Scheduled air date: 2001 Jan 08-14
As with all of the planets in the solar system, the Earth has an elliptical ("flattened" circle) orbit with the Sun slightly off-center. Because of this— in accordance with Kepler's Second Law of Planetary Motion—the Earth moves more quickly when it is nearer the Sun than when farther from it. As illustrated above, the Earth is at perihelion—closest to the Sun—in Winter, during the first week of January. Therefore, the Earth is moving most rapidly in Winter and completes that season (one quarter of its orbit) in only 89 days.
The Earth is farthest from the Sun in Summer (during the first week of July) and moves at its slowest. Therefore it takes the Earth almost 94 days to complete the Summer quarter of its orbit.
(Seasonal references are for the Northern Hemisphere, and would be opposite for the Southern Hemisphere.)
If you wish to view illustrations for other episodes, please see our Star Gazer Illustrated directory.
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