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How To Convert Local Mean Time to Greenwhich Mean Time (LMT to GMT)

The LMT of sunrise as tabulated in Nautical Almanac indicates 05h 15min. You are at longitude 099° 15' W. What will be the GMT of sunrise?

Given:
LMT of sunrise = 0552 H
         Longitude = 099° 15' W

What is asked:
                      GMT of sunrise

Analysis of the problem:

Our longitude is west. So the Greenwich Meridian is located east to us. And since the rotation of the earth around its axis is east to west, therefore, the Greenwich Mean Time is ahead to our Local Mean Time.

Solution:

Step 1. We have to divide our longitude by 15° to get how many hours the Greenwich Mean Time (GMT) is ahead to us. Why divide it by 15°? We have to divide the longitude by 15° because the earth rotates 15 degrees of an arc per hour. This is called converting arc to time.

099° ÷ 15° = 0637H

Step 2. We have to add 0637H to our LMT to get GMT because our longitude is west, that is to say, we are behind in time.

0637H + 0552H = 1229H is the GMT of sunrise.

LMT to GMT

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