Maharashtra Board Class 9 Geography Chapter 7 International Date Line PDF Download

International Date Line

Let's Recall

Which meridian is used to determine World Standard Time (GMT)?

Which meridian determines Indian Standard Time (IST)?

What is the time difference between the GMT and the IST?

Which location bid farewell to the year 2016 the last of all?

On which day did that location welcome 2017?

What could be the reason behind the change in the day of Sydney and London?

Can You Tell?

We bid adieu to the year 2016 and welcomed the New Year 2017 on Saturday midnight. Similarly, other countries also welcomed the New Year. A table showing the days and time of the welcome of New Year in different countries and cities according to the Indian Standard Time is given. Observe the table and answer the following questions:

(Note: 24 Hour clock has been followed according to requirement in this chapter)

Which location was the first to welcome New Year in the world? What day was it then?

Try This

Complete the following table to understand the time at different meridians when its 12 noon at the Prime Meridian. Different meridians have different timings at the same time. For example, if it is 12 noon at prime meridian, then it is 8 am at 60°W and 1600 hrs at 60°E. Sunil and Meenal have to note these timings. Take the help of the figure alongside. After that, discuss in the class and answer the questions. Fill the boxes in fig 7.1.

Sunil and Meenal embark on their journey to circumvent the earth from 00° meridian at 12 noon on Thursday. During their journey, they cross each other at 180° meridian and move forward. When Sunil returns back to 00° meridian after his journey, he thought it was Friday. When Meenal returned at 00° meridian, she thought it is Wednesday. Now tell:

What is the day at 00° meridian at Greenwich after completing the table 'A'?

What is the day at 00° meridian at Greenwich after completing the table 'B'?

Though both were at the same place, why were they experiencing different days? How did this happen?

How many days occurred while doing this activity? Name them.

Teacher's Note

The Prime Meridian at Greenwich is the line from which all time zones start. Just like we use a common zero point for mathematics, Greenwich is the zero point for world time.

Exam Trick

Remember: When going east, time goes forward. When going west, time goes backward. Think of it like climbing a hill - east side is the future, west side is the past.

Points to Remember

The Prime Meridian (0°) is at Greenwich, England and is used to find World Standard Time (GMT).
The 82.5°E meridian passes through India and is used for Indian Standard Time (IST).
IST is 5 hours and 30 minutes ahead of GMT.
Time changes as you move east or west from the Prime Meridian.
Every 15 degrees of longitude means a change of 1 hour in time.

Teacher's Note

Two people traveling in opposite directions around the Earth will experience time differently. Like when you and your friend walk in opposite directions from school, you both reach different places at different times even if you walk for the same amount of time.

Exam Trick

Remember: Sunil went east so he had more Fridays, Meenal went west so she had more Wednesdays. East = extra day ahead, West = day goes backward.

Points to Remember

When traveling east, the day moves forward and comes earlier.
When traveling west, the day moves backward and comes later.
The 180° meridian is the International Date Line where day changes happen.
Traveling in opposite directions gives different calendar days.
Earth takes 24 hours to spin around, and we have 360 degrees, so 15 degrees = 1 hour of time.

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