CHAPTER 2: Latitudes and Longitudes
Obtaining Time from Longitudinal Values.
Longitudinal degree begins at Greenwich, Britain. This is the reference longitudinal line and all the time in the world are with respect to Greenwich time.
There are 360 longitudinal lines 1degree apart around the globe. The globe is divided into east hemisphere and west hemisphere.
So countries that lie to the east of Greenwich line are called E longitudinal line. For example India is 821/2 E to Greenwich. While NY is 74 W. So NY is west of Greenwich.
So how do we get the time.
Earth revolves 1 degree in 4 minutes. Based on this simple equation we will calculate how much ahead we are of Greenwich or how much behind we are of Greenwich.
Because Earth rotates from West to East so East Zone will be ahead of time then West Zone.
Now let us calculate for 4 cities how ahead the time is from greenwich and how back the time is from greenwich. If we know the time of our city and longitude value of any other city in the world we can know the time of that city using calculations shown below:
1) City New Delhi: Longitude - 77 degree E (i.e it is in Eastern Hemisphere)
1 degree --------- 4 minutes
77 degree --------? minutes
Cross Multiply and you get: 77 x 4 = 308 minutes which when converted into hours you get : 5.13 hours. So we know that New Delhi is ahead of London roughly 5.13 hours.
2) City of Hong Kong: Longitude - 114 degree E (i.e. it is in Eastern Hemisphere)
1 degree --------- 4 minutes
114 degree --------? minutes
Cross Multiply and you get: 114 x 4 = 456 minutes which when converted into hours you get : 7.6 hours. So we know that Hong Kong is ahead of London roughly 7.6 hours.
3) City of San Hose, USA: Longitude - 121 degree W (i.e it is in Western Hemisphere)
1 degree --------- 4 minutes
121 degree --------? minutes
Cross Multiply and you get: 121 x 4 = 484 minutes which when converted into hours you get : 8.1 hours. So we know that San Hose is behind London roughly 8.1 hours.
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3) City of NY, USA: Longitude - 74 degree W (i.e it is in Western Hemisphere)
1 degree --------- 4 minutes
74 degree --------? minutes
Cross Multiply and you get: 74 x 4 = 296 minutes which when converted into hours you get : 4.9 hours. So we know that NY is behind London roughly 4.9 hours.