Moon Essentials: Seasons

The lunar South Pole will be the target of both robotic and human exploration missions in the coming years, and the timing of their arrival will be driven by, among other things, the seasonal ebb and flow of available sunlight there. Both the Earth and the Moon experience seasons caused by their axial tilt relative to the Sun. But while the Earth is tilted 23.5°, the tilt of the Moon is a mere 1.5°, making its seasonal changes quite subtle. As on Earth, the largest effect is at the poles.

In this visualization, the monthly rotation of the Moon has been frozen at full moon in order to highlight the small difference in axial tilt at South Pole summer and winter. The left half of the frame shows the western hemisphere of the Moon, including the Orientale basin on the terminator (day-night line). Only the lit half of this view is visible from Earth. The right half of the frame is an overhead view of the South Pole region, with the perfectly bowl-shaped Shackleton crater in the center. The near side (the side facing Earth) is up in this view.

The complete seasonal cycle on the Moon is its draconic year of about 346.6 Earth days. This is shorter than an Earth year because the Moon's orbit plane rotates once every 18.6 years, and its axis precesses at the same rate, bringing each season around somewhat faster than it would arrive otherwise.