"A giant moonbeam reflector may shine away depression" is the title of a widely-linked recent Popular Science piece, about one Richard Chapin and his colossal array of allegedly therapeutic moon-mirrors.

Go and read it. It's worth it just for the picture, which makes clear that this thing could probably cook a whole cow pretty fast during the day.

Shining away depression reminds me of good-byeing it, which is cheering. But the piece itself, and the people talking about it, are as usual contributing to my depression by being impressively uninformed.

Oh, and by encouraging sick and desperate people to trek out into the Arizonan desert to be bathed in purest placebo, rather than doing (a) something that might actually impede the progress of their disease or (b) something more fun.

Yes, the moonbeam reflector is just silly on its face; strange ideas about moonlight are, in an etymologically deterministic sort of way, quite popular among lunatics. But Popular Science, at least, should have run their article past someone with a high school science education, so they wouldn't say stupid things like "moonlight's frequency and spectrum are unique".

Well, yes, moonlight does have a unique spectrum, in the sense that sunlight that bounces off anything has a unique spectrum. Sunlight that bounces off my foot today has a different spectrum from sunlight that bounced off my foot yesterday. Just not very different.

What "frequency" is supposed to mean in this context, though, is entirely beyond me. By definition, something with a "spectrum" does not have one frequency.

And if you take the "unique spectrum" to mean that there's anything very interesting about the spectrum of moonlight, you're wrong. For the wavelengths normal mirrors can reflect, moonlight's spectrum is essentially the same as that of sunlight bouncing off any other grey rock. It's not as if the moon has an atmosphere that absorbs certain wavebands, after all. Moonlight is a plain old continuous spectrum, mildly polarised by reflection (but not polarised any more by reflection from the mirrors, since metallic surfaces do not polarise reflected light).

This is mentioned in passing here. Also, it stands to bloody reason. The moon is just a lot of grey rocks, for God's sake. It's like the world's biggest camera-calibrating grey card, though rather darker than the usual 18%.

(Although, actually, the moon's average full-moon 12%-ish albedo really does nicely match what many light meters are apparently calibrated for. Regrettably, you can't really carry the moon around with you, and people don't take a lot of sunlight-exposure photos when the full moon is visible.)

It's not very scientific to point out that long exposure colour photographs taken by moonlight look very much like short exposure photos taken by sunlight, but I might as well throw that in too, since I quite like this one I took...

Three Sisters apparently not by night 0238 hours on a full-moon morning.

There is, to be fair, a bit more to moon reflections than that. The albedo of airless rocky bodies is more complex than that of a piece of grey cardboard, as is explained in detail here. But I don't think any of this was news to astronomers 200 years ago, though they would doubtless recognise a big array of light-concentrating mirrors as being akin to the coloured light therapy that had been in use, worthlessly, for many centuries before. The invention of electric light reinvigorated this branch of quackery.

Like every good crackpot, Richard Chapin has a patent, which explains the details of his invention far better than any news piece is likely to.

3 Responses to “Moonshine”

  1. troglobyte Says:

    Although the "moonlight" thing seems like a crackpot idea of the first rate, there is quite a bit of evidence towards bright light therapy helping with seasonal affective disorder - a type of depression. Of course, the best way to get the necessary light during the darker months is typically via a box packed with high-intensity flourescent lights and a diffuser, and by natural sunlight during the summer.

    Incidentally, there does seem to be a form of "colored light therapy" that shows promise, as well. Apparently, there are receptors in the eye which aren't processed by the normal visual system - instead, they regulate melatonin production. They respond best to blue light, up near UV frequencies. Amusingly, while the "chromotherapy" folks claim that blue will calm you and help you sleep (at least according to that Wikipedia article), it seems it might be helpful in waking you up instead!

    Details here. I'm not going to look up the journal article right now; I'm tired and need sleep. The abstract is publically available if I remember right, though.

  2. Matt W Says:

    Apparently that big mirror(s) cost him USD2m. Someone saw him coming !

  3. RichVR Says:

    His problem is that he's using an Interstellar Light Collector to collect Lunar Light. That can't be good.

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