How do we know that we went to the Moon?

But even today, 50 years later, people discuss conspiracy claims online, on television programmes and around the dinner table.

Moon fact: With a powerful amateur telescope you can see the Apollo landing sites and, if you look at the photos from the Lunar Reconnaissance Orbiter, you can spot the remnants of the Apollo missions yourself.

Were the Moon landings faked?

If you find yourself in a debate questioning whether humankind first stepped on the Moon on 20 July 1969 the chances are that you are woefully underprepared. Most people take it as gospel that the US government, Nasa, the 12 astronauts in total who have walked on the Moon and the 400,000 people involved in the Apollo programme would have neither the will nor the way to fake one of humanity’s greatest ever achievements.

But there are those who think the landings were a hoax. They claim the US government faked Apollo 11 and later missions either to deal a crucial blow to the USSR in the Space Race, or to boost Nasa funding or to divert attention away from the Vietnam war. The argument for any of these viewpoints rests on finding evidence that the landings were faked.

And more often than not, people point out peculiarities in specific images or videos to deal the critical blow. If someone uses these oddities as evidence, what do you say? Here are the most common arguments that support this view, and why each of them is wrong.

Photographic evidence

One of the most popular conspiracy arguments is that there are never any stars in Apollo photos. Free from Earth’s light pollution and hazy atmosphere, you would expect to see thousands of stars in all the astronauts’ images. Unfortunately, this argument rests on the photos being snapped during the lunar night. All manned missions to the Moon took place in sunny daytime. This meant starlight lost the battle against the very bright surface of the Moon, too dim to show up in photos.

Another common argument is that the crosshairs that appear in many Apollo images sometimes appear to be behind objects in the photos. If the images were real this would be impossible, suggesting someone painted them on. But testing here on Earth has shown that the brightly lit objects make the crosshairs appear fainter. When these images are copied or scanned some of this detail is lost completely, giving the effect that the crosshair is behind the object in certain shots.

Others point to an oddity in a photo of a Moon rock taken during the Apollo 16 mission. There appears to be a C written on it, like a lettered movie prop. Again, analysing the original photo there is no anomaly ­– the ‘C’ isn’t there. Most likely it was a piece of hair or thread introduced during copying.

A more subtle argument that the landings were faked is based on various misunderstandings of Nasa equipment and lunar physics. A well-known example is the American flag that Neil Armstrong and Buzz Aldrin placed on the Moon. It appears to flutter in the wind in some photos. How could this happen when the Moon has no wind?

In fact, it isn’t fluttering at all. A horizontal rod at the top of the pole holds the flag unfurled. This makes it look like the wind is stopping it from hanging down. And there is a fluttering effect because the weak gravity on the Moon is not strong enough to uncrumple the flag. After a little waving while the astronauts planted the flags into the Moon’s surface, they have remained still ever since.

Fried by radiation

Perhaps the most convincing argument that the landings were faked has to do with something called the Van Allen belts. These are two giant doughnut-shaped belts surrounding the Earth. They are made of highly energetic charged particles from the solar wind. Some people believe humans couldn’t have passed through these belts without being exposed to lethal doses of radiation.

This was a genuine concern before the Apollo missions. And it is the reason scientists behind Apollo 11 made sure they protected the astronauts as best they could. They insulated the spacecraft from radiation with an aluminium shell. And they chose a trajectory from the Earth to the Moon which minimised the amount of time spent in the Van Allen belts.

Readings from the nine Apollo missions that reached the Moon showed the astronauts’ average radiation exposure was 0.46 radiation-absorbed dose (rad). This proved Nasa was right to shield the astronauts from radiation. Though it’s less than that experienced by some nuclear energy workers, 0.46 rad is around 10 times more than the radiation exposure of medical professionals who routinely work with x-ray and radiotherapy machines.

Proof we walked on the Moon

Of course, until we return to the Moon there will always be anomalies and oddities in the records that can spark new claims that the Moon landings were faked. But it is the sheer size and variety of this record that proves every one of these claims to be false.

From the Apollo Moon missions, there are 8,400 publicly available photos, thousands of hours of video footage, a mountain of scientific data, and full transcripts and audio recordings of all air-to-ground conversations. We even have 382 kilograms of Moon rock that Apollo astronauts brought back to Earth. These rocks have been independently verified as lunar by laboratories around the world, ruling out a US conspiracy.

If this is not enough to convince the most-hardened sceptic, Nasa’s Lunar Reconnaissance Orbiter (LRO) might sway them. Today, LRO takes high resolution pictures of the lunar surface from a low orbit. During its mission, it has captured the landing sites and the abandoned descent modules and rovers from the Apollo missions. And its resolution is so good it has picked up the dark squiggly paths that the astronaut’s footprints made. Spacecraft from China, India and Japan have also spotted these landing sites, providing further independent verification of the landings.

A final nail in the coffin of the Moon hoax theories is a simple instrument installed 50 years ago by Apollo 11. During their day on the Moon, Armstrong and Aldrin planted a lunar laser ranging retroreflector array on the surface. It’s still operational today, and allows us to reflect lasers off of it and measure the distance to the Moon down to the centimetre. We simply couldn’t do this if we hadn’t visited the Moon.