China's Time Zone

Date: 12/01/2000 at 16:24:10
From: Zach
Subject: Time zones

Do you know why the Commonwealth of Independent States covers 11 time 
zones and China covers 1? I wonder why.

Date: 12/01/2000 at 17:03:42
From: Doctor Rick
Subject: Re: Time zones

Hi, Zach.

This is not a mathematical question, but a political question. Each 
nation's government decides where the time-zone boundaries fall. I 
don't know what sort of international agency or treaty might be 
involved in these decisions.

You're right, the People's Republic of China has a single time zone. I 
see that on this time zone map, for instance:

  World Time Zone Map - U.S. Naval Observatory
  http://aa.usno.navy.mil/AA/faq/docs/world_tzones.html   

Evidently the government of China decided that it didn't want to deal 
with different time zones, and it was able to impose this decision on 
the people. (I can't say, though, whether this arrangement was already 
in place before the Communists took power about 50 years ago.)

Looking at the map, I see that China covers a longitude range of about 
60 degrees. A difference of 1 hour in time (one time zone, nominally) 
corresponds to 15 degrees of longitude, so China is about 4 time zones 
in width. If the time zone lines followed the lines of longitude, 
China would fall into 5 time zones. Instead they chose to have one.

The former Soviet Union covers a longitude range of about 165 degrees. 
It falls into 11 time zones naturally. The government moved the 
time-zone lines around quite a bit, but not enough to eliminate any.

Part of the reason that the former USSR covers 11 time zones is that 
it is so far north. It is not 11/4 times as wide as China; the time 
zones are narrower at latitudes closer to the poles. Still, the former 
USSR is a long way from east to west, more than in China.

You might think about what effect China's choice has on the people. If 
the sun reaches its highest point (astronomical noon) at 12:00 in 
Beijing, what is the time when the sun is highest in the westernmost 
parts of the country? 

The answer will seem a bit odd, but not as odd as what would have 
happened if the Soviet Union had made the same choice, to have a 
single time zone!

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