Transit

Definition

In astronomy, a transit is the passage of a smaller body across the face of a larger one as seen by an observer — for example, a planet crossing the Sun's disk, or an exoplanet passing in front of its host star.

In context

When an exoplanet transits its star, it blocks a tiny fraction of the star's light, producing a small, repeating dip in brightness. Measuring these dips is one of the most productive methods for discovering and characterizing planets around other stars.

Astrology — a separate, interpretive tradition — uses the word differently, to describe the current positions of the planets relative to a person's birth chart.

Related ideas

From Earth, only Mercury and Venus can transit the Sun, because they are the only planets that orbit closer to the Sun than we do. Space telescopes have used the transit method to find thousands of exoplanets.