How astronomers find planets by their shadow: the dip in starlight
30seconds
Most planets around other stars are far too faint to see directly, so astronomers watch the star instead. When a planet crosses its face, a tiny dark disc blocks a sliver of light, and the brightness dips by the ratio of the two areas: about 1% for a Jupiter, about 0.008% for an Earth.
Play with the planet's size, its orbit and its tilt, and see why most planets never line up and why one dip is only a rumour until it repeats.
Deep dive · 4 min
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