The moon landing conspiracy involves the belief that American astronauts (Neil Armstrong and Buzz Aldrin) never landed on the moon in 1969. Instead, conspiracy theorists believe that the men only acted out their moon landing on a set somewhere.
The main reason some people don't think the moon landings happened is an ideological distrust in authority. These people have lost faith in the institutions they were taught to trust. Conspiracy theorists extrapolate that they have the facts to back up their claims of government malfeasance. First, they assert that there are no stars in any of the moon landing photographs.
Conspiracy theorists believe that set designers simply "forgot" to include the stars. The reality is a little less exciting: the immense light of the sun hitting the surface of the moon probably blocked out the stars from human vision. Next, conspiracy theorists argue that there is a stray rock in the picture marked with the letter 'C.' Scientists claim that the 'C' may have just been a photographic anomaly, possibly a stray hair or a piece of string.
Conspiracy theorists also argue that the shadows of the astronauts seem to be of different lengths, even when they are standing side by side. Scientists debunk this claim by arguing that the scientists were standing on hilly landscapes, and such irregular terrain is notorious for playing havoc with shadow lengths.
Not to be deterred, conspiracy theorists put forth the hypothesis that the flag in the moon landing picture appears to be flapping. They argue that since there is no air on the moon, it would be impossible for a breeze to disturb the flag in this way. However, scientists explain the "flapping" by pointing out that it was caused by the astronauts' rough handling of the flag as they planted it on the moon's surface.
Last, but not least, conspiracy theorists claim that NASA duplicated the astronaut moon walk by using wires and camera manipulations to make it appear as if the astronauts were on the moon. Meanwhile, scientists point out that the evidence does not support this claim. If the astronauts were on earth, clouds of dust would have formed as they disturbed the surface of the ground in the act of walking. In the NASA photographs, there is no cloud of dust that accompanies the astronauts' movements along the moon's surface.