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Orbital factors affecting moonrise and moonset |
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ORBITAL FACTORS AFFECTING MOONRISE AND MOONSETTwo factors in the Moons orbit change the times of moonrise and moonset on a daily basis: (1) the Moons orbital angle and (2) its orbital speed.Orbital Angle The Moon crosses the equator twice during each revolution. It crosses the equator while moving north and crosses it again while moving south during each revolution. The angle at which the Moon crosses the equator is known as the Moons ecliptic orbit angle. This angle varies between 18 1/2 and 28 1/2 over a period of a little more than 18 years. The mean angle is 23 1/2. This variation is illustrated in figure 6-8-4.
Figure 6-8-2.-Earth-Moon-Sun relationship during Full Moon phase.
Figure 6-8-3.-Moon phases through one complete revolution of Earth.
Figure 6-8-4.-Ecliptic Moon orbit. When the Moons orbit is above the Northern Hemisphere, moonrise is earlier in the north and later in the south. Conversely, when the orbit is above the Southern Hemisphere, moonrise is earlier in the south and later in the north. The Moons orbital angle causes the times of moonrise and moonset to vary greatly between the extreme north and south latitudes, while at low and mid latitudes, the time differences are slight. In low and middle latitudes, moonrise and moonset occur about 50 minutes later each day. |
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