How to measure the inclination of an exoplanet’s orbit

This animation illustrates how astronomers can measure the inclination of a planet’s orbit with respect to the rotation of the star. When a star rotates, light from the side approaching us appears shifted to bluer colours due to the Doppler effect, whereas light from the receding side is red-shifted. When a planet transits in front of the star it will block different parts of it, changing the shape of the spectral lines. If the planet transits in the same direction as the star’s rotation, the planet will first block the blue-shifted side of the star and then the red-shifted one, and vice versa if the planet orbits backwards. If the planet’s orbit is very inclined, the deformation of the spectral lines happen mostly at the centre of the lines rather than from side to side.