MadSci Network: Engineering

Re: As the moon rotates, does the heat from the sun damage the USA flag?

Date: Thu May 8 21:28:05 2008
Posted By: James Griepenburg, , Chemical consultant, Chemmet Services
Area of science: Engineering
ID: 1209429016.Eg

As the Moon revolves in its orbit about the Earth it rotates once on its axis. The result, as you state, keeps the same side facing the Earth and causes 14 Earth-day days and nights on the moon. Since the Earth and the Moon are effectively the same distance from the Sun the heat input is about the same altho the reflectivities albedo] do differ somewhat.

The main difference is caused by our atmosphere. There are two big effects. The atmosphere absorbs most ultraviolet radiation below about 300 nm in wavelength and the atmosphere, especially water vapor and to a lessor extent the lower concentration greenhouse gases, CO2 and methane CH4] slow the re-radiation of infrared into space. Another factor is geothermal energy from our molten core and radioactive decay in the earth. [Because CO2 and CH4 are low in concentration small increases in their concentration have a more evident effect on the greenhouse effect; hence global warming]. The net result is that the Earth is warmer than the Moon with much lower variation in temperature and the wavelengths of light that can cause destruction of organic molecules are mostly filtered out.

Searching "moon flag" gives several references that explain some of this in detail. Here are several. A trip to the library and some Earth Science books will also help.

The Moon flags are made of Nylon [a better choice would be fiberglass] presumably Nylon66 that melts near 260C. This seems to be higher than the maximum temperatures on the moon so the flags probably haven't melted. However Nylon does absorb ultraviolet light so the high uv flux has probably destroyed the molecular structure of the polymer causing physical breakdown. Organic polymers don't do well in space, besides the uv near Earth orbits have significant concentrations of reactive atoms such as O and N from the breakup of the common molecules. These are very corrosive to organic materials. On the moon the concentrations of atoms are much lower but the Solar Wind is much more intense. This should cause more molecular destruction. And of course there are micrometeorites. The consensus seems to be that the flags are in rough shape by now.

I have probably missed other destruction mechanisms but it is possible that these processes are over-estimated and the flags are still standing.

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