Astronomers Determine the Length of Day of an Exoplanet

The Bad Astronomer writes: "Astronomers have just announced that the exoplanet Beta Pic b — a 10-Jupiter-mass world 60 light years away — rotates in about 8 hours. Using a high-resolution spectrometer and exploiting the Doppler shift of light seen as the planet spins, they measured its rotation velocity as 28,000 mph. Making reasonable assumptions about the planet's size, that gives the length of its day. This is the first time such a measurement has been achieved for an exoplanet."