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Our friends in STARBASE at Robbins Air Force Base, Georgia, asked about the Apollo missions that landed on the moon. They wondered what protected astronauts from meteoroids while they were on the moon and why the flag appears to be waving in photos the astronauts took even when there is no wind there.
Meteoroids are mostly tiny rocks and dust that travel through space. Over billions of years, every spot on the moon has been struck by them many times. In fact, much of the dust that covers the surface of the moon was formed as rocks were slowly worn down by repeatedly being hit by these particles.
We know the mountains on the moon are smooth, but before the space program, many people believed they were jagged. They knew that, unlike Earth, there was no wind or water that would gradually make these sharp features more rounded. But now we understand that these meteoroids eat away at the mountains, just as wind or water would, although much more slowly.
Because Earth is a larger target and has stronger gravity to attract more space debris, it is hit by far more of these particles than the moon is. On the ground, we are protected by the atmosphere, which we rely on for so much. This blanket of air slows down the material that slams into it, keeping us safe. But the moon has no atmosphere, so its surface is hit directly. The meteoroids travel at such high speed, that if one of them hit an unprotected person there, it could be disastrous.
The space suits the astronauts wore on the moon were designed to protect them from the harsh conditions there. These suits were like human-sized spacecraft, providing everything a person needed to work comfortably for more than 7 hours. They were made of many layers, and the outer ones were specially designed to prevent an impact from penetrating this protective cocoon. The helmets also were made of special materials to protect the astronauts. Like bulletproof vests, the space suits would absorb the energy of high speed impacts.
Just as the absence of an atmosphere made it important to find a way to shield the astronauts from meteoroids racing through space, it presented engineers with another challenge, although this one was easier to solve. On each of the missions that landed, astronauts erected an American flag. Of course, engineers knew the flag would hang limp in the airless environment, but they wanted it outstretched to display the stars and stripes. So in addition to the vertical pole that supported the side of the flag, they included a horizontal arm along the top of the flag to hold it out. Sometimes the astronauts did not fully extend that arm, so the flag would not be stretched flat. That would leave some ripples in the fabric, making the flag appear in photographs as if it were waving in the breeze, even when it was perfectly motionless. In fact, if you ever saw video of the flags when the astronauts weren't touching them, you would see that they were completely still.
As the astronauts took off from the moon in their lunar module, the rocket engine's exhaust blowing across the surface sometimes made the flag wave briefly or even, in the case of Apollo 11, fall over. Later missions placed the flag farther from the spacecraft.
The photos from the Apollo missions are a wonderful record of one of humankind's greatest adventures. Enjoy pictures of space-suited astronauts on the moon, the flags they planted, and other items they used and left behind there.