International Date Line – why it is not straight?

Written By Avinash Sharan

4th January 2021

 International Date Line (IDL) shows the end of day one and the beginning of day two.

It is just like your wrist watch changes the day and date at 12;00 midnight.

We have to have a common point on earth from where the new day begins.

Therefore, 180° meridian is a common point of reference for the whole world.

When it is 12:00 midnight at 180° meridian, the day and date in the calendar changes.

We all have accepted this and named it as International Date Line (IDL).

In short 180° meridian (Longitude) is considered as the International Date Line (IDL).

Prime Meridian and International Date Line (IDL) divides the earth into two equal Hemispheres – Eastern and Western.

Here are some facts and frequently asked questions on International Date Line which everyone should know.

Frequently asked  questions on International Date Line




  1. What is International Date Line? 
  2. Why is it Important?
  3. Why is it not straight?
  4. What is International Date Line (IDL) and Prime Meridian?
  5. Can there be three consecutive days on earth near International Date Line (IDL)?
  6.  What about time at the poles?
  7.  Which country lies first after crossing the International Date Line?

1. What is International Date Line?

Have you ever thought what will happen if the day and date does not change?

Will it not lead to confusion all over the world?

Let’s understand this with an example.

Take a round white color plain ball or a balloon.

Rotate it.

Ask four people to count the number of rotation.

you will find that all four answers will be different.

Why so?

It is because in a plain white ball it is not possible to count the exact number of rotations.

Now draw a line (semi-circle) from North to South with a black/ red marker.

Once again rotate the ball and ask people to count.

This time all answers will be the same.

Therefore, International Date Line at 180° meridian is a universally accepted indicator which indicates one complete rotation of the earth.

You may call it as the start and the end point.

To start from there and to reach back at the same point, the earth takes 24 hours.

This 24 hours is what considered as one day on earth.

So, we can say that International Date Line (180° Longitude) serves as the line of demarcation between two consecutive calendar datesAssam Tea Gardens Have Their Own Time

2. Why is it important?

As mentioned above, International Date Line (IDL) is an indicator which shows one complete rotation of earth.

Now, as we know that it takes 24 hours to complete one full rotation (360°), it is easy to know how much it rotates in one hour, two hours, three hours etc.

In this way, the whole earth was divided into 24 time zones.

When we divide 360 by 24 we get 15. What does it mean?

It means the earth reaches from 0º to 15º in one hour,

From 15º to 30º in two hours and so on.

With the help of this formula, clocks were designed.

Therefore, we can say that International Date Line (IDL) has helped us to keep the record of time.

Today, we know what is the time at which place and there is absolutely no confusion about time, date and day.

3. Why is International Date Line not straight?

You can easily understand this from the incident given below.

A straight line between India and Pakistan could have divided the country between two parts.


But it was not done.


Lord Mountbatten had drawn the borders – and he based it on the latest census information he had with him.

This helped him determine which villages were Muslim-majority and which had Sikh & non-Muslims as majority.

What does it mean?

It means that few things are considered before a line is drawn.

Similarly, many factors were considered before drawing the International Date Line (IDL).

Our earth is spherical in shape i.e. 360°.

At every degree there is a line from North to South which are called longitude.

All these semi circular lines are straight except the 180° Longitude.

There is a valid reason behind it and it is very simple.

Let’s understand this with an example.

Suppose you have a house which has two rooms.

A line passes through the center of your house.

Now, the room to your left is one hour ahead of the other room.

Will it be convenient for you or you will have difficulty in managing?

Think practically.

This is what happened when the people were deciding to draw the International Date Line (IDL)

The same type of problem will occur if a small island has two different times.

To avoid any confusion of date, day and time, this line is drawn through where the sea lies not the land.

That is why 180° Meridian is not straight, it goes zig-zag.

4. What is International Date Line and Prime Meridian?


  THE ZIG-ZAG INTERNATIONAL DATE LINE            Courtesy: maritime professional

If you want to pin point a location on the globe, you definitely need a reference point.

In case of latitudes, it was easy to draw the starting point.

People made a line (circle) at the center of the earth and named it as Equator.

But it was not so easy to draw a line from North to South as starting point because all the lines look similar.

Now, how to select a starting point in case of Longitudes ?

Greenwich is a place near London which has a “Royal Observatory

Most of the Geographers  were also working at the Royal Observatory.

They decided that the Longitude which passes through Greenwich, can be considered as the starting point.

Moreover, at that time Great Britain was also a very powerful country.

It was accepted by all members, and was named as 0° Longitude or the Prime Meridian.

Keeping 0° Longitude as the reference point, all other 360 longitudes/meridians were drawn.

To the opposite of 0° longitude, lies 180°. which is considered as the International Date Line (IDL)

5. Can there be three consecutive days on earth near International Date Line (IDL)?

Is it possible to have Sunday, Monday and Tuesday together on earth?


It is not only possible but it happens everyday near the International Date Line (IDL).

Let’s understand this with an activity.

We know that the 180°meridian (IDL) is not straight, it is zig-zag.

As we all know that there are two days at the same time on earth.

When it is Sunday morning in India, it is Saturday in U.S.A.

Now a moment will come, when it is about to be Monday in Kiribati islands.

The moment that happens, it is still going to be Sunday in most of the world, because our time zones shift time backwards.

However, at Howard island, it will still be Saturday because of a difference of more than 24 hours when comparing the two extreme time zones.

All this happens between 10:00 UTC and 11:59 UTC.

During this time three different calendar days and dates exist at different places on earth.

6. What about time at the poles?

Do you know that poles are also called as timeless and space-less?

Surprised? Does it mean that there is no time?

How do the people know about the time there?

You know that our earth is tilted and all longitudes meet at the poles.

Now, if the North pole is tilted towards the sun and you are standing at the North Pole, you will see the sun continuously for 24 hours at the same place in spite of the rotation of the earth.

It means there is no sunrise and no sunset.

That is why Norway is known as the “land of Midnight Sun.

When there is no sunrise and no sunset, there is no question of morning, afternoon, evening and night because the sun is visible even at midnight.

Therefore, it is called timeless.

As the North and South pole are just a small point where all the longitudes meet, so, there is no space.

That is why it is also known as space-less.

The scientists who go to the poles for research work, they follow their watch for the time.

The nature does not indicate the time but their watch indicates.

They adjust their daily routine according to their watch.

Date Line at the poles become meaningless.

7. Which country lies first after crossing the International Date Line?

You know that as soon as you cross the 180°meridian, the date changes.

The first visible land will be of Siberia (Russia).

But, no one lives in that part of Russia.

After that the land visible will be Japan.

Do people live in Japan?क्यों आते हैं जापान में भूकंप-ज्वालामुखी-सुनामी ?

Yes, of course.

so, the people  of Japan will be the first to see the sun.

That is why Japan is called the “The Land Of Rising Sun.”

But wait, do you think that Japanese are the first to see the rising sun today also?


To the east of Japan lies many small islands in the Pacific such as Gilbert, Phoenix , Line etc.

One such island country is Kiribati which lies just to the west of 180° meridian.

These islands were inhabited earlier but today there are people who live on these islands and they are the one who witness the first rays of sun.

Many tourists visit Kiribati islands to witness the rising sun in the new year.

Therefore, Kiribati islands is the true land of rising sun.

In India, the first ray of sun can be seen from the Andaman and Nicobar islands अंडमान और निकोबार द्वीप समूह.

Have you heard about the NEW EIGHTH CONTINENT – ZEALANDIA in the Pacific.


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