Time Zones

Date: 05/09/2003 at 22:20:01
From: Naomi
Subject: Time Zones

How do time zones work?

Date: 05/09/2003 at 23:04:11
From: Doctor Ian
Subject: Re: Time Zones

Hi Naomi,

The basic idea is this: Suppose someone standing in New York City goes 
outside and waits for the sun to reach its highest elevation during a 
particular day. When it happens, he starts a stopwatch running. 

Now, suppose someone is 15 degrees longitude to the west of him,
waiting for the sun to reach its highest elevation on the same day. 
When it happens, he calls the first person on the phone and tells her 
to stop the stopwatch. What will the stopwatch read? 

It should read very close to 1 hour. That is, in 1 hour, the sun moves 
15 degrees across the sky. It moves 360 degrees in 24 hours.  

Now, suppose we said that noon for _everyone_ is when the sun is
highest as seen from New York City. That would mean that for some
people, 'noon' would occur before the sun comes up, or after it sets.
Can you see how that would make concepts like 'morning', 'afternoon',
and 'evening' less useful for communicating?  

To make it easy for people to map the same set of hours onto more or
less the same motion of the sun across _their_ sky, we let people in
successive 'time zones' experience noon an hour later as the sun moves
from east to west. So when it's noon in Los Angeles, it's already one
o'clock in Denver, and two o'clock in Chicago, and three o'clock in 
New York. And yet, in each place, 'noon' looks pretty much the same.  

Does that make sense? Is it what you wanted to know? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/