Exoplanets and the Rossiter-McLaughlin Effect

A transiting planet eclipses part of the rotating stellar surface, thereby producing an anomalous Doppler shift of the stellar spectrum. Here I review how this ``Rossiter-McLaughlin Effect'' can be used to characterize exoplanetary systems. In particular, one can measure the angle on the sky between the orbital axis and the stellar rotation axis. This may help to discriminate among migration theories. Measurements have been made for 4 exoplanets, and in all cases the spin and orbital axes are fairly well-aligned. In the future, the Rossiter-McLaughlin effect may also be important as an alternative means of probing exoplanetary atmospheres, and for confirming the transits of objects identified by the satellite missions Corot and Kepler.