Transit Method Explorer

The planet crosses the exact middle of the star. Real transits usually cut across nearer the edge, which makes them shorter than this model predicts. Kepler-452b's real transit lasts 10.6 hours; a dead-central crossing would last 14.7.

The star is equally bright all over its disk. Real stars are dimmer at the edge than at the centre, so real light curves have rounded bottoms instead of flat ones. Flat bottoms are easier to measure, which is why the model keeps them.

The orbit is a circle and only two bodies matter. No other planets tug on it, and the star never wobbles.

Nothing here is drawn to scale between the star and the orbit. The telescope view is zoomed to the star's face. Judge sizes from the numbers, never from the picture.

depth = (R_planet / R_star)² — the fraction of the star's disk the planet covers. Depth depends on the ratio of the two radii and on nothing else: not the distance, not the star's mass.

P = √(a³ / M_star) — Kepler's Third Law, with P in years, a in AU and the star's mass in solar masses.

duration ≈ (P / π) × (R_star + R_planet) / a — how long the planet takes to cross. A bigger star takes longer to cross; a closer, faster planet crosses sooner.

Star radius, star mass, planet radius and period are read from the NASA Exoplanet Archive's composite parameters table, retrieved 3 November 2026. Orbital distance is then calculated from the period and the star's mass, so Kepler's Third Law holds exactly inside the model.

That calculation is not a shortcut. The archive's own listed distance for Kepler-5b, 0.0538 AU, does not agree with its own listed period and star mass, which together give 0.0506 AU. Measured values from different instruments rarely line up perfectly, and a model has to pick one set and stay consistent with it.

Depths the model calculates land a few hundredths of a percent off the archive's measured values, because real measurements include the edge-dimming and off-centre crossing this model leaves out.