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Difficulty: EasyThe Earth as a Planet and Earth Movements

Due to the Earth's rotation from west to east, local solar time varies with longitude across the globe. Arrange the following longitudes in order of their local solar time at any given moment, from the EARLIEST time of day to the LATEST time of day.

  1. 190∘W90^\circ\text{W}
  2. 230∘W30^\circ\text{W}
  3. 345∘E45^\circ\text{E}
  4. 4120∘E120^\circ\text{E}

Answer

The correct sequence from earliest to latest local time is 90∘W90^\circ\text{W}, 30∘W30^\circ\text{W}, 45∘E45^\circ\text{E}, and 120∘E120^\circ\text{E}.
Because the Earth rotates on its axis from West to East at a rate of 15∘15^\circ per hour, local solar time increases as you move eastwards. Therefore, the longitude located furthest west (90∘W90^\circ\text{W}) has the earliest time of day, followed by 30∘W30^\circ\text{W}, then 45∘E45^\circ\text{E}, and finally the longitude furthest east (120∘E120^\circ\text{E}) which has the latest time.

Step-by-Step Solution

1
Identify the relationship between Earth's rotation direction and local time.
Earth rotates from West to East, meaning eastern longitudes experience sunrise earlier and are ahead in time, while western longitudes are behind in time.
The sun appears to rise in the east and set in the west due to Earth's axial rotation.
2
Compare longitudes relative to the Greenwich Meridian (0∘0^\circ).
Longitudes in the Western Hemisphere (W\text{W}) are behind 0∘0^\circ, while longitudes in the Eastern Hemisphere (E\text{E}) are ahead of 0∘0^\circ.
Moving west reduces local solar time (1∘=4 minutes1^\circ = 4\text{ minutes} behind), whereas moving east increases local solar time (1∘=4 minutes1^\circ = 4\text{ minutes} ahead).
3
Order the given longitudes from furthest west to furthest east.
90∘W→30∘W→45∘E→120∘E90^\circ\text{W} \rightarrow 30^\circ\text{W} \rightarrow 45^\circ\text{E} \rightarrow 120^\circ\text{E}.
This spatial progression from west to east directly corresponds to chronological progression from earliest hour of the day to latest hour.

Key Concept

Earth's West-to-East rotation causes places located further East to have a local time ahead of places located further West.
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Topics

The Earth as a Planet and Earth Movements

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