How does the Flag Wave on the Moon?
Published on Aug 13, 2006 at 1:00 am.
2 Comments.
Filed under space exploration, moon.
People often ask me, “How can the flag on the Moon wave if there is no air?” Well, that would be a good question, if the flag actually waved on the Moon. People see the image shown here, and it looks like the astronaut is standing beside a flag that is standing out straight in a stiff breeze. That is what it is supposed to look like! However, there is no wind at all. So, how does the flag stay extended like that?
Well, quite simply, NASA wanted to have a flag to plant in the lunar surface. There is no wind, so the flag would just hang there limp. That would not be very impressive. Also, it would be just a swatch of colored fabric in photos. There would be no way to tell that it was an American flag. So, they came up with an ingenious way of sticking a
flag in the surface that looked like it were waving. The fabric of the flag has a wire mesh sewn into it. The flag rolls up into a nice little package. When on the Moon, the astronauts extend the pole and stick it into the ground. They can then unroll the flag. Working in heavy spacesuits, though, it is easier to unroll the flag and then stick it into the ground. The lunar surface is grainular and tough to poke the flag into. So, they have to rock the pole back and forth shoving it down into the ground. Watching on the TV, this back and forth motion makes the flag swing back and forth like it is waving.
The wire mesh is sewn into the fabric so that the flag will appear to stand out straight in the absense of wind. But, a flag sticking straight out from the pole doesn’t look natural. So, the astronauts often would extend the flag and bend ripples into it so that it looked more like it were w
aving. Look at video of the astronauts moving around the flag. It looks like it is waving, but it is frozen in position as the astronauts move by. It doesn’t actually wave. As it turns out, the flag didn’t really unroll as smoothly on the Moon as it did in tests on Earth, so the astronauts didn’t have to do much work to make it look like it were waving. It tended to look crinkly anyway.
My final image is of the flag left by Apollo 11, as seen from the lunar lander. Without weather, one would expect that this scene would remain like this forever. But, that isn’t quite what happened. When the ascent module took off, the blast from the exhaust of the rocket engine blew over the flag. Just before it blew over, the blast shook it. This is the only time that the flag actually waved while on the Moon — while it was being blasted 
with rocket exhaust. Also, sadly, I would imagine that it probably isn’t red, white, and blue anymore. Likely the intense ultraviolet light from the Sun has faded the colors, just as it does to flags on Earth. But, without the protection of the Earth’s atmosphere, the ultraviolet light on the Moon is far stronger than it is on Earth, so I would be rather surprised if after this much time any color is left.
-Astroprof
Images courtesy of NASA
Andrew on 13 Aug 2006 at 2:05 pm: 1
What type of material was the flag made with?.I also wonder if with so much UV light,if it has become essentially dust at this point.Leaving of course, the mesh woven into the fabric behind?.
Astroprof on 13 Aug 2006 at 3:39 pm: 2
You might be right. I don’t know if it is true of all six flags, but the Apollo 11 flag started off as a simple requisition of a standard government issue nylon flag. Nylon will break down in UV. So, perhaps there isn’t much left now.