Of all the concerns NASA astronauts may have had during six successful missions to the Moon between 1969 and 1972, weather conditions at their destination were not among them. They expected to experience cloudless, windless landings and Moon walks, and that's what they got, every time. In fact, that is what any visitor to the Moon would find at any time. There simply is no weather on the Moon.

Weather requires the presence of an atmosphere, like the blanket of gas molecules that surrounds Earth. The Moon has no atmosphere because, at one-quarter the diameter and a bit more than half the density of Earth, the Moon's gravity is about one-sixth the gravity of Earth. Gravity is a force that exists between any two objects that have mass. The more massive an object and the closer it is to another object, the greater the gravitational force it exerts on that object. Earth exerts a gravitational force on gas molecules in the atmosphere, including nitrogen, oxygen, water vapor, ozone, and carbon dioxide, just as it does on much more massive objects on its surface. The gravitational force the Moon exerts, however, wasn't strong enough to retain any gases that might have surrounded it shortly after it formed. Today, the Moon has little if any gas surrounding it, and thus no wind or weather.

The fact that the Moon has no weather doesn't mean that environmental differences don't exist on its surface. In fact, temperatures on the surface of the Moon swing wildly from one extreme to the other, from an average of -184°C (-300°F) in the shade to an average of 101°C (214°F) in the sun, precisely because of the lack of atmosphere there. On Earth, greenhouse gases, including water vapor, methane, ozone, nitrous oxide, and carbon dioxide, absorb and hold energy from the Sun that has been radiated by Earth's surface. By doing so, they keep Earth's surface temperature within a range that supports life.

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