Two independent detection methods reveal unseen planets. The transit method catches the tiny dimming of starlight as a planet crosses in front of its star. The radial velocity method catches the star's own wobble, as gravity from the orbiting planet tugs it around their shared center of mass, Doppler-shifting its spectrum.
Transit depth = (R_planet / R_star)²
RV semi-amplitude K = (2πG / P)^(1/3) · M_p·sin(i) / M★^(2/3)
- Planet radius — larger planets block more starlight, deepening the transit dip.
- Orbital distance — sets the orbital period via Kepler's third law and the RV amplitude.
- Inclination — near 90° means the orbit is edge-on and a transit is visible; lower values miss the transit entirely but RV still works.
- Transit / Radial velocity toggle — switches which detection signal is displayed: the dimming light curve, or the star's velocity wobble vector.
NASA's Kepler and TESS missions found thousands of worlds this way, and ground-based spectrographs like HARPS pioneered radial-velocity discoveries such as 51 Pegasi b.