Distant Worlds-transit method

Distant Worlds-transit method

diagram of transit method of finding the size of a distant planet

When a planet crosses in front of its star, as viewed by an observer, the event is called a transit. Transits by terrestrial planets reduce the star's brightness by about 1/10,000 for about two to 16 hours. By measuring the drop in brightness and knowing the size of the star, scientists can then determine the radius of the planet. The orbital period, or time it takes the planet to orbit its star, can be determined by measuring how much time elapses between transits. Once the orbital period is known, Kepler's Third Law of Planetary Motion can be applied to determine the average distance of the planet from its star.

IMAGE: NASA/Ames