International Date Line 7

1. i. Greenwich Prime ii. 2011 iii. Davidson

2. (A) i. Wrong The dates change with respect to the 180 meridian only at those places on 180 meridian which coincide with the IDL. So basically, the dates change with respect to the IDL and not the 180 meridian.

ii. Wrong It is because of the IDL that the schedules of the traffic worldwide are organised properly.

iii. Wrong The direction of one’s travel was one of the considerations while deciding the IDL.

iv. Right

2. (B) i. The IDL has been made to pass through the Pacific Ocean.

ii. World Standard Time (GMT) is determined using the Greenwich Meridian or the Prime Meridian.

iii. In 1884, under the leadership of American professor Davidson, the representatives of many nations got together and decided the IDL.

iv. Indian Standard Time is 5 hours and 30 minutes ahead of Greenwich Mean Time.

v. The meridian 82°30' E longitude determines Indian Standard Time.

3. i. a. Maximum part of the IDL coincides with the 180 meridian which is a straight line. b. However, the IDL is not completely a straight line like the 180 meridian. c. This is because some land mass or some islands in the Pacific Ocean are in the way of the 180 meridian. d. Davidson and his team in order to avoid this made an attempt to make the IDL pass through the Pacific Ocean completely. e. As a result, the IDL turns east at some places, while it turns west at other places trying to avoid land mass or islands in the Pacific Ocean. Therefore, the IDL is not a straight line like the 180 meridian.

ii. a. While one travels from east or west, there is a difference of 12 hours from Prime Meridian (0 meridian) to the 180 meridian. b. Conventionally, the start (and end) of a date is considered to be at 180 meridian. c. The IDL is draw in such a way that its maximum part coincides with the 180 meridian; and to avoid the confusion in the day and the time on land, an attempt has been made to make the IDL pass through the Pacific Ocean completely. d. As per the international conventions, the day on the Earth starts in the West of the IDL and ends in the East of the IDL. As the IDL passes through the Pacific Ocean, the day starts in Pacific Ocean on the earth.

iii. a. Davidson and his team wanted to avoid passing of the IDL through land hence, an attempt was made to make the IDL pass through the Pacific Ocean completely. b. Had the IDL passed through any land mass or some islands, the people there would have had to follow different dates and timings because dates would have been different on their eastern and western parts. c. Also, it would have been difficult to synchronize the time and date when one crosses the IDL on land and when the date changes on the calendar. d. To avoid this problem, the IDL turns east at some places, while it turns west at other places. Therefore, the IDL doesn’t pass through land. 1  Std. IX: Perfect Notes Geography 4. i. a. We know that a 24-hour day starts at 12 midnight. However, the midnight occurs at different times at different places because of the earth’s rotation. b. This creates confusion of days, date and time. Hence, the IDL was created in order to avoid this confusion. c. It is an international convention to change the day and time while crossing the IDL. This helps in clearing the confusion of days, date and time globally. d. IDL is proving to be very useful to keep a track of all the calculations of day & time, especially in today’s modern era of rapidly happenings and global developments. e. The IDL is also useful for coordinating between international airlines, transportation services, economic and trade activities. f. It is only because of the IDL that the schedules of the traffic of global transportation worldwide are organised properly especially, with respect to the airways. Hence we can say that, the IDL is proving to be very useful in today’s times.

ii. The following considerations have been made while deciding the International Date Line (IDL): a. Direction of travelling: The direction of one’s travel i.e. from West of the IDL to East of the IDL or from East of the IDL to West of the IDL. b. The current day and date: The current day and date changes while crossing the IDL, as per the direction of travelling. For example, while travelling from west to east of IDL the same day should be considered after crossing the IDL. On other hand, while travelling from east to west of IDL, one day has to be added after crossing the IDL. c. Passes through Ocean: An attempt has been made to make the IDL pass through the Pacific Ocean completely. Had it passed through land or some islands, the people there would have had to follow different dates and timings because dates would have been different on their eastern and western parts. Also, it would have been difficult to know when one crosses the IDL on land and when the date changes on the calendar.