Partial darkness
In a partial eclipse , one celestial body is partially covered by another. The term is mainly used for solar and lunar eclipses , and less often for planetary coverages .
During a lunar eclipse , the maximum coverage only depends on the lunar orbit relative to the earth, but not on the observer's location. The darkness is total when the moon moves completely into the earth's shadow . It is partial when the moon is only partially in the umbra or even in the penumbra. Every lunar eclipse is the same for all observers for whom the moon is above the horizon.
In contrast, the course of every solar eclipse (and the rarer planetary eclipses) depends on the location of the observer.
Partially those frequent eclipses are called, in which the core shadow of the moon never hits the ground, but only his partial shade . Because it measures several thousand kilometers, such eclipses can be observed on up to a quarter of the earth's surface.
In a total eclipse, on the other hand, the umbra of the moon reaches the earth, but only along a narrow strip on the earth's surface. To the side of this totality zone , the darkness appears partially.
Strictly speaking, a distinction must therefore be made between a really total eclipse (with partial eclipse on the side) and a merely partial eclipse. With the latter, the decrease in brightness of the solar radiation is also only noticeable with a very high degree of coverage (over about 60%).
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If a planet is covered by the earth's moon , which happens every few months, the conditions are in principle comparable to the solar eclipse. But because the apparent lunar orbit by ± 1 ° depending on location of the earthly observer different runs, total eclipses are much more common than partial at the relatively small planet disk.
It is similar with the regularly occurring eclipses of the moons of Jupiter by the 20 times larger planet. They are gladly observed by amateur astronomers and were of great importance for seafaring until the development of accurate clocks . If, on the other hand, two moons of Jupiter cover or darken each other , this is usually only partially.