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- When
it's midday on one half of the Earth, it's midnight on the other half.
- The
line between darkness and daylight seems to move like the hands on a
clock.
It even moves clockwise around the Earth. That's no coincidence! Read on . . .
The
"Why" Behind What You See
The Earth rotates on its axis. It makes one full turn every 24 hours.
As it turns counterclockwise (toward the east), new places enter the sun's
light (sunrise). On the other side of the globe, new places leave the
sun's light (sunset).
Our
clocks show these 24 hours, too. Most are divided into 12 a.m. and 12
p.m. hours (black numbers). When we want to use a standard time that's
the same everywhere on Earth, we use Greenwich
Mean Time (GMT), also called Universal Time (UT). This is based on
a 24-hour clock (red numbers).
We've also divided earth into 24 time zones. All clocks in the same time
zone show the same time. Each time zone is an hour earlier than next zone
east and an hour later than next zone west. On the equinox, as shown in
the animation above, each hourly movement of the sun roughly shows the
movement from one time zone to the next.
Think! What time is it now in your classroom? What time do you think it is in a classroom that is two time zones west of you?
Math Challenge: Each day, the earth rotates once on it's axis, which equals 360 degrees. There are 24 hours in a day. How many degrees longitude does the earth turn each hour? The earth is also divided into 24 global time zones. How many degrees of longitude does each one cover? (See answer, below.)
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Answer: 360 degrees ÷ 24 hours = 15 degrees per hour. So each time zone covers 15 degrees of longitude.
