Two boxes in different hemispheres are given in the following diagram. The IDL passes through both the boxes. In one box, the meridian, day and date is given. Find the day and date for the other box.

The earth rotates 360° in 24 hours, which means 15° in 1 hour.

360° = 24hours, then 360°/24hours = 15°.

Therefore in 1°, the earth takes 4 minutes.

60minutes/15° = 4 minutes. 1° = 4 minutes

The earth moves from west to east, therefore from 0° to east the time will be ahead and from 0° to the west the time will be behind

(A) When the 150° W Meridian is Monday and 15^th August then 150° E Meridian is Tuesday and the date will be 16^th August.

• This is because from moving from west to east the change in 1° will add 4 minutes to the area.

• Then the movement from 150° W Meridian to 150° E Meridian, the change is 300°. Therefore the 150° E is 20hrs ahead.

• According to the International Date Line (IDL), the person travelling from West to East should add a day. Therefore 150° E will be 16^th August, Tuesday.

(B) When the 170° E Meridian is Sunday 25^th December then 80° W Meridian will be 24^th December Saturday.

• The movement from east to west will reduce the time. By moving 1° there will be a decrease in 4 minutes.

• Then the movement from 170° E Meridian to 80° W Meridian will be 16 hrs behind.

• But according to International Day Line (IDL) person travelling from west to east should reduce a day. Therefore the date at 80° W meridian will be 24^th December, Saturday.