The Moon experiences extreme thermal conditions, cycling rapidly between intense heat and profound cold. Lunar surface temperature is not a single value but a wide range dependent entirely on sunlight exposure. These drastic conditions present significant challenges for human and robotic exploration. Understanding how cold the Moon gets requires looking beyond the basic day and night cycle to specific geographical features.
Defining the Far Side and the Dark Side
The idea of a “dark side of the Moon” is a widespread misconception suggesting one hemisphere is permanently cold and unilluminated. The Moon is tidally locked with Earth, meaning the same face, the near side, always points toward us. While there is a far side we never see from Earth, it receives the same amount of sunlight as the near side over a lunar month.
The true “dark side” is simply the hemisphere currently experiencing night. As the Moon rotates, both the near and far sides cycle through approximately 14 Earth days of intense sunlight followed by 14 Earth days of darkness. Therefore, temperature extremes are defined by whether the Sun is shining on a location, not by which side is facing Earth.
What Causes the Moon’s Extreme Temperature Swings
The scale of temperature variation on the Moon is a direct consequence of its physical environment. Unlike Earth, the Moon has virtually no atmosphere; it is surrounded by a near-total vacuum called an exosphere. Without a dense gaseous blanket, there is no mechanism to trap heat, insulate the surface, or distribute thermal energy.
When sunlight strikes the lunar surface, heat is absorbed directly, causing temperatures to climb rapidly. When the Sun sets, the absorbed heat immediately radiates back into space, leading to an equally rapid drop. This radiative cooling is exacerbated by the Moon’s slow rotation, resulting in a lunar day and night that each last about 14 Earth days.
Measured Temperatures During the Lunar Night
During the lunar night cycle, surface temperatures plummet to profoundly cold levels. Near the lunar equator, daytime temperatures can reach approximately 250 degrees Fahrenheit (121 degrees Celsius). Once night falls, these equatorial regions drop to an average of about -208 degrees Fahrenheit (-133 degrees Celsius).
The specific temperature varies depending on latitude and the composition of the lunar soil, known as regolith. Regolith is a poor conductor of heat, meaning temperature changes are largely confined to the uppermost layers of the surface. Even a few feet below the surface, temperatures stabilize considerably, demonstrating the insulating qualities of the lunar soil against these extremes.
Permanently Shadowed Regions and Deep Cold
The most extreme cold on the Moon is found within specific topographical features near the poles. Due to the Moon’s minimal axial tilt, the Sun always skims low across the horizon. This geometry creates deep, shadowed craters where direct sunlight never reaches the crater floor, regardless of the day-night cycle. These areas are known as Permanently Shadowed Regions (PSRs).
Within PSRs, temperatures act as natural cold traps. The Lunar Reconnaissance Orbiter’s Diviner instrument has measured temperatures in these regions falling below -410 degrees Fahrenheit (-246 degrees Celsius). In some spots, such as within the Hermite Crater, temperatures have been recorded as low as -424 degrees Fahrenheit (-253 degrees Celsius), making them among the coldest natural environments measured in the solar system. This extreme cold allows for the stable preservation of volatile materials, including water ice, which is a major focus for lunar exploration missions.