Mada za sehemu hiiUses Of MapsMada 3
- The Concept of Latitudes and Longitudes
- Uses of Latitudes and Longitudes
- Calculation of time at places on the map using longitudes
Longitudes enable people to calculate local time at different places on the Earth. It is important to understand basic rules that enable us to calculate local time by using longitudes. Moreover, it is important to understand ways of identifying a longitude of a particular place by using local time. You should understand that the complete rotation of the Earth on its own axis is equal to 360 degrees. The Earth takes 24 hours to complete that rotation. Therefore, the Earth takes one hour (or 60 minutes) to complete a rotation of 15 degrees. This means that when the Earth rotates on its own axis, it takes 4 minutes to rotate 1 degree (1°) of longitude. Therefore, we can understand the basic rules used to calculate time of a particular place as follows
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If the Earth takes 24 hours to complete one rotation of 360 degrees, how much time will it take to complete 15 degrees?
Solution:
360° 24 hours 15° hours?
Then, use the cross multiplication method (×)
15° × 24 hours 360° = 1 hour
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If the Earth takes one hour to rotate 15 degrees, how much time will it take to rotate one degree?
Solution:
15° 1 hour 1° hours?
Then, use cross multiplication method (×)
1° × 1 hour 15° 1 hour 15
Remember that 1 hour is equal to 60 minutes
Therefore, 60 minutes ÷ 15 = 4 minutes
The Earth therefore will take 4 minutes to rotate 1 degree.
According to these facts, the following time is taken by the Earth to rotate on its own axis in different degrees of longitudes:
- 4 minutes to rotate 1 degree (4 minutes = 1°)
- 1 hour to rotate 15 degrees (1 hour = 15°)
- 24 hours to rotate 360 degrees (24 hours = 360°)
These rules are important because they are used to calculate time of a particular place.
You can calculate local time of two areas that are located on the same side, that is; both on East or both on West of the Prime Meridian. Also, you can calculate local time of areas located in two different sides of the Prime Meridian that means one on the East and the other on the West.
Remember that when calculating time of two places located on the same side, for example, East to East, or West to West, you are supposed to find the difference of the degrees by subtracting the degrees of the two places. But when calculating the time between two areas located in two different sides, one on the East and the other on the West, you are supposed to add the degrees of the two places. This is due to the rotation of the earth on its axis. The more you move towards the East time difference increases while the more you move towards the West, time difference decreases. It is important to understand that the earth's rotation on its axis from West to East makes those on the eastern side of the Prime Meridian to experience sunrise and sunset earlier than those on the western side of the Prime Meridian.
Example 1:
If it is 9:00 A.M at town "A" located at longitude 30° East, what will be the local time at town "B" located at longitude 60° East?
Solution
Steps to follow:
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Find the difference in degrees of longitudes between town "A" and town "B". Since both towns are located in the Eastern side of the Prime Meridian, differences in degrees of longitude are found by subtracting the degrees of longitudes of the two towns.
60° – 30° = 30°
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Find the difference in time between town "A" and town "B". Since we don't have time of town "B" and the longitudinal difference between the two towns "A" and "B" is 30°, we can find the time by using the fact that, the Earth takes 1 hour to rotate 15 degrees.
1 hour 15° Hours? 30°
Then, use the cross multiplication method (×)
30° × 1 hour 15° = 2 hours
The difference in time between town "A" and town "B" is 2 hours.
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Find the time of town "B" by adding or subtracting the difference in time between town "A" and town "B".
Since town "B" is located East of town "A" hence, it is ahead in time.
Therefore, add the difference of 2 hours to the time of town "A" which is 9:00 A.M.
9 + 2 = 11
9:00 A.M + 2 hours = 11:00 A.M
Therefore, the local time of town "B" which is located on longitude 60° East will be 11:00 A.M
Example 2:
If the local time of town "C" located at 45° East is 1:00 P.M, what will be the local time of town "D" which is located at 15° West?
Solution:
Steps to follow:
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Find the difference in degrees of longitude between town "C" and town "D". Because these towns are located in two different sides of the Prime Meridian, that is East and West, the difference in degrees of longitude is found by addition.
45° + 15° = 60°
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Find the difference in time between town "C" and town "D". Since we do not have time of town "C" and the longitudinal difference between the two towns "C" and "D" is 60°, we can find it by considering the fact that the Earth uses 1 hour to rotate 15 degrees.
1 hour 15° Hours ? 60°
Then, use the cross multiplication method (×)
60° × 1 hour 15° = 4 hours
The difference in time between towns "C" and town "D" is 4 hours.
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Find the time of town "D" by adding or subtracting the difference in time between town "C" and town "D".
To find the local time of town "D", we subtract 4 hours from the time of town "C" which is 1:00 P.M. because town C is located on East while town "D" is located on West.
Thus, 1:00 P.M – 4 hours = 9:00 A.M
Therefore, the time at town "D" located at longitude 15° West will be 9:00 A.M.
Note: If the given time is of a place located on the West of the Prime Meridian, you are required to add the difference in time between town "C" and town "D" to get the time of a town located in the East of the Prime Meridian.
We can find the longitude of a place if time at the two places and the degrees of longitudes of one place are known.
Example 3:
Find the longitude of town "Y" whose local time is 3:00 P.M, if it is 1:00 P.M at town "Z" which is located at longitude 40° East.
Solution
Steps to follow:
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Find the difference in time between town "Y" and town "Z"
3:00 P.M – 1:00 P.M = 2 hours
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Find the difference in longitudes. Since we have the difference in time between town "Y" and town "Z", which is 2 hours, we can find the longitudes by considering the fact that the Earth takes 4 minutes to rotate 1°.
Convert the hours into minutes:
1 hour 60 minutes 2 hours minutes?
Then, use the cross multiplication method (×)
2 hours × 60 minutes 1 hour = 120 minutes
Convert the minutes into degrees
1° 4 minutes ? 120 minutes
Then, use cross multiplication method (×)
1° × 120 minutes 4 minutes = 30°
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Find the longitude of town "Y" by adding or subtracting the degrees obtained from the given degrees of town "Z".
Because the local time at town "Z" which is located at longitude 40° East is behind that of town "Y", we therefore, add 30° to the given 40° of town "Z".
40° + 30° = 70°
The longitude of town "Y" will thus, be 70° East.
Swali
The Earth takes 4 minutes to rotate how many degrees of longitude?
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