Geography : Longitude And Its Calculations

longitude definition and calculations

Previous Topic : Latitude And Its Calculations

Longitude

Longitude : are imaginary lines running from North to South.

Meridian Of Longitude

Meridian : are line, at right angle parallel through the poles.
Longitude of a place, is an angular distance of east or west of the greenwich meridian measured at the centre of the earth, there are 180° of east longitude and 180° of west longitude.
The longitude passing through Britain(London) and Accra (Ghana) is called the great prime or Greenwich meridian and it is inclined at longitude 0°.
Important lines on Longitude are 0°, Longitude 180W and longitude 180°E, etc.top↑

Important Of Lines Of Longitude

1] The lines of longitude along with the lines of latitude are used to determine the exact location of a place on the atlas map.
For example, Nigeria is located between longitude 3°E and 15°E of the greenwich meridian.

2] The lines of longitude are used to determine local time in relation to G.M.T which means Greenwich Mean Time, which is sometimes referred to as world time.top↑

Lines Of Latitudes And Lines Of Longitudes

Similarities Between Lines Of Latitudes And Lines Of Longitudes

1] Both are imaginary lines drawn on the globe.

2] They are both measured in degrees.

3] They are both used to determine the location of places on the map.

4] They both have Great Circle.

5] They are both used to calculate distance and measurement.top↑

Difference Between The Lines Of Latitudes And Lines Of Longitudes

1] lines of latitude run from west to east while lines of longitude run from north to south.

2] Lines of latitude are shorter towards the pole while lines of longitude are of the same length.

3] lines of latitude are parallel to each other while lines of longitude are not parallel to each other.

4] lines of latitude are called parallel while lines of longitude are called meridian.top↑

5] latitude has many great circle while longitude has only one circle.

6] latitude has the equator as its reference point while longitude has the greenwich meridian as its great circle.

7] Latitudes can only be measure from 0° to 180° while longitude can be measured from 0° to 360°.

8] lines of latitude are not used to calculate local time while lines of longitude are used to calculate local time.

9] lines of latitude are use to measure distance while lines of longitude are not use to measure distance.

10] lines of latitude do not meet at the pole while lines of longitude meet at the pole.top↑

Longitude And Time

During Rotation And Revolution of the earth, the earth passes through 360° in 24 hours, 15° in 1 hour or 1° in 4 minutes.
The Earth rotates from west to east, so every 15° towards the east, the local time advanced by 1 hour, and every 15° from east towards the west, the local time retard by 1 hour.top↑

Longitude Calculations Procedures

a] First locate the two places involved
b] find the longitude difference
c] Convert the longitude difference to time and,
d] Adjust the time according to the direction of movement, ( west or east).

Example 1

Mary starts her journey at longitude 0° and she’s moving towards eastward of longitude 10°. Calculate the time that mary will arrive at her destination.

Solution

Initial time = 12 noon
Destination = 10°E
Conversio of degree to time
1 hour = 15°
and 4 minutes = 1°
Hence 10° = (4 × 10) minutes
= 40 minutes
Destination time = Initial time + calculated time
= 12 noon + 40minutes
= 12:40pm

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Example 2

If the time at village A (long 75°W) is 5:00pm on Friday. Calculate the time and day at village B (long 120°E)

Solution

360° = 24hrs
15° = 1 hour
1° = 4 minutes
Village A = 75°W
Village B = 120°E

We will add ( west and east)
(75 + 120)° = 195°
195 divided by 15°
= 13hrs

Destination time = initial + calculated time
= 5:00 + 13 hrs
= 18:00
18:00 = 6:00
Ans = 6:00am on Saturday

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Example 3

Calculate the local time in New York (USA) longitude 75°W, when it is 10am in Nigeria of longitude 15°E

Solution

Initial time = 10:00am
New York = 75°W
Nigeria = 15° E
We will add ( west and east)
(75 + 15)° = 90°
90° divided by 15° = 6 hrs

Destination time = initial + calculated time
= 10:00am + 6hrs
= 14:00pm
14:00pm = 4:00pm
Ans = 4:00pm

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Example 4

An international match between Nigeria and South Africa is scheduled for 4pm on Saturday in Lagos, Nigeria 7°E, the reference is from Tanzania and the linesmen are from America.
Calculate the local time and day for radio listeners to listen to this match in
a] Accra, Ghana, of longitude 13°W
b] dares salam, tanzania of longitude 39°E
c] Florida, America of longitude 99°W

Solution

To find longitude difference
1) East to east or west to west = subtract
2)East to west or west to east = addition
3) Greenwich meridian west or east = addition.top↑

(a)
Accra, Ghana, longitude 13°W
Accra = 13°W
Lagos = 7°E
Longitude difference = 13° + 7° = 20°
15° of longitude = 1 hour
So you subtract 15° from the longitude difference

20° – 15° = 5°
That means there is 15° in your longitude difference which is equivalent to 1 hour
20° – 15° = 5°
Already show that there is 1hour advanced or retard in 20°,
So write that 1 hour to one side and continue

Time diff btw Lagos & Accra =
                                                        15°
                                                    = 0.333
0.333 × 1 hour ( not the 1 hour you kept, just part of the procedure)
1 hour = 60 minutes
Hence, 0.333 × 60 = 19.98
approximately to 20 minutes
Now add that 20 minutes to the 1 hour that you kept
1 hour + 20 minutes
= 1 hour 20 minutes
= 1hr 20mins top↑
Since Accra Ghana is located towards the west , the time will be behind, so we subtract
At 4pm as stated in the question
4pm = 16:00
So 16.00 – 1.20 = 14.8
And 14.8 = 2.40pm
Therefore the radio listeners will listen to the match by 2.40pm on Saturday.

(b)
Dares salam = 39°E
Lagos = 7°E
Longitude difference = subtraction ( east to east)
Longitude difference = 39° – 7° = 32°
Since 15° = 1 hour

So you start subtracting 15° from the longitude difference until you won’t be able to
You can also divided but not all the time is the longitude difference in whole number, so subtract insteadtop↑

32 – 15 = 17°
You subtract 15° from it again till you won’t be able to
17° – 15° = 2°
You can see now that you can’t subtract with 15° anymore, unless you want negative answer.

How many times did you subtract 15° from the longitude difference? 2 right,
Write that 2 to one side and continue,

17 – 15 = 2°

Time diff btw Lagos & dares salam =
                                                                    15°
                                             = 0.133
0.133 × 1 hour
1 hour = 60 minutes
0.133 × 60 = 8 minutes
= 8 minutes + the 2 hours that you kept
= 2 hours 8 minutes
= 2hrs 8minstop↑

Tanzania is located towards the east of Lagos so we add
4pm stated in the question + 2hrs 8mins
= 6:08pm on Saturday

(c)
Florida = 99°W
Lagos = 7°E
Longitude difference = 99° + 7° = 106°

Since 15° = 1 hour

So you start subtracting 15° from the longitude difference until you won’t be able to

If you start subtracting 15° from the longitude difference, you can only subtract 7 times which will give you 105top↑

Keep that seven to one side
106 – 105 = 1°

Time diff btw Lagos & Florida =
                                                           15°
                                      = 0.066
0.066 × 1 hour
1 hour = 60 minutes
0.066 × 60
= 4 minutes

4 minutes + the 7 hours that you kept
= 7hours 4minutes
= 7hrs 4 minutes

Florida is located in the west, so the time will be behind Lagos, hence will subtract

The 4pm stated in the question
4pm = 16:00
16.00 – 7.04 = 8.96
8.96 = 8hrs 96 minutes
8hrs 96minutes = 9 : 36minutes
Ans = 9 :36 am on Saturday.top↑

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