Lunar Reconnaissance Orbiter Spies Movement of Shadows Near the Moon’s South Pole

At the Moon’s North and South Poles, the Sun is never more than 1.5° above or below the horizon. The resulting pattern of daylight and shadows is unlike anywhere else on the Moon — or the Earth. After zooming in on a small lunar highland area near the South Pole, this visualization recreates the illumination conditions there over a period of two lunar days, equal to two months on Earth. This close to the pole, the Sun doesn’t rise and set. Instead, as the Moon rotates on its axis, the Sun skims the horizon, traveling a full 360 degrees around the terrain. Mountains as far as 75 miles (120 kilometers) away cast shadows across the landscape. With the Sun at such a low angle, it can never reach the floors of some deep craters. Places the Sun never reaches are known as permanently shadowed regions. They are the locations of some of the coldest spots in the solar system, and because of that, they trap volatile chemicals, including water ice, that would immediately sublimate (transform directly from a solid to a gas) in the harsh, airless sunshine that falls in most other places on the Moon.

The Sun appears to travel in a circle at the Earth’s poles, too, but it also travels through a range of altitudes. From spring equinox to summer solstice, for example, the Sun is climbing higher in the sky, reaching an altitude of 23.4°. It only hugs the horizon for a few days around the equinoxes. At the Moon’s poles, the Sun is always near the horizon, and the shadows are perpetually long, sweeping across the surface with the changing solar azimuth.