Transit Photometry: Observation, Measurement & Evidence

A transit light curve includes ingress, a central transit interval, and egress. Its depth, duration, shape, timing, and recurrence depend on planet radius, stellar radius, orbital period, impact parameter, eccentricity, and limb darkening.

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.

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.

Repeated dips, consistent periods, color behavior, centroid tests, and follow-up spectroscopy reject many false positives. Kepler and TESS demonstrated the method at enormous statistical scale.