GEOG 140

Introduction to Physical Geography

Simplified Process for Determining Plane Arrivals

(omitting consideration of irregular time zone boundaries)

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  1. Find the nearest central meridian for each city (origin and destination). Assume it's the nearest even multiple of 15°.

  2. Draw a circle, showing Earth as seen from over the North Pole, as shown below. Place the Greenwich meridian (0°) to the right and the International Date Line (180°) to the left. The eastern hemisphere, then, is on top and the western is on the bottom.

    [ Earth from over North Pole ]

  3. Draw each city's central meridian on that diagram.

  4. Ask yourself: Is the International Date Line between the two cities on the shortest path between them?
    • Yes?
      • Imagine yourself over the equator, facing north between the two cities. Draw another diagram showing the International Date Line as a vertical line in the middle. Put another vertical line to the right of the Greenwich meridian to represent the city in the western hemisphere. Put a third vertical line to the left of the Greenwich meridian to stand for the city in the eastern hemisphere. Label all three lines.
      • Get the total longitudinal difference between the two cities by first subtracting each of their longitudes from 180° and then adding those two differences together.
      • Go to step 5.
    • No?
      • Ask yourself: Is the Greenwich meridian between the two cities on the shortest path between them?
        • Yes?
          • Imagine yourself over the equator, facing north between the two cities. Draw another diagram showing the Greenwich meridian as a vertical line in the middle. Put another vertical line to the right of the Greenwich meridian to represent the city in the eastern hemisphere. Put a third vertical line to the left of the Greenwich meridian to stand for the city in the western hemisphere. Label all three lines.
          • Get the total longitudinal difference between the two cities by adding their longitudes together.
          • Go to step 5.
        • No?
          • Imagine yourself above the equator, facing north between the two cities. Draw another diagram, showing the longitude of the more eastern city as a vertical line on the right side of the diagram. Show the longitude of the more western city as a vertical line on the left. Label everything.
          • Get the total longitudinal difference between the two cities by subtracting the smaller longitude from the larger.
          • Go to step 5.

  5. Divide the total longitudinal difference you calculated in Step 4 and divide it by 15° to get the time difference between the two cities. Note that, since we are using the cities' central meridians and standard time, the longitudinal differences will conveniently work out to even hours of time difference.

  6. Go back to your original circular diagram. Draw an arrow on the circle's circumference going from the city of origin to the city of destination.

  7. Ask yourself: Is the arrow pointing in a clockwise (>>>) direction or a counterclockwise (<<<) direction?
    • Clockwise?
      • You are going westbound, so subtract the time difference from the departure time (this gets you the time of departure in terms of the destination city's standard time).
      • Proceed to Step 8.
    • Counterclockwise?
      • You are going eastbound, so add the time difference from the departure time (this gets you the time of departure in terms of the destination city's standard time).
      • Proceed to Step 8.

  8. Add the flight time to the departure time (at destination, which you calculated in step 7) to get the arrival time in the destination city.

  9. Ask yourself: Did you cross the International Date Line?
    • No?
      • You are done
      • Call your loved ones to let them know when to collect you
    • Yes?
      • Ask yourself: Are you crossing the International Date Line westbound or eastbound? Remember, crossing the IDL westbound puts you in the eastern hemisphere and crossing it eastbound lands you in the western hemisphere.
        • Westbound?
          • Skip one full calendar day ahead
          • Inform your ride which time and day to get you
        • Eastbound?
          • Set the date one full calendar day behind
          • Inform your ride which time and day to get you (and you may even land on the day before you took off!

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This document is maintained by Dr. Rodrigue
Last Updated: 09/09/00

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