Timeline for Why is the surface of the Moon white?
Current License: CC BY-SA 3.0
14 events
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| Jul 13, 2015 at 16:49 | comment | added | ProfRob | @SteveJessop I've hedged my bets. The moon is certainly not grey (not even close) either in the sense of a flat spectrum or a flat reflectance spectrum. Some say that it should appear reddish, but the Purkinje effect or mesopic vision makes it appear grey. I now think that it appears grey (or white against a dark background if one prefers) simply because our eyes are incapable of resolving its colour as different to white, but I do not know enough eye physiology to be definitive. Both the answers I criticised say the moon is (not appears) grey without further discussion or demonstration. | |
| Jul 12, 2015 at 23:38 | comment | added | Steve Jessop | In this answer you say "could be considered pinkish", but conclude that the spectrum is "close enough" to be called white. Then in comments to other peoples' answers, as a critiscm, you say that the moon objectively is "not grey" since its spectrum is not precisely flat. This seems an uneven application of the meanings of colour-words. Once bright enough that colour vision kicks in, the moon is by definition exactly as grey as (ignoring the effect of Earth's atmosphere) its reflected light appears white, isn't it? That is to say, pretty grey. | |
| Jul 12, 2015 at 22:10 | comment | added | David Hammen | Sorry, I misread the first plot. And yes, our eyes are only so-so at seeing colors -- but we're very good at seeing shades, hues, and tints of green. | |
| Jul 12, 2015 at 20:49 | history | edited | ProfRob | CC BY-SA 3.0 |
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| Jul 12, 2015 at 20:37 | comment | added | ProfRob | @DavidHammen What first spectrum? The first plot is the reflectance. Yes the answer may well be as simple as "our eyes are incapable of distinguishing these two spectra as differently coloured". The moon appears white because sunlight appears white and the reflection modifies the spectrum insufficiently to make a difference. | |
| Jul 12, 2015 at 19:15 | comment | added | joojaa | its not purkinje but rather eyes adaptive white balance, which also makes it look nearly white. But then thats not physics is it? | |
| Jul 12, 2015 at 19:09 | comment | added | David Hammen | That second set of spectra looks much better than your first spectrum. Also note that the scale is linear. Our eyes are logarithmic devices. Those two spectra would be much closer to one another had intensity been placed on a logarithmic scale. | |
| Jul 12, 2015 at 18:21 | history | edited | ProfRob | CC BY-SA 3.0 |
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| Jul 12, 2015 at 18:03 | comment | added | ProfRob | @DavidHammen However, I do agree that even a preliminary bit of research does suggest that the brightness of the full moon surface ought to be enough to engage photopic vision. | |
| Jul 12, 2015 at 17:54 | comment | added | ProfRob | @DavidHammen Which spectrum do you refer to. I show the reflectance. To get the lunar spectrum you multiply the solar spectrum by this and then modify slightly for transmission through the Earth's atmosphere. The stars/planets you mention are very much redder than moonlight and appear only slightly red to the naked eye. They are fainter than the moon, but perhaps not orders of magnitude fainter when expressed in terms of surface brightness over the cells in the eye. (The moon is apparent mag about -5 per sq arcmin). | |
| Jul 12, 2015 at 17:33 | comment | added | David Hammen | There's something wrong with that article and with that spectrum. The Purkinje effect explanation is nonsense. That explains why a white car looks bluish under moonlight, but not moonlight itself. Mars is obviously red. So is Antares ("not Mars"), as is Betelgeuse. All three are orders of magnitude less luminous than is the Moon. | |
| Jul 12, 2015 at 11:41 | history | edited | ProfRob | CC BY-SA 3.0 |
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| Jul 12, 2015 at 10:36 | history | edited | ProfRob | CC BY-SA 3.0 |
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| Jul 12, 2015 at 8:29 | history | answered | ProfRob | CC BY-SA 3.0 |