What Are Time Zones?
By Cindy Grigg
1
Time zones are based on the position of the
sun. We say that 12 o'clock noon is midday. The
sun is at its highest point, directly overhead. The
Earth spins or rotates on its axis, like the
spinning of a top. As the Earth spins, the sun
looks like it moves across the sky from east to
west.
2
It takes the Earth about 24 hours to make
one rotation. This causes day and night. When
one side of the Earth is turned toward the sun, it
is day. On the other side of the Earth, it is nighttime.
The Earth's surface can be thought of as a giant circle. Circles can be
3
measured in degrees. One whole circle is made up of 360 degrees. It takes the
Earth 24 hours to turn in a circle. So when we divide 360 degrees by 24 hours, we
see that the Earth rotates about 15 degrees each hour.
4
Each time zone is set up having 15 degrees of longitude. Longitude lines are
the LONG lines you see on a globe. They run from the North Pole to the South
Pole. They are like the LONG sides of a ladder. There are twenty-four time zones
around the world.
Lines of longitude are also called meridians. This word came from the Latin
5
word for midday. The sun crosses the meridians or lines of longitude at midday, or
halfway between the times of sunrise and sunset. This is where we get the
abbreviations for time of A.M. and P.M.
A.M. stands for "ante-meridian," which means "before midday" or before the
6
sun crosses the meridian (line of longitude). P.M. stands for "post-meridian," which
means "after midday" or after the sun has crossed the meridian.
One special line of longitude is called the International Date Line. It is the line of
7
180 degrees longitude. It is special because each day begins at this line. On the
east side of this line, it is late night on Sunday. On the west side of this line, it is
early morning on Monday. When you travel west across the IDL, you gain a day.
When you travel east, you lose a day.
This line was chosen because it passes through the fewest land areas on Earth
8
where people live. It would be very confusing if you lived in a country that was
divided by the International Date Line. It would be Sunday in one part of your
country. It would be Monday in the other part. To make sure this doesn't happen,
the International Date Line is not a straight line. If you look at a globe, you will see
that this line zigzags around any land areas. It does not pass through them.
9
Inside each time zone, most places have the same time. New York City in the
United States, in North America, and Lima, Peru, in South America, have the same
time. This is because they are both within the same time zone or between the
same two lines of longitude.
Most time zones follow the lines of longitude. Some cities have a line of
10
longitude passing through them. These cities have had to choose one time zone or
the other to follow. This makes life easier if the same time is followed throughout
the city.
The United States has four time zones for the 48 contiguous states. These are
11
the states that make up the continental U.S. Alaska and Hawaii are farther west.
They fall in between other lines of longitude. They have two different time zones.
So all 50 of the United States fall into six different time zones.
What Are Time Zones?
By Cindy Grigg
Times post-meridian Based
Contiguous Time Same
Divided Passing Continental
Pass Longitude Across
ante-meridian Passes Divide
Rotation Zones Between
Zone Gain
Directions: Fill in each blank with the word that best completes the reading
comprehension.
Time zones are (1) BASED on the position of the sun. We say that 12 o'clock noon is
midday. The sun is at its highest point, directly overhead. The Earth spins or rotates on its
axis, like the spinning of a top. As the Earth spins, the sun looks like it moves (2) ACROSS
the sky from east to west.
It takes the Earth about 24 hours to make one (3) ROTATION. This causes day and
night. When one side of the Earth is turned toward the sun, it is day. On the other side of
the Earth, it is nighttime.
The Earth's surface can be thought of as a giant circle. Circles can be measured in
degrees. One whole circle is made up of 360 degrees. It takes the Earth 24 hours to turn in a
circle. So when we(4) DIVIDE 360 degrees by 24 hours, we see that the Earth rotates
about 15 degrees each hour.
Each time (5) ZONES is set up having 15 degrees of longitude. (6) LONGITUD lines
are the LONG lines you see on a globe. They run from the North Pole to the South Pole.
They are like the LONG sides of a ladder. There are twenty-four time zones around the
world.
Lines of longitude are also called meridians. This word came from the Latin word for
midday. The sun crosses the meridians or lines of longitude at midday, or halfway (7)
BETWEEN the (8) TIMES of sunrise and sunset. This is where we get the abbreviations
for time of A.M. and P.M.
A.M. stands for (9) “ANTE – MERIDIAN” which means "before midday" or before the
sun crosses the meridian (line of longitude). P.M. stands for "(10) POST-MERIDIAN,"
which means "after midday" or after the sun has crossed the meridian.
One special line of longitude is called the International Date Line. It is the line of 180
degrees longitude. It is special because each day begins at this line. On the east side of this
line, it is late night on Sunday. On the west side of this line, it is early morning on Monday.
When you travel west across the IDL, you (11) GAIN a day. When you travel east, you
lose a day.
This line was chosen because it (12) PASSES through the fewest land areas on Earth
where people live. It would be very confusing if you lived in a country that was (13)
DIVIDED| by the International Date Line. It would be Sunday in one part of your country.
It would be Monday in the other part. To make sure this doesn't happen, the International
Date Line is not a straight line. If you look at a globe, you will see that this line zigzags
around any land areas. It does not (14) PASS through them.
Inside each time zone, most places have the (15) SAME time. New York City in the
United States, in North America, and Lima, Peru, in South America, has the same time.
This is because they are both within the same time zone or between the same two lines of
longitude.
Most time zones follow the lines of longitude. Some cities have a line of
longitude (16) PASSING through them. These cities have had to choose one (17) TIME
zone or the other to follow. This makes life easier if the same time is followed throughout
the city.
The United States has four time (18) ZONES for the 48 (19) CONTIGUOUS states.
These are the states that make up the (20) CONTINENTAL U.S. Alaska and Hawaii are
farther west. They fall in between other lines of longitude. They have two different time
zones. So all 50 of the United States fall into six different time zones
