On July 20, 1969, astronauts Neil Armstrong and Buzz Aldrin landed on the moon while fellow astronaut Michael Collins orbited in a command module. Conspiracy theories denying the moon landing soon started.

For authoritative Web sites debunking these conspiracy theories, see:

Robert Braeunig explains why stars are not visible in photographs taken on the moon:

The answer is very simple: they are too faint. The Apollo photos are of brightly lit objects on the surface of the Moon, for which fast [camera] exposure settings were required. The fast exposures simply did not allow enough starlight into the camera to record an image on the film. For the same reason, images of the Earth taken from orbit also lack stars. The stars are there; they just don’t appear in the pictures.

Redzero talks about the almost 400 kg. of moon rocks the astronauts brought back:

We know for certain that they came from the moon. 100% certain. They are like nothing else on Earth and they couldn’t have been constructed artificially because they bear the evidence of billions of years exposure to a vacuum, high energy cosmic rays, tiny asteroids and virtually no water. Nothing on Earth could replicate this, either naturally or man-made.

Phil Plait explains why the lunar landing module did not produce any flames when it took off from the moon:

There is actually a simple reason why you cannot see the flame from the lander when it took off. The fuels they used produced no visible flame! The lander used a mix of hydrazine and dinitrogen tetroxide (an oxidizer). These two chemicals ignite upon contact and produce a product that is transparent.

NASA recently stated it is “disappointed that conspiracy theorists ignore basic science principles to diminish arguably the greatest feat in the history of human exploration. It insults the dedication and the sacrifices made by hundreds of thousands of people who were a part of the Mercury, Gemini and Apollo programs.”