Transit Photometry: Structures & Vocabulary

Transit photometry detects an exoplanet when it crosses the face of its star and blocks a measurable fraction of starlight. Repeated periodic dips reveal the orbital period, while the transit depth primarily constrains the planet-to-star radius ratio.

For a small dark planet crossing a uniformly bright star, the fractional light loss is approximately the square of the radius ratio. Real stars are limb-darkened and planets may have atmospheres, rings, spots, or companions that alter the simple shape.

Kepler and TESS have detected thousands of repeating transit signals. Follow-up observations reject eclipsing-binary false positives and combine transits with radial velocity or transit timing to measure masses.

A transit has ingress, full-transit phase, and egress. Depth, duration, impact parameter, limb darkening, eccentricity, and stellar density shape the light curve.