In the book "The Hobbit" (some of you may have heard of it) on the map of the Lonely Mountain were moon letters, letters that can only be read by the light of the moon at a certain phase.
Maybe moon letters could actually be made. Phase specificity would be hard, but making letters specific to moonlight should be possible.
The basis of this would be metameric pairs of pigments. Some pigments appear to be the same color in one lighting condition, but appear different in another.
What would be required would be sets of colors that all appeared the same in moonlight, but different in any other lighting. Also, a second set where If they were intermixed on the page with colors that appeared the different from the original set in moonlight, but the same or similar (close enough to mask the writing) in other light conditions, then moon writing would be possible.-- talldave, Jun 07 2008 Natural Light Sources http://www.schneide...lichtqeuellen_e.htmA short discussion of photographic challenges of various natural light sources. [talldave, Jun 08 2008] moon color http://en.allexpert...60/moon-color-1.htmA discussion on how to photograph subtle difference in the moon's color. [talldave, Jun 08 2008] Color Matching http://www.extremet...0,3973,13764,00.aspMetamerism and Metameric Pairs [talldave, Jun 09 2008] Black metamers http://www.wipo.int...021862&DISPLAY=DESCA page addressing the idea of using metamers for watermarking [talldave, Jun 09 2008] Moonlight? Moonlight? Isn't that sunlight reflected off the moon?-- normzone, Jun 07 2008 According to various websites, the color temperature of the moon is different than it is for the sun.
Yes moonlight is reflected sunlight, but it isn't perfectly reflected sunlight.-- talldave, Jun 08 2008 It's not just a matter of colour temperature. It's a whole spectral response.
Your Moon's reflected light will be missing some of the frequencies present in sunlight (since reflective effects are subtractive).
You'd need to identify the "gaps" in the moonlight spectrum, then use pigments where the presence of photons of thet "gap" energy produced zero contrast.
Might just be workable, but effects like cloud absorbtion or using reflected light of a concrete wall might produce the same effect as moonlight.....-- 8th of 7, Jun 08 2008 Moonlight is polarized during the first and third quarter phases. Maybe you could use that effect for your secret lunar spycode?-- wagster, Jun 08 2008 WTCTTISITMWIBNIIWR + magic. Sorry dave. I don't think it'll work.-- jaksplat, Jun 08 2008 No, it's not "magic". Blended inks with tailored spectral reponses are not uncommon. It might just be possible, just rather impractical.-- 8th of 7, Jun 08 2008 Since the ozone layer filters out all of the ultra violet from reflected sunlight would it not be possible to make a photo sensitive paper that would remain opaque in any natural light but moonlight? or a paint that would remain clear unless lit by the moon?
"pedo mellon a minno" (+)-- 2 fries shy of a happy meal, Jun 08 2008 If it was possible, it would be a little like those test you take to tell if you are color blind, the Ishihara Test for Color Blindness.
But the idea is that in most lighting conditions the pattern would be indistinct. But under the lighting conditions of the moon some groups of colors would match up.
Since some things appear to be the same color in some lighting conditions and appear different in others perhaps this could be exploited to produce lines to write out a message that is only visible in certain lighting conditions.-- talldave, Jun 09 2008 Whether it's possible or not is moot. The idea is not orginal.-- phoenix, Jun 09 2008 Doing it by magic isn't original.
Doing it by science (that is, for real), maybe is not totally original, but is a different matter.-- talldave, Jun 09 2008 random, halfbakery