The idea is simple enough: monitoring a star for the dips in its brightness caused by a planet passing in front of it. In practice, however, such transit-based detection is like trying to tell when a seagull flies across the beam from a lighthouse. That's why it took astronomers years to convert the idea into a workable technique capable of finding not just gigantic planets, which block more than 1% of their star's light, but also planets the size of Earth. Their efforts have paid rich dividends, enabling the discovery of more than 231 exoplanets to date.
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