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The article reasoning can be shortened to observation that passive optical system does not change the wavelength of photons and to trigger a fire the wavelength
by fpoling 8y ago
The article reasoning can be shortened to observation that passive optical system does not change the wavelength of photons and to trigger a fire the wavelength has to be short enough.
But the conclusion of the article is wrong. The surface temperature of the Moon has very little to do with the wavelength of the reflected photons.
Consider a surface covered with ideal tiny mirrors each pointing to random direction. Only a tiny proportion of these mirrors will reflect light from the Sun towards observer. Now consider that 90% of those mirrors are painted black reducing the reflected enrrgy flux by further factor of ten. The Moon is like that.
Still the reflected light has original wavelength of the light of the Sun. Collect enough of it and that triggers fire.
- nshepperd 8y agoThat's incorrect. It has nothing to do with the wavelength of the light. > Still the reflected light has original wavelength of the light of the Sun. Collect enough of it and that triggers fire. You can't collect enough of it into one place with a passive optical system, because it's been irreversibly scattered by the moon's surface (Read: irreversible increase of https://en.wikipedia.org/wiki/Etendue https://en.wikipedia.org/wiki/Etendue).
- fpoling 8y agoYes, I stand corrected. Essentially an optical system will bring Moon's surface closer, but even if it brings the surface within 1 cm from the wood, the defused Sun light scattered from that surface is not enough to ignite the fire.