Time Zones

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People east of you will see the Sun on their meridian before you see it on yours. Those in Denver, Colorado will see the Sun on their meridian about 52 minutes before people in Los Angeles will see the Sun on their meridian. Denver residents experience local noon about 52 minutes before those in Los Angeles. That is because Denver is at longitude 105° West longitude while Los Angeles is at 118° West longitude (or 13° difference). For each one degree difference in longitude a person is from you, the time interval between his local noon and yours will increase by 4 minutes.

It used to be that every town's clocks were set according to their local noon and this got very confusing for the railroad system so they got the nation to adopt a more sensible clock scheme called time zones. Each person within a time zone has the same clock time. Each time zone is 15 degrees wide, corresponding to 15 degrees × 4 minutes/degree = 60 minutes = 1 hour worth of time. Those in the next time zone east of you have clocks that are 1 hour ahead of yours. The Pacific timezone is centered on 120° W longitude, the Mountain timezone is centered on 105° W longitude, etc.

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last updated: May 12, 2010

Is this page a copy of Strobel's Astronomy Notes?

Author of original content: Nick Strobel