HAT-P-6b is a transiting extrasolar planet discovered by Noyes et al. on October 15, 2007. It is located approximately 910 light-years away in the constellation of Andromeda, orbiting the star HAT-P-6. This hot Jupiter planet orbits with a semi-major axis of about 0.05 AU, and takes 92 hours, 28 minutes, 17 seconds to orbit the star. It has true mass of 5.7% greater than Jupiter and a radius 33% greater than Jupiter, corresponding to a density of 0.583 g/cm₃, which is less than water.

The planet HAT-P-6b is named Nachtwacht. The name was selected in the NameExoWorlds campaign by the Netherlands, during the 100th anniversary of the IAU, after Rembrandt's painting The Night Watch.

The sky projected angle between stellar and orbital axis is roughly 166°, making it one of the few planets that is in a retrograde orbit around its parent star. Observations made by Spitzer Space Telescope shows that the planet atmosphere has a weak temperature inversion, or no inversion at all, depending on how strong is the stellar chromospheric activity.

Media related to HAT-P-6 b at Wikimedia Commons

• "HAT-P-6 b". Exoplanets. Archived from the original on 2012-04-01. Retrieved 2010-01-20.