Transit

15 chapters, each an animated explainer with its physics and sources. Every drawing says whether it is an illustration, a model from stored values, or real data, and by how much it is exaggerated. Only the transit chapter is something SetuHQ itself does.

Chapter 2 of 15 · SetuHQ does this

Transit

When a planet crosses its star, it blocks a little light. The dip's depth gives the planet's size relative to the star; its repetition gives the period. This is what SetuHQ does: its run found pi Men c's transits in TESS sector 1. Open SetuHQ's Transit case ›

Model from stored valuesPlanet: artist's impression ›
pi Men, a G0V-like star (6037 K, drawn in its blackbody colour) with pi Men c crossing it at impact parameter 0.5738. Below, a limb-darkened model light curve drawn from the stored radii, with SetuHQ's stored points for its lead dip overlaid as dots.

What shapes the dip

The depth is roughly (Rp/R★)². The star is brighter at its centre than its edge (limb darkening), so the bottom of the dip is rounded, not flat, and a central crossing dips deeper than k² (Mandel & Agol 2002; Claret 2017 coefficients for TESS). The four contact points set the total duration T14 and the flat-bottom duration T23 (Winn 2010).

QuantityValueFrom
Rp/R★ (k)0.0156exoplanet.eu Rp = 0.16719 RJ, R★ = 1.1 R☉ [calc]
k² (depth with no limb darkening)244 ppm[calc]
Model depth at the stored b267 ppmquadratic limb darkening u₁ = 0.333, u₂ = 0.228 (Claret 2017, 6037 K) [calc]
Model depth for a central crossing287 ppm[calc]
SetuHQ's fitted depth, lead dip294 ppmsetuhq run, limb-darkened fit, mid-transit depth (real data)
T14 / T233.07 h / 2.93 hWinn 2010 eqs. 14–15 from a/R★ = 13.10, b = 0.5738 [calc]; Huang 2018 publish 2.953 ± 0.047 h
StarG · ≈G0V · rgb(255, 244, 242)nearest row of Mamajek's sequence; blackbody colour from the CIE 1931 fit

The curve is a model drawn from stored values (small-planet approximation of Mandel & Agol 2002, circular orbit), not observed data. The dots are SetuHQ's own stored points for its lead dip. The orbit is not to scale; its tilt is set so the planet crosses at the stored impact parameter.

4,790 of the 8,049 planets with a stored distance in exoplanet.eu were found by transit (the first method listed). Show them on the Galaxy map ›

peak 1,450 (2016)

19882026

Planets found by transit per year, 1988–2026: 4,790 in all; the most in one year was 1,450 in 2016. Source: exoplanet.eu, fetched 2026-10-18.
Planets in this chapterpi Men c ›TRAPPIST-1 b ›WASP-39 b ›
Sources

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