come back here for the explanation. The original wording of your question revealed that you are missing something about what time zones are, and how they are defined. ![]()
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