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Difficulty: HardThe Earth as a Planet and Earth Movements

A weather monitoring station located at longitude 35∘E35^\circ\text{E} records local solar noon (12:00 p.m.12:00\text{ p.m.}) at the exact instant a UTC master clock displays 09:40 a.m.09:40\text{ a.m.} at the Greenwich Meridian (0∘0^\circ). At that identical moment, a remote research station records its local solar time as 06:20 a.m.06:20\text{ a.m.} on the same day. What is the longitudinal position of the remote research station?

  1. 50∘W50^\circ\text{W}Answer
  2. B
    50∘E50^\circ\text{E}
  3. C
    85∘W85^\circ\text{W}
  4. D
    15∘E15^\circ\text{E}

Answer

50∘W50^\circ\text{W}
The remote research station's local solar time (06:20 a.m.06:20\text{ a.m.}) is 3 hours and 20 minutes (200 minutes200\text{ minutes}) behind Greenwich Mean Time (09:40 a.m.09:40\text{ a.m.}). Since 1∘1^\circ of longitude equals 4 minutes of time, dividing 200 by 4 yields an angular difference of 50∘50^\circ. Because local time is behind Greenwich time, the station lies in the Western Hemisphere at 50∘W50^\circ\text{W}.

Step-by-Step Solution

1
Determine the time difference between Greenwich (0∘0^\circ) and the remote research station.
Greenwich Time = 09:40 a.m.09:40\text{ a.m.}, Remote Station Time = 06:20 a.m.06:20\text{ a.m.}. Time difference = 09:40−06:20=3 hours 20 minutes=200 minutes09:40 - 06:20 = 3\text{ hours } 20\text{ minutes} = 200\text{ minutes}.
Longitude calculations must be referenced against Greenwich Mean Time (0∘0^\circ Meridian) to determine absolute longitudinal position.
2
Convert the time difference into longitudinal degrees using the Earth's rate of rotation (1∘=4 minutes1^\circ = 4\text{ minutes}).
200 minutes4 minutes per degree=50∘\frac{200\text{ minutes}}{4\text{ minutes per degree}} = 50^\circ.
The Earth rotates 360∘360^\circ in 24 hours, which corresponds to 15∘15^\circ per hour or 1∘1^\circ every 4 minutes.
3
Determine the longitudinal hemisphere (East or West).
Since 06:20 a.m.06:20\text{ a.m.} is behind 09:40 a.m.09:40\text{ a.m.}, the remote station is West of Greenwich. Therefore, the position is 50∘W50^\circ\text{W}.
Places to the west of a given meridian experience local time earlier in the clock cycle (behind GMT), following the principle 'East gain, West lose'.

Key Concept

Longitude and Local Time Calculation across Meridians
Estimated Time:2m 0s
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Topics

The Earth as a Planet and Earth Movements

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