Uranus’s obliquity is 98°. An obliquity value greater than 90° indicates that the planet rotates in a clockwise direction when seen from above its orbital plane. Venus, Pluto, Pluto’s moon Charon, and Neptune’s moon Triton are the only other major bodies known to behave this way. Uranus’s high obliquity causes its seasons to be extreme, with each polar region alternately experiencing 42 years of continual sunshine followed by 42 years of total darkness. Averaged over an entire orbit, the poles receive more sunlight than the equator—a situation quite different from that of any other planet. Why does Uranus have an obliquity so different from those of the other planets? One possible explanation is that the planet was “knocked over” by the impact of one huge or several large planetesimals near the end of its accretion phase.