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Question

Difficulty: EasyLatitude, Longitude, and Time Calculations

If the local time at the Greenwich Meridian (0∘0^\circ) is 12:00 noon, what is the longitude of a city where the local time is 4:00 PM on the same day? Express your answer as a number in degrees East.

Answer: 60 degrees East

Answer

The longitude of the city is 60∘E60^\circ\text{E}.
The time difference between 12:00 noon and 4:00 PM is 4 hours. Since the Earth rotates 15∘15^\circ per hour, 4 hours corresponds to 4×15∘=60∘4 \times 15^\circ = 60^\circ. Because the local time at the city is ahead of Greenwich Mean Time (GMT), the city lies to the East of the Greenwich Meridian at longitude 60∘E60^\circ\text{E}.

Step-by-Step Solution

1
Determine the time difference between the two locations.
Time difference = 4 hours
Subtract 12:00 noon from 4:00 PM (16:00).
2
Convert the time difference into degrees of longitude.
Angular distance = 60∘60^\circ
Earth rotates 360∘360^\circ in 24 hours, which equals 15∘15^\circ per hour (4 hours×15∘=60∘4\text{ hours} \times 15^\circ = 60^\circ).
3
Determine the direction (East or West) relative to the Prime Meridian.
60∘E60^\circ\text{E}
Locations with time ahead of Greenwich are to the East.

Key Concept

Calculation of longitude from local time difference relative to Greenwich Meridian
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Topics

Latitude, Longitude, and Time Calculations

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