Sidereal Rotation Period of Uranus

Uranus's clouds are so bland that no telescope could ever clock the rotation; the 17.24-hour figure comes from Voyager 2's nine days of listening to radio bursts tied to the magnetic field, and it has never been checked by a second spacecraft. Formally the NSSDC lists it as −17.24 h: with the spin axis tipped 98°, past the perpendicular, the rotation is technically retrograde — a bookkeeping consequence of the tilt rather than a separate oddity.

The field doing the broadcasting turned out to be its own surprise: offset from the planet's centre by a third of the radius and inclined 59° to the spin axis, a lopsided magnet whose origin is still debated — possibly generated in a thin shell of ionic water rather than a deep core. Because the field is the only handle on the interior's rotation, the 17.24-hour day inherits every uncertainty about the field itself; models of the interior treat its last digits gently.