| Extrasolarplanet: | yes |
| HAT-P-6b / Nachtwacht | |
| Discoverer: | Noyes et al. |
| Discovered: | October 15, 2007 |
| Discovery Method: | transit |
| Apsis: | astron |
| Semimajor: | AU |
| Inclination: | ° |
| Period: | d |
| Star: | HAT-P-6 |
| Mean Radius: | 1.33 ± 0.06 |
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.[1] [2]
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.