We monitored the Doppler shift of the G0V star TrES-2 throughout a transit of its giant planet .
The anomalous Doppler shift due to stellar rotation ( the Rossiter-McLaughlin effect ) is discernible in the data , with a signal-to-noise ratio of 2.9 , even though the star is a slow rotator .
By modeling this effect we find that the planet ’ s trajectory across the face of the star is tilted by -9 \pm 12 deg relative to the projected stellar equator .
With 98 % confidence , the orbit is prograde .