transit photometry

astronomy

Also known as: photometric transit method

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July 19, 2026

Quick Summary

In astronomy, a transit occurs when a smaller celestial body passes across the disk of a larger one, obscuring a small portion of it. This phenomenon is observed when planets like Mercury or Venus transit the Sun, or when a moon transits its planet.1

Transit photometry is a key method for discovering extrasolar planets. When a planet passes in front of its star from our perspective, it causes a slight, temporary dip in the star's brightness. By measuring these dips, astronomers can determine the planet's size and orbital period. This technique has been instrumental in discovering thousands of exoplanets, including those found by missions like Kepler and TESS.2

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extrasolar planet
Detection of extrasolar planets
A complementary technique is transit photometry, which measures drops in starlight caused by those planets whose orbits are oriented in space such that they periodically pass between their stars and the telescope; transit observations reveal the sizes of planets as well as their orbital periods. Radial velocity data can…
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A complementary technique is transit photometry, which measures drops in starlight caused by those planets whose orbits are oriented in space such that they periodically pass between their stars and the telescope; transit observations reveal the sizes of planets as well as their orbital periods. Radial velocity data can…
Read More