4.5 Interpreting the radial velocity curve
From the radial velocity curve you can work out the orbital period of a planet – the time it takes to complete an orbit. As you have already learned, the time taken for the Earth to complete an orbit is one year. The maximum radial velocity tells you how fast a star is moving in its orbit around the centre of mass. You can read that off the radial velocity curve – it’s the value at the top of the peak. If you know the mass of the star, combining this with the measured orbital speed allows you to work out the mass of the planet.