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How much do you know about the Moon landings?

Most people can recite the phrase, "One small step for man, one giant leap for mankind", but other aspects of NASA's Apollo missions aren't common knowledge.

Strangely, every astronaut since the first Apollo 11 Moon landings in 1969 has reported seeing the mysterious flashes - whether their eyes are open or not.

On the Science Channel's show Nasa's Unexplained Files, it was explained: "Several of the Apollo astronauts reported seeing something strange as they approached the Moon."

One astronaut, Alan Bean, said: "I saw a flash and I thought 'did I really see a flash?"

(Image: REUTERS/NASA)

Another, Charles Duke, explained: "I'm having these light flashes. I'm seeing this, like, light flashing in my eyeballs.

"It was like fireworks in your eyeballs. It was spectacular."

Strangely, the men were seeing the flashes when their eyes were open and when they were closed.

On Moon missions, the lights were reported as being white.

On other missions, different coloured lights - such as blue or yellow - were observed.

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More worryingly, the astronauts continued to see the flashes when they returned home from space under various light conditions.

So what is it?

Scientists believed that the strange flashes were being caused by cosmic rays hitting the astronauts.

Cosmic rays are defined as "a highly energetic atomic nucleus or other particle travelling through space at a speed approaching that of light."

Defense Analyst Nick Pope told the show that the lights were caused by "the interaction of radiation with the brain - the optic nerve."

(Image: Getty)

Engineers designed an experiment to test whether cosmic rays were causing astronauts to see the flashing lights - a helmet-like black box that the men and women could put over their heads which would detect cosmic rays.

Astronaut Charles Duke wore the helmet on a mission, closed his eyes and started to describe the light flashes he was seeing to the team.

Charles described seeing 'clusters' of 'white streaks' at the same time as the helmet recorded cosmic rays passing through the helmet to his head.

And so NASA solved the mystery of the mysterious 'flashing lights'.

It's not the only weird thing that's been spotted from space.

Earlier this week a video purportedly from the International Space Station captured a UFO hurtling over Earth at lightning speed.

Then, the feed mysteriously cut out.

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YouTube user ColdPyro had shared the clip, which showed a silvery dot appearing from nowhere about six seconds into the footage.

Within moments the feed has been cut and the ISS testboard appears, with the message: "Please stand by.