RAS question
The International Date Line (IDL) roughly follows which longitude?
Correct answer: (B) 180 degrees.
The International Date Line roughly follows the 180-degree longitude line through the mid-Pacific Ocean.
Explanation
The International Date Line is linked to the 180-degree meridian because it lies halfway around the world from the Prime Meridian at 0 degrees longitude in Greenwich. NOAA describes it as passing through the mid-Pacific Ocean and roughly following a north-south 180-degree longitude line on the Earth's surface. It is not a perfectly straight meridian: the line bends around political borders, so countries and territories are not split into different calendar dates. The date-change rule is the key practical point. Crossing the IDL westward makes the calendar one day later, while crossing it eastward moves the date one day back.
Why the other options are wrong
- (A) 90 degrees E is not the IDL because the question's reference line is the 180-degree meridian, while 90 degrees E passes through eastern India.
- (C) 90 degrees W is not the IDL because it lies in the Americas, not on the mid-Pacific 180-degree line described for the date line.
- (D) 0 degrees is the Prime Meridian through Greenwich, whereas the IDL is roughly halfway around the world at 180 degrees longitude.
Concept
This tests the world geography concept of longitudes and global time reckoning. It recurs in RAS because the IDL connects map reading with calendar change, a standard physical geography application.