Moon in its elliptical orbit, the distance between the Moon and Earth varies. It is this difference in distance that controls the Moons orbital speed. When the distance between the Moon and Earth decreases (B), the Moon orbits at a faster rate of speed; and when the distance increases (A), it orbits at a slower rate of speed.

The point in the Moons orbit that is closest to Earth is known as perigee, and the point farthest away is known as apogee. At perigee, the Moon is traveling at its fastest rate of speed. At apogee, it is traveling at its slowest rate of speed. Figure 6-8-6 illustrates the distance traveled in 1 day at apogee and perigee. The distance between A and B is greater than the distance between A and B, because of the Moons faster orbital speed at this point in its orbit (perigee).

Because of the Moons faster orbital speed at perigee, moonrise when the Moon is at point B occurs more than 50 minutes later than when the Moon is at point A. Remember, at low and mid latitudes, the Moon rises APPROXIMATELY 50 minutes later each day. At point B, moon-rise occurs less than 50 minutes later than at point A.

Learning Objective: Identify the source providing specific times of moonrise and moonset.

Tables and figures in Air Almanac are used to obtain specific times of moonrise and moonset. The Almanac contains Moonrise and Moonset tables, a table for interpolating moonrise and moonset for longitude, and the Conversion of Arc to Time table.

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