Temperatures on the moon are extreme, ranging from boiling hot to freezing cold depending on where the sun is shining. There is no significant atmosphere on the moon, so it cannot trap heat or insulate the surface.
The moon rotates on its axis in about 27 days. Daytime on one side of the moon lasts about 13 and a half days, followed by 13 and a half nights of darkness. When sunlight hits the moon's surface, the temperature can reach 260 degrees Fahrenheit (127 degrees Celsius). When the sun goes down, temperatures can dip to minus 280 F (minus 173 C). Temperatures change all across the moon, as both the near and far side experience sunlight every lunar year, or terrestrial month, due to lunar rotation.
The moon tilts on its axis about 1.54 degrees — much less than Earth's 23.44 degrees. This means the moon does not have seasons like Earth does. However, because of the tilt, there are places at the lunar poles that never see daylight.
The Diviner instrument on NASA's Lunar Reconnaissance Orbiter measured temperatures of minus 396 F (minus 238 C) in craters at the southern pole and minus 413 F (minus 247 C) in a crater at the northern pole.
"These super-cold brightness temperatures are, to our knowledge, among the lowest that have been measured anywhere in the solar system, including the surface of Pluto," David Paige, Diviner's principal investigator and a UCLA professor of planetary science, said in a 2009 statement. Since then, NASA's New Horizons mission set Pluto's temperature range at a comparable minus 400 to minus 360 F (minus 240 to minus 217 C).
Scientists suspected that water ice could exist in the moon's dark craters that are in permanent shadow. In 2010, a NASA radar aboard India's Chandrayaan-1 spacecraft detected water ice in more than 40 small craters at the moon's north pole. They hypothesized that over 1.3 trillion lbs. of water ice hid among the permanently darkened craters.
"After analyzing the data, our science team determined a strong indication of water ice, a finding which will give future missions a new target to further explore and exploit," Jason Crusan, program executive for the Mini-RF Program for NASA's Space Operations Mission Directorate in Washington, said in a statement.
Layers of insulation
Astronauts on the moon were protected from the extreme temperatures by their spacesuits. The suits had several layers of insulating material covered by a highly reflective outer layer. The suits also had internal heaters and cooling systems.
The moon has an iron-rich core with a radius of about 205 miles (330 km). The temperature in the core is probably about 2,420 to 2,600 F (1,327 to 1,427 C). The core heats an inner layer of molten mantle, but it's not hot enough to warm the surface of the moon. Because it is smaller than the Earth, the moon's interior temperatures don't climb as high.
"It's not as hot [as Earth's interior] because the moon is smaller — hence its internal pressure is also smaller," NASA planetary scientist Renee Webber said during an online chat hosted by NASA. "The temperatures are probably lower than those of Earth."
Additional reporting by Nola Taylor Redd, Space.com contributor.