Is there an easy way to understand how time zones work?

There are 24 different time zones -- but why do we have them? In this podcast, Marshall recounts how society evolved time zones, and also gives you an easy way to model the structure of time zones across the globe.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from house stuff works dot com
where smart happens. Hi Am Marshall Brain with today's question,
is there an easy way to understand how time zones work?
In January, people have a special interest in time zones.

(00:24):
That's because the shouting of Happy New Year happens at
midnight in your local time zone. Meanwhile, other time zones
either have already celebrated the new year or they're sitting
around waiting to do it. So cities in New Zealand
celebrate New Year's Day first, followed by cities in Japan, Australia, Russia, China,

(00:46):
and India, followed by cities in Europe and Africa, followed
by cities in North and South America, and then ending
on islands out in the Pacific Ocean like Hawaii and
finally Samoa. There are four separate time zones, so there
are twenty four separate times when balls drop, Happy New Year,

(01:06):
gets shouted, and people engage in flagrant public displays of
affection and intoxication. So let's start at the beginning. Why
do we have time zones? Keep in mind that there's
another way we could do this. We could have a
single time that holds true all over the planet. When
it's noon in Moscow, it could also be noon in London,

(01:27):
New York, and Los Angeles. The problem is that people
really don't like that. People much prefer for it to
be noon when the sun reaches its peak in the sky.
In order for it to be noon when the sun
reaches its peak, everybody needs to set their time according
to the sun. And this is how things used to be.
It used to be that there were no clocks. People

(01:49):
use things like sun dials. Then there were clocks, but
only the rich people could afford them because they were
really expensive. So a town would have a central clock
tower with bells loud enough to be heard all over town,
and the clock keeper would set the clock according to
the sun. This system worked well until trains started to
move quickly from town to town. In order to run

(02:12):
a punctual train schedule, all the towns needed to have
a coordinated time system rather than setting their clocks loosely
according to the sun zenith. So the idea of time
zones was created to help keep people from missing their trains. Today,
the world has twenty four time zones, with all the
clocks in the same time zone displaying the same time,

(02:34):
but it can still be confusing, especially if you're trying
to schedule a phone call with someone in China or Australia.
How do you make sense of this? The easiest way
is to get out a globe and a table lamp.
The table lamp represents the sun position your globe, so
that England is pointing toward the sun. In this model,

(02:55):
it's now high noon in England. For historical reasons, the
zero degree longitude line runs through Greenwich, England. This is
called the prime meridian, and this place on the globe
is also known as GMT plus zero or a Greenwich
meantime or UTC plus zero, where UTC stands for coordinated

(03:16):
Universal Time. So look at your globe looking down at
the north pole. Imagine the globe divided into twenty four
pie shaped slices. Each slice is a time zone. It's
high noon in the England time zone. From the vantage
point of the North Pole. The Earth spins counterclockwise. That's
why the sun rises in the east and sets in

(03:38):
the west. In the slice immediately adjacent to England on
the left, it's one PM or UTC plus one. In
the slice immediately adjacent to England on the right, it's
eleven am or UTC minus one. As the Earth rotates counterclockwise.
In one hour, it will become high noon in the

(04:00):
slice immediately adjacent to England on the right. Five hours
after its high noon in England, the Earth will have
rotated enough for it to be high noon on the
East coast of the United States. This is referred to
as U t C minus five. The central time zone
of the U S is ut C minus six, Mountain
and Pacific are U t C minus seven and UTC

(04:23):
minus eight, respectively. Hawaii is U t C minus ten,
and finally Samoa is U t C minus eleven. The
International date Line is on the opposite side of the
globe from England, over near New Zealand. This first time
zone is ut C plus twelve. This is the first
time zone to see January one. Each new day starts

(04:47):
in the time zone adjacent to the International date Line
twelve hours before it's midnight in England, it's midnight in Auckland,
New Zealand, eleven hours after it's midnight in England, and
it's midnight in Samoa. Then the Earth rotates past the
International dateline. It becomes January second in New England, and

(05:08):
the cycle repeats. When you imagine how the globe rotates
with respect to the Sun like this, it's easy to
keep track of the time zones. Be sure to check
out our new video podcast, Stuff from the Future. Join
How Stuff Work staff as we explore the most promising
and perplexing possibilities of tomorrow. The How Stuff Works I

(05:30):
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