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Q 1. 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.
Answer:
| IDL | |
| 1500 W Meridian, Monday 15th August | 1500 E Meridian, Tuesday, 16th August |
| 800 W Meridian, Saturday, 24th December | 1700 E Meridian, Sunday 25 December |
Q 2. Select the correct option:
(1) While crossing the IDL, a person will have to add one day when travelling from
(a) East to West
(b) West to East
(c) South to North
(d) North to South
(2) If it is Wednesday 10 a.m. at 150 E meridian, then what will be the time at IDL?
(a) Wednesday 6 a.m.
(b) Wednesday 9 p.m.
(c) Thursday 2 p.m.
(d) Thursday 6 p.m.
(3) According to the international convention, at which meridian does the day and date change occur?
(a) 00
(b) 900 E
(c) 900 W
(d) 1800
(4) At which direction of the IDL does a new day start immediately?
(a) East
(b) West
(c) North
(d) South
(5) IDL brings coordination in which of the following?
(a) GPS system
(b) Defence departments
(c) Transportation schedules
(d) Determining the hemisphere
Answer 1: (a) East to West
Answer 2: (b) Wednesday 9 p.m.
Answer 3: (d) 1800
Answer 4: (a) East
Answer 5: (c) Transportation schedules
Q 3. Give geographical reasons
(1) IDL is proving to be very useful in today’s times
(2) The day starts in Pacific Ocean on the earth
Answer 1: The IDL brings coordination between international airlines, transportation service, economic and trade activities. It is important in today ’s modern era and rapidly happening global development so that we can keep a track of all the calculations of day and time accurately. With the help of IDl global transportation especially airways the schedules of the traffic worldwide are organised properly.
Answer 2: The IDL passes through the Pacific Ocean. With reference to the IDL the day on earth starts in the west and ends in the East. It is one and the same day only at 12 o ’clock midnight at the 180° meridian. For the countries lying to the east of it i.e. the USA, Chile, etc. it is the end of the day while for the countries lying to the west of it i.e. Japan, Australia, etc. it is the start of a new day. Thus, a new day starts in Pacific ocean on Earth.
Q 4. Write in brief:
(1) What considerations have been made while deciding the IDL?
(2) While crossing the IDL, what changes will you make?
(3) Why is the IDL not a straight line like the 1800 meridian?
(4) Why doesn’t the IDL pass through the land?
(5) Why is the IDL considered with respect to the 1800 meridian only?
Answer 1: Following points are taken into consideration while drawing an IDL
Answer 2: The International Date Line runs down the middle of the Pacific Ocean. If you cross the dateline moving east, you subtract a day, whereas if you are moving west you add a day. For example, if today is Friday and we crossed the International Dateline from west to east then it would be Thursday. If we went east to west it would be Saturday.
Answer 3: If the line was straight, then it could pass through some territories and island groups. This will result in the increase of a day on the same island and a country which would create a massive confusion among the civilians. To prevent this confusion, the line is deviated roughly following the 180° line of longitude.
Answer 4: If the International Date Line did cross land, people crossing the line would have to adjust their clocks by twenty-three hours! People on opposite sides of the line would disagree about what day it was. For some strange reason, none of the countries near the International Date Line wanted to subject their citizens to that sort of complication.
Answer 5:
According to the international conventions, the start of a date is considered to be at 180° meridian. This is because, when one crosses the 180° meridian from east or west, there is a difference of 12 hours from prime meridian. Accordingly, an adjustment or change in day time is made at 180° meridian. Due to these reasons, the IDL is considered with respect to the 180° meridian only.