Astronomy6 min
Finding planets by the shadows they cast
The transit method has revealed thousands of worlds beyond our Solar System. It works by watching starlight dim, ever so slightly.
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When a planet passes in front of its star from our point of view, it blocks a tiny fraction of the starlight. Measuring these regular dips reveals the planet’s size and orbital period.
Combined with the radial velocity method — which detects a star’s wobble — astronomers can estimate a planet’s mass and density, hinting at whether it is rocky or gaseous.
During a transit, some starlight also filters through the planet’s atmosphere, allowing scientists to search for chemical fingerprints.
