How dark can it get on Earth during a solar eclipse?
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The moon has a monthly orbital cycle around Earth. If the moon had a circular orbit that was in the same plane as Earth’s orbit around the sun, there would be monthly solar and lunar eclipses. But the moon’s orbit is tilted with respect to Earth’s orbit, so the sun-Earth-moon alignment is only very infrequently perfect enough to create an eclipse. The moon’s elliptical orbit causes its distance from Earth to vary. When it is closer, the path of totality is wider and eclipses last longer. When it is farther from Earth the moon can’t cover the entire sun and an annular eclipse is seen. In an annular eclipse the moon covers all but a thin circular ring of the sun.
Some observers reported that they saw Venus and some of the brighter stars during a total solar eclipse. It is not entirely dark, however, because light comes from the sun’s corona, the extremely faint glow surrounding the sun that is produced by ionized gases emitted by the sun. More light may come from reflection of light by the atmosphere in nearby areas not in the path of totality. The complete eclipse of the sun lasts for an average of about 2.5 minutes, but can last over 7 minutes.