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why does the moon turn red during a lunar eclipse
In a lunar eclipse the Sun, Earth and Moon line up, with Earth in the middle. Earth blocks the direct sunlight that normally lights the Moon.
So you would expect the Moon to vanish into the shadow, black as night. It does not. It glows a coppery red, so Earth's shadow is not truly empty.
The secret is Earth's air. Sunlight skimming past our planet's edge passes through a thin ring of atmosphere, and the air bends that light inward, into the shadow.
On the way, the air scatters away the blue light, almost six times more strongly than red. What survives is red and orange, and it falls on the Moon.
So a red Moon is every sunrise and sunset on Earth, at once, painted onto the Moon. Dust or smoke in our air makes it darker, so no two eclipses match.
A blood-red Moon is not a warning from the sky, just every sunset on Earth glowing at once.