MOSCOW – The surface of the Moon can heat up to 127 degrees Celsius during the day and cool down to minus 173 degrees at night, said Yevgeny Burmistrov, an astronomy expert at the Perm National Research Polytechnic University on Monday, the International Moon Day.

"The reason for such sharp fluctuations is the absence of an atmosphere that would moderate heating by solar rays and retain heat at night," Burmistrov said, adding that the Moon's deep craters remain in perpetual shadow, so temperatures there can drop to minus 240 degrees, among the lowest in the solar system.

Burmistrov also noted that due to internal cooling, the Moon's diameter has decreased by approximately 50 meters over the past few hundred million years. The process is accompanied by seismic activity, which could pose risks to spacecraft and potential lunar bases.

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International Moon Day is observed annually on July 20 since 2021. It marks the anniversary of the first landing by humans on the Moon during the Apollo 11 lunar mission in 1969.