Neptune

The tilt of Neptune's magnetic field to its rotation axis and the field's offset from Neptune's center cause fluctuations of its magnetic field that are associated with the rotation of Neptune's interior. From measurements of these fluctuations by Voyager 2, the rotation period of Neptune's interior of 16 hours, seven minutes was determined; this was the first reliable determination of Neptune's rotation period. The 12-21 hour rotation periods found for the atmospheric features observed by Voyager 2 differ from the above value because of winds.