While the common wisdom that the moon lacks an atmosphere has been part of general knowledge for years, a NASA document released in January 2014 indicates that the moon does have an atmosphere with gases like potassium and sodium which do not appear in the atmosphere of Venus, Mars or Earth. The atmosphere on the moon has much less gas in it; on Earth, the sea-level atmosphere has 10 quintillion molecules per cubic centimeter, while that same cubic centimeter only has 1 million molecules on the moon. So while the lunar atmosphere is quite thin, it nevertheless exists.
The Apollo 17 mission used the Lunar Atmospheric Composition Experiment on the lunar surface to analyze what the air was actually like on the moon. This study found minuscule amounts of several different types of molecules and atoms, such as argon, helium and possibly ammonia, carbon dioxide, neon and methane. Researchers on Earth using telescopes designed to block lunar light have captured images of the glow that the potassium and sodium atoms create when they receive energy from the sun. These gases likely came from solar wind particles and high-energy photons, as well as surface material evaporation, material grabbed from meteoroid and comet impact, and gas come from the interior of the moon.