How this calculator works
A transit blocks a fraction of a uniformly bright star equal to the planet-to-star area ratio. Radial velocity uses a Keplerian stellar reflex semi-amplitude, retaining both masses, inclination and eccentricity. Astrometry uses the stellar barycentric semi-major axis divided by distance in the small-angle limit. The wavelength outputs show a first-order radial Doppler shift at plus or minus the velocity semi-amplitude, not a full eccentric-orbit spectrum.
Formula
Transit depth = (Rp/Rstar)². K = (2 pi G/P)^(1/3) Mp sin(i)/[(Mstar+Mp)^(2/3) sqrt(1-e²)]. Astrometric angle = a Mp/[(Mstar+Mp)d] radians. delta-lambda/lambda approximately vr/c.
Worked example
A planet of radius 10 units crossing a star of radius 100 units gives a 1% transit depth. A 4% depth across a 200 m model star implies planet radius 40 m.
Advertisement
Frequently asked questions
Does a transit give planet mass?
No. It primarily constrains radius relative to stellar radius; velocity or other data are needed for mass.
Why does inclination matter?
Radial velocity measures only the line-of-sight component. A face-on orbit has essentially no radial signal.
Can these calculations confirm a discovery?
No. Stellar activity, eclipsing companions, limb darkening, noise and orbital fitting must be assessed with actual observations.