Question

It is 9:00 p.m. in Greenwich, England. You are on a ship whose local time is 6:00 p.m. What is the longitude of your ship?

Answer 1

Hint:
The horizontal circle that goes around the Earth are called the Latitudes and the semi-circles which connect pole to pole are called Longitudes. Every longitude cuts along every latitude.

Complete Step by Step Answer:
Longitudes are also called meridians. The total number of longitudes is 360. The longitude that passes through Greenwich, England is the $0^\circ $ meridian which is known as the Prime Meridian or the Greenwich Meridian. The longitudes are divided into two types i.e., the East longitudes and the West longitudes. The longitudes which run from $0^\circ $ to $180^\circ $ in east direction are called East longitudes. The longitudes which run from $0^\circ $ to $180^\circ $ in the west direction are called West longitudes. $0^\circ $ and $180^\circ $ longitudes do not have direction markers. All the other longitudes have direction markers, for example, $72^\circ {\text{E}}$ for $72^\circ $ East longitude, $120^\circ {\text{W}}$ for $120^\circ $ West longitude. Minutes and seconds can also be divided in each degree of longitude. The sun takes four minutes to move $1^\circ $ of longitude. If we travel from west to east, we gain four minutes as we cross every longitude and as we move from east to west we lose four minutes for each longitude we cross through. As time is less than the Greenwich time when we are on the ship, it means we have travelled in the direction of the West. The time is reduced by 3 hours i.e., by 180 minutes, it means we have travelled 45 degrees as the time is reduced by 4 minutes as we cross each latitude in the west direction. Hence, we are on 45 degrees’ west longitude.

Note:
The $180^\circ $ longitude is exactly opposite to the $0^\circ $ longitude and is called the anti-meridian. $82^\circ 30'$ Eastern Longitude is taken as the standard meridian of India and serves as the Indian Standard Time (IST). IST is exactly $5\dfrac{1}{2}$ hours ahead of Greenwich. Every country possesses its own standard time.