## How to calculate time using longitudes?

Today we are going to learn how to calculate time using Longitudes. We know that our earth is spherical in shape. Therefore, somewhere it will be morning and somewhere it will be afternoon, evening or even night. So, if you are in India and you want to know the time in London or U.S.A., you can easily calculate with the help of longitudes. Remember, that latitudes have no role to play in time calculation https://ncert.nic.in/textbook/pdf/iess101.pdf.

But, before we start how to calculate time using Longitudes, let’s know a few basic things about longitudes and globe What are lines of latitudes and longitudes on Globe? .

## Calculating time with the help of Longitudes for Geography students

### Longitudes and Globe

There are 360 longitudes.

Longitudes run from 90° North Pole to 90° South Pole.

They are semi-circles.

Maximum distance between two longitudes are at the equator.

Our earth is spherical (round) in shape which is 360°

Earth takes 24 Hours to complete one rotation.

It means, we can say that 360° are covered in 24 hours.

Therefore, in 1 hour, earth will rotate 360 divided by 24 = 15°

So in 1 hour 15 degrees, 2 hours 30 degrees, 3 hours 45 degrees…………..and so on.

Now,

Let’s calculate in Minutes.

24 hours = 24 x 60 = 1440 minutes.

we can also say that earth completes one rotation (360°) in 1440 minutes.

So, how much time will it take to reach from one longitude to the other longitude?

1440 divided by 360 = 4 minutes.

Therefore, there is a time difference of 4 minutes between any two longitudes.

## How to calculate time using longitudes if a place lies in east?

This is the simplest way to calculate time.

You just have to remember that *there is a time difference of 4 minutes between any two longitudes*

You will understand better with some solved examples.

### Example No. 1.

**Question. **

**If the time at 0° Longitude is 7:00 a.m. What will be the time at **

**a) 2° East and **

**b) 26° East longitudes.**

### Solution a)

Given is, Time at 0° Longitude = 7.00 a.m.

To find is Time at 2° east Longitude ?

First you will see there are how many longitudes between the time given and time asked i.e. from 0 to 2.

Between 0° to 2°, there are total 2 longitudes, 1 and 2.

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 2° East longitude will be 4minutes x 2 = 8 minutes.

2° lies to the right (east) of 0°, so you will add 8 minutes to the given time.

Your answer will be 7:08 a.m.

### Solution b)

Given is, Time at 0° Longitude = 7.00 a.m.

To find is Time at 26° east Longitude ?

First you will see there are how many longitudes between the time given and time asked i.e. from 0 to 26.

Between 0° to 26°, there are total 26 longitudes, (1, 2, 3, 4, 5…………………..25, 26.)

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 26° East longitude will be 4minutes x 26 = 104 minutes which is equal to 1hr and 44 minutes.

26° longitude also lies to the right (east) of 0°, so you will add 1 hr. and 44 minutes to the given time.

Your answer will be 7:00 a.m. + 1 hr. 44 min = 8: 44 a.m.

## How to calculate time using longitudes if a place lies in the West?

### Question

**If the time at 0° Longitude is 4:00 a.m. What will be the time at **

**a) 8° West and **

**b) 35° West longitudes.**

### Solution a)

Given is, Time at 0° Longitude = 4.00 a.m.

To find is, Time at 8° West Longitude ?

First you will see there are how many longitudes between the time given and time asked i.e. from 0 to 8° West Longitude.

Between 0° to 8°, there are total 8 longitudes, (1, 2, 3, …………………..7, 8)

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 8° West longitude will be 4minutes x 8 = 32 minutes. .

8° longitude lies to the left (West) of 0°, so you will subtract 32 minutes from the given time.

Your answer will be 4:00 a.m. – 32 min = 3: 28 a.m.

### Solution b)

Given is, Time at 0° Longitude = 4.00 a.m.

To find is, Time at 35° West Longitude ?

First you will see there are how many longitudes between the time given and time asked i.e. from 0 to 35° West Longitude.

Between 0° to 35°, there are total 35 longitudes, (1, 2, 3, …………………..34, 35)

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 8° West longitude will be 4minutes x 35 = 140 minutes. .

35° longitude lies to the left (West) of 0°, so you will subtract 140 minutes which is equal to 2 Hr. and 20 minutes.

Your answer will be 7:00 a.m. – 2 Hr. and 20 minutes. = 4: 40 a.m.

## Calculating time if a place lies to the East and one in the West from the given longitude

Sometimes you may face difficulty in calculating time if one place lies to the east and the other in the west from the given longitude.

Try to understand to avoid any kind of confusion with solved examples.

### Question

If the time given at 50° East longitude is 11 a.m. What will be the time at

a) 10° East longitude

b) 60° East longitude and

c) 13° West Longitude.

### Solution a)

Remember, here time given is at 50° East longitude.

Therefore, 10° east will lie to the west of 50° E and 60°E will lie to the east of 50°

Given is, Time at 50° East Longitude = 11.00 a.m.

you have to find Time at 10° east Longitude which will lie to the left (west) of 50° East Longitude.

First you will see there are how many longitudes lie between the time given and time asked i.e. from 10° east to 50° east

Between 10° to 50°, there are total 50-10=40 longitudes.

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 10° East longitude will be 4minutes x 40 = 160 minutes, which is equal to 2 Hrs. and 40 minutes.

As 10° lie to the left (west) of 50° E, so you will subtract 2 Hrs. and 40 minutes from the given time.

Therefore, 11:00 a.m. – 2 Hrs. and 40 minutes = 8:20 a.m.

### Solution b)

Given is, Time at 50° East Longitude = 11.00 a.m.

you have to find Time at 60° east Longitude which will lie to the right (East) of 50° East Longitude.

First you will see there are how many longitudes lie between the time given and time asked i.e. from 50° east to 60° east

Between 50° to 60°, there are total 60-50=10 longitudes.

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 60° East longitude will be 4minutes x 10 = 40 minutes.

As 60° lie to the right (East) of 50° E, so you will add 40 minutes from the given time.

Therefore, 11:00 a.m. + 40 minutes = 11:40 a.m.

### Solution c)

Given is, Time at 50° East Longitude = 11.00 a.m.

you have to find Time at 13° West Longitude which will lie to the left (west) of 50° East Longitude.

First you will see there are how many longitudes lie between the time given and time asked i.e. from 13° West to 50° East

Between 13° to 50°, there will be total 50 + 13= 63 longitudes.

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 13° West longitude will be 4 minutes x 63 = 252 minutes, which is equal to 4 Hrs. and 12 minutes.

As 13° lie to the left (west) of 50° E, so you will subtract 4 Hrs. and 12 minutes from the given time.

Therefore, 11:00 a.m. – 4 Hrs. and 12 minutes = 6:48 a.m.

## How to calculate time to prove that IST is five and a half hour ahead of GMT

GMT is Greenwich Mean Time which lies at 0° Longitude (Prime Meridian)

IST is Indian Standard Time which lies at 82° and 30′ E (82 and 1/2 ° East)

Now,

Suppose the time at GMT ( 0° Longitude) is = 12.00 Noon.

you have to find Time at 82° 30′ East Longitude which will lie to the right (East) of 0° Longitude.

First you will see there are how many longitudes lie between the time given and time asked i.e. from 0° to 82° 30″ East.

Between 0° to 82° 30″ East., there will be total 0 + 82° 30″ = 82° and half longitudes.

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 82° 30″ East longitude will be 4 minutes x 82 = 328 minutes + 2 minutes for half degree extra, which is equal to 330 minutes.

330 minutes will be 5 hours and 30 minutes.

As 82° 30′ East Longitude lie to the right (East) of 0°, so you will add 5 hours and 30 minutes in the given time.

Therefore, time at 82° 30′ East Longitude will be 5:30 a.m.

## How to calculate the Longitude of a place with the help of given time?

### Question 1.

**Calculate the longitude of a place where the local time is 6:00 a.m., when the time is 9:00 p.m. at New Delhi on longitude 77° E**

Solution)

Time given at New Delhi (77° East) is 9:00 a.m. (Local time)

To find is the longitude of a place where the local time is 6:00 a.m.

Total time difference between New Delhi and of place B is 9:00 p.m. – 6:00 p.m.= 3 hours.

We know that between any two longitudes, there is a time difference of 4 minutes.

So, 3:00 hours is equal to 180 minutes.

180 divided by 4 is equal to 45.

Therefore, there will be a difference of 45 longitudes from New Delhi.

As the local time is less than the time of New Delhi, it means place B lies 45 Longitudes West of New Delhi (77° East)

45 Longitudes West of New Delhi (77° East) will be 77 – 45 = 32° East.

**Answer**: **Place B lies at 32° East Longitude where the local time is 6:00 a.m.**

### Question 2.

Calculate the local time at Singapore (104^{°} E) when it is 6:00 p.m. at Greenwich?

Solution:

Time given at Greenwich (0°) is 6:00 p.m.

To find the time at Singapore which is at 104**°** E.

First you will see there are how many longitudes between the time given and time asked i.e. from 0 to 104**°** E..

Between 0° to 104**°** E., there are total 104 longitudes, (1, 2, 3, 4, 5…………………..102. 103. 104)

We know that between any two longitudes, there is a time difference of 4 minutes.

Therefore, time at 104**°** East longitude will be 4 minutes x 104 = 416 minutes which is equal to 6hr and 44 minutes.

104**°** E. longitude also lies to the right (east) of 0°, so you will add 6 hr. and 44 minutes to the given time.

Your answer will be 6:00 p.m. + 6 hr. 44 min = 12: 44 a. m. (Night)

## Calculating time with the help of Longitudes for Geography students

### Challenging Question:

Two planes take off from Mumbai on 9th May, Sunday. at 5:00 a.m. Plane 1 flies over Arabian Sea, Europe, Atlantic ocean and reaches Western part of U.S.A. (California) after 12 hours. The other plane flies over Bay of Bengal, Japan, Pacific Ocean and also reaches California after 12 hours. On which day, date and time both the planes will reach California. **(suppose the time difference between India and California is of 12 hours).**

A) Sunday on 9th May at 5:00 P.M

B) Plane 1 will reach on Saturday at 5:00 p.m. (will loose one day) and plane 2 will reach on 10th May Monday at 5:00 a.m. (will gain one day)

C) Both the planes will reach on 10th May (Monday) Morning at 5:00 a.m.

D) Both the planes will reach on 9th May (Sunday) Morning at 5:00 a.m.

**Write your answers in the contact form given below**

#### Conclusion: How to calculate time using longitudes?

Calculating time with the help of Longitudes is interesting as well as useful. Hope you find this article on How to calculate time step by step interesting. Once you learn time calculation, teach two more people. It will make your understanding better and will help others as well.

There are many countries with many different time zones like Russia, Canada, U.S.A. etc. Today, in India also people of the North-East are demanding a separate time zone. Should India also have two time zones? Think about it’s pros and cons.

**You may like to read:**

International Date Line – why it is not straight?

Assam Tea Gardens Have Their Own Time

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