Which method detects exoplanets by measuring dips in a star's brightness?

The method that detects exoplanets by measuring dips in a star’s brightness is the transit method.

A transit occurs when a planet passes between its host star and Earth, blocking a small portion of the star’s light. Sensitive instruments record the resulting dip as a light curve. Repeated dips at regular intervals can reveal the planet’s orbital period, while the depth of the dip helps estimate the planet’s radius relative to its star.

The method works only when the planetary orbit is aligned favorably from Earth’s viewpoint, so most planetary systems do not show observable transits. Larger planets close to their stars are easier to detect because they block more light and transit more often. This creates an observational bias toward “hot Jupiters” and other short-period worlds.

Transit data can also support atmospheric studies when starlight passes through a planet’s atmosphere. Astronomers often combine the transit method with radial-velocity measurements: the transit supplies a radius, while the star’s gravitational wobble helps provide a mass. Together, these measurements can reveal a planet’s density.