Astronomers who study the moon are looking forward to the night of Jan. 31, which will feature what is being called a super blue blood moon. But the scientists are looking forward to the lunar eclipse that night, which offers an unusual chance to study the moon’s surface.

The surface of the moon is covered in lunar regolith — a sticky mixture of dust, soil, small and broken loose rocks, and other such material — which is estimated to be anywhere between 4-5 meters and 15 meters deep, depending on where you look on the moon. The crewed missions to the moon revealed the lunar dust to be very abrasive, and therefore detrimental to space suits and electronics.

And since NASA is considering crewed missions to Earth’s only natural satellite once again, it becomes important to better understand lunar regolith, to better plan for future missions.

Since the moon has no atmosphere of its own, there are large differences of temperature between the lunar day and night, more extreme than the hottest and the coldest places on Earth. At the peak of daytime on the moon, it is about 100 degrees Celsius, hot enough to boil water just by leaving it out. During the night, on the other hand, it can fall to 173 degrees Celsius below zero.

But unlike the day-and-night cycle on Earth, which takes 24 hours, the same cycle takes about 29.5 Earth days on the moon. But during a lunar eclipse, with our planet blocking off direct sunlight that would otherwise fall on the moon’s surface, the temperature variation is much faster.

“During a lunar eclipse, the temperature swing is so dramatic that it’s as if the surface of the Moon goes from being in an oven to being in a freezer in just a few hours,” Noah Petro, deputy project scientist for NASA’s Lunar Reconnaissance Orbiter (LRO) at Goddard Space Flight Center in Greenbelt, Maryland, said in a statement Tuesday.

lunar eclipse diagram When a lunar eclipse occurs, the Earth moves between the sun and moon and casts a shadow on the moon. Photo: NASA

During the Jan. 31 lunar eclipse, astronomers will point thermal cameras at the moon, using the Haleakala Observatory on the island of Maui in Hawaii, NASA said.

“The whole character of the Moon changes when we observe with a thermal camera during an eclipse. In the dark, many familiar craters and other features can’t be seen, and the normally non-descript areas around some craters start to 'glow,' because the rocks there are still warm,” Paul Hayne of the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder, explained in the statement.

The size of the rocks, their physical properties and their chemical composition all play a role in how fast or slow their surfaces lose heat. The short-term changes during the eclipse, observed through thermal cameras, will allow researchers to gather information about the behavior of the very top layer of lunar regolith.

Thanks to data collected by LRO’s Diviner instrument since June 2009, scientists already know a lot about how temperatures change between day and night, and over seasons, on the moon. This long-term information helps astronomers understand the larger features and bulk properties of the top few inches of the regolith.

The blood part of the super blue blood moon is actually related to the lunar eclipse. The only light reflected off the moon’s surface during an eclipse is that which reaches it through Earth’s atmosphere. Particles in the atmosphere scatter and bend light, giving it a reddish hue. So the moon appears reddish in color, giving rise to a blood moon.