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    Stars & exoplanets

    Exoplanet Transit Depth Calculator

    Fractional dimming when a planet crosses its star — the basis of Kepler and TESS discoveries.

    δ = (R_p / R_★)²

    Inputs

    Results

    Transit depth
    83.86 ppm (0.008386 %)
    Depth as a fraction
    8.38632 × 10^-5 ×
    Radius ratio k = R_p/R_★
    0.0091577
    Brightness during transit
    99.99161 % of normal
    Worked solution
    1. k = 6,371,000 / 695,700,000 = 0.00915768
    2. δ = k² = 8.38632 × 10^-5

    How the result changes

    Depth (×) plotted against Planet radius (Earth radii), from one quarter to four times your input, with your input marked.00.00050.0011234Planet radius (Earth radii)Depth (×)your input
    Depth vs planet radius

    How it works

    An Earth-size planet crossing a Sun-like star blocks about 84 parts per million of its light; a Jupiter blocks about 1%. Space telescopes such as Kepler and TESS detect these tiny dips.

    Variables

    • δ — transit depth (fractional drop in brightness)
    • R_p, R_★ — planet and star radii

    Assumptions and limits

    • Planet fully inside the stellar disk (not grazing)
    • Uniform stellar disk — limb darkening makes central transits slightly deeper
    • Planet's night side emits no light at the observed wavelength

    For education only. These models are simplified and are not suitable for spacecraft navigation or safety-critical engineering. See our scientific accuracy policy.