It was 44 years ago, on July 20/21, 1969, that two men — Neil Armstrong and Buzz Aldrin — made history by becoming the first two humans to set foot on the Moon. Regardless of the excitement and fervor that accomplishment caused at the time, in the years since there have been plenty of people who have tried to cast doubt over the achievement and they've used various arguments to support their claim that it was all a hoax.
#1: The astronauts would have died from radiation exposure
This is probably the most common 'Moon hoax' claim that I've seen: The astronauts would not have been able to survive the trip because they would receive a lethal dose of radiation, both from passing through the Van Allen radiation belts and from being beyond Earth's magnetic field and on the Moon's surface.
The truth is, for their entire trip to the Moon and back, the astronauts only received a dose equal to around one-tenth of one per cent of the radiation needed for a lethal dose (their total exposure was roughly 11 millisieverts and a lethal dose is at 8,000 millisieverts).
The reason for this is that the harmful effects from radiation are based on strength of the radiation and the time of exposure. You'd need to spend nearly four months inside the Van Allen belts to accumulate a lethal dose. The astronauts passed through them in roughly one hour. As for their time spent beyond Earth's magnetic field, where they were exposed to cosmic radiation, as I discussed back at the end of May, an astronaut could make a one-way trip to Mars and not receive a dose that exceeds NASA's lifetime limits (and those don't even come close to lethal levels).
#2: You can't see the stars in photos of the Moon
Here on Earth, when there's a black sky, we see stars. The photos taken on the Moon show the astronauts, lander and terrain with a black sky, but no stars. So, they must have been filming on a sound-stage and just used a black backdrop.
When the astronauts were out taking pictures, it was full daylight on their side of the Moon. There's only an extremely thin atmosphere on the moon — not enough to block out the stars during the day — so the sky still appears black. It also means that the sunlight is very strong at the Moon's surface. If the astronauts aimed a camera at the sky and let it sit there and take a long-exposure picture, you would, indeed, see the stars. However, with astronauts taking pictures of each other, in their bright white suits (designed to reflect as much sunlight as possible to keep the suits from overheating), the camera couldn't get a good, crisp picture of the astronaut and still have the right exposure to pick up the much fainter stars in the background. Even taking pictures of the surrounding lunar landscape would have too much reflection from the surface to let the camera get a good exposure on both the landscape and the stars.
#3: Astronauts can be clearly seen even though they should be in shadow
There's a famous picture of Buzz Aldrin on the surface of the Moon, where he's casting his shadow in front of him. With the Sun behind him, some think that the entire front of his spacesuit should have been in shadow, so it's clear to them that there's a second light source, and thus they weren't really on the Moon when the photo was taken.
However, this has to do with how bright the sunlight is and how reflective the surface of the Moon is. The Sun is, indeed, behind Aldrin, but there's so much light being reflected from the bright surface of the lunar landscape that it's still fully illuminating the front of Aldrin's suit.
The same thing goes for another image where an astronaut is standing in the shadow of the lunar lander. The surface of the Moon is reflecting so much light onto the astronaut and the astronaut's suit is such a bright-white, that it's reflecting enough to be clearly visible while in the shadow.
#4: Cross-hairs in the Moon pictures get 'cut off'
There are dark cross-hairs in the images from the Moon, and in some pictures, part of the cross-hairs are missing. Some have used this to say that these pictures are doctored, or that the cross-hairs were actually painted on the backdrop of a sound-stage, and that the 'film-makers' accidentally put objects in front of them.
These 'black' cross-hairs are actually physically etched into a glass plate — called the Reseau plate — just in front of the film, and they aren't actually black, they're clear just like the rest of the plate. They only show up dark against the background because the light passes through those parts of the plate differently than the rest of the plate. A crack in the plate would achieve roughly the same effect.
The reason why some of these etched lines are 'missing' from the photographs is, again, because of the limitations of photography at the time. The emulsion the pictures were developed in couldn't differentiate between the dark line and the bright white on either side, so that part of the crosshair is 'washed out'. Scans taken much more recently are able to pick up the difference between the light and the dark, so the crosshairs show up.
#5: The shadows on the Moon go in different directions
In some pictures, the shadows from different objects in the field of view are pointing in different directions. This is another of the 'more than one light source' arguments.
Shadows from different objects pointing in different directions is is not only due to perspective, but also due to different angles of the terrain.
William Ian Goddard put together a great test on his website:
The lunar lander and the rocks have shadows that point in different directions, but the lander is on flat ground and the rocks are on a small rise. As shown in the model, this makes them have different shadow directions from the same light source. The pen in the model picture shows that even its shadow is pointing in a slightly different direction, being closer to the camera (thus demonstrating the 'perspective' part).
#6: The Moon has no air, but the U.S. flag flutters in the breeze
Well, there actually is air on the Moon. It's just extremely thin. Earth's atmospheric pressure at sea level is roughly 100,000 Pascals. The lunar atmospheric surface pressure reaches a maximum of about one ten-millionth of a Pascal during the daytime (and it's even lower at night). However, it's true that's not going to make a flag flutter.
The flag wasn't fluttering because there was a breeze. Not only had the astronauts just unrolled it, but they were also twisting the flag pole back and forth to dig it deeper into the lunar soil, so that it wouldn't fall over.
So, with all of that angular momentum transferred to the flag — from unrolling it and from twisting the flag pole — no breeze was needed for it to flutter. In fact, because there's not enough atmosphere to push against the flag, it could keep fluttering for a very long time if the astronauts let it.
#7: Pictures with the same background but different foreground
There are photographs taken on the Moon that show the same view of mountains in the distance, but one shows the lander in the foreground and the other doesn't. To those that believe the Moon landing was a hoax, this means that the images are faked.
However, the only thing that's happened there is that the astronaut has moved the camera some ways off to the side. This kept the mountains in the view, but took the lander out of the field of view of the camera. The reason the mountains still look identical is because they are extremely far away. Moving off to one side by a few tens of metres isn't going to change the perspective enough to make the mountains look different.
The reason why it's hard to see that the mountains are that far away is because, here on Earth, the atmosphere helps us gauge how far away something is by making more distant objects appear fuzzy or hazy. On the Moon, with its extremely thin atmosphere, that doesn't happen.
For an example of how hard it is to gauge distance, check out this video of the astronauts from Apollo 16 walking towards a boulder.
The astronauts are walking for an awful long time before they get to the boulder, which looked to be only short distance away at the start of the video.
#8: No flames appeared from the launch of the lunar lander back into space
When the lunar lander launches back into orbit, there's no flame visible from the bottom of the lander.
This one is fairly simple: the rocket reaction that launched the lunar lander back into orbit was one that doesn't produce a visible flame.
Even if it was a reaction that did produce flames, like we see here on Earth when a rocket propels something into orbit, the flames are visible because of Earth's atmosphere. There's not enough air on the Moon and no oxygen at all, so the rocket on the bottom of the lander would provide the thrust without the flames.
#9: We have plenty of telescopes, but none have taken pictures of the landing sites on the Moon
With all of our telescopes here on Earth and even the incredibly powerful Hubble Space Telescope, noone has taken pictures with any of them of the landing sites on the Moon. That must mean that they're not really there.
It is true that we haven't aimed our most powerful telescopes at the landing sites on the Moon and it's also true that if we did, we wouldn't see anything. That's not because the Moon landing didn't happen. It's because of the limitations of telescopes, based on size and distance.
The Hubble Space Telescope can take amazing images of objects extremely far away, but that's because those distant objects are immense. Just think of the images the telescope took of Pluto and its newest moons. Even though they're much closer than those distant objects Hubble snaps pictures of, they are much smaller (between 10 and 30 km wide), and Hubble can barely see them.
Even though the Moon is much closer than Pluto, Hubble's most sensitive camera still can't resolve objects as small as those left on the Moon. According to HubbleSite.org, an object four metres across would still be too small to see properly. It would just show up as a dot.
We do have orbiters around the Moon that have taken images of the landing sites, though. These images clearly show the landers, equipment and tracks made by the astronauts and their moon-buggies.
#10: There's no way to prove we went to the moon and without proof I won't believe it
With some time and the right set of equipment, you can actually prove that there are man-made objects on the Moon.
I'll let the cast from The Big Bang Theory take this one:
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