Why does the moon shine white?

kiwigavin · Feb 9, 2009

My mother-in-law blind-sided me with this. We'd had a day at KSC, seen Magnificent Desolation and the other lunar exhibits and she had noticed that they always refer to the lunar soil as being varying shades of grey. That night she noticed the near-full moon and asked "If it's so grey why does it appear white?". And "When are you going to get a proper job you no good bum?" I started to try and bluster about albedo and absorbtion of wavelengths and stuff but rapidly gave up. So there must be a simple answer to this: If the moon's soil is so grey, how come it shines white?

centsworth_II · Feb 9, 2009

Replying to: <DIV CLASS='Discussion_PostQuote'>That night she noticed the near-full moon and asked "If it's so grey why does it appear white?". Posted by kiwigavin</DIV>In normal room -- or display -- lighting, the true grey color is seen.  In the harsh glare of the sun, the color is washed out.  This is even seen on the surface of the moon in photos that are not purposely underexposed to bring out details.  <img src="http://sitelife.space.com/ver1.0/Content/images/store/8/6/78e2cef7-8cf3-421c-b612-357a7d175de1.Medium.jpg" alt="" /> <div class="Discussion_UserSignature"> </div>

MeteorWayne · Feb 9, 2009

Replying to: <DIV CLASS='Discussion_PostQuote'>My mother-in-law blind-sided me with this. We'd had a day at KSC, seen Magnificent Desolation and the other lunar exhibits and she had noticed that they always refer to the lunar soil as being varying shades of grey. That night she noticed the near-full moon and asked "If it's so grey why does it appear white?". And "When are you going to get a proper job you no good bum?" I started to try and bluster about albedo and absorbtion of wavelengths and stuff but rapidly gave up. So there must be a simple answer to this: If the moon's soil is so grey, how come it shines white?  Posted by kiwigavin</DIV> Well, you have to ask youself, what is grey?It is a flat spectrum at lower intensity than a white background.So against a black night sky, (or even a dimmer than the moon blue day sky) it just reflects the sunlight right back at you. Against either, it is a brighter "white" than the background.Note that during a solar eclipse, it appears black since it is darker than the background

Hope that helps!Wayne  <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

yevaud · Feb 9, 2009

I'll add to what Wayne said: ever wonder why a green plant looks, well, green?  It absorbs all bands except green.  In that visible band, it reflects strongly.  Simple.  So the composition of the Regolith of the surface of the moon reflects strongly in that particular visible band (bands, more correctly). <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

crazyeddie · Feb 9, 2009

Replying to: <DIV CLASS='Discussion_PostQuote'>My mother-in-law blind-sided me with this. We'd had a day at KSC, seen Magnificent Desolation and the other lunar exhibits and she had noticed that they always refer to the lunar soil as being varying shades of grey. That night she noticed the near-full moon and asked "If it's so grey why does it appear white?". And "When are you going to get a proper job you no good bum?" I started to try and bluster about albedo and absorbtion of wavelengths and stuff but rapidly gave up. So there must be a simple answer to this: If the moon's soil is so grey, how come it shines white?  Posted by kiwigavin</DIV>The various sections of the moon's surface actually does contain subtle variations of color, which can be enhanced with Photoshop and other imaging software:http://www.rc-astro.com/photo/id1018.htmlAlso, tell your mother-in-law that the moon doesn't always appear to "shine white".  Depending on it's location in the sky and on atmospheric phenomenon, such as dust at high altitudes, it can appear to be orange, red, or blue......and once, after the eruption of the volcano Krakatoa in 1883, it was reported that the moon took on a distinctly green appearance:Coincident with these atmospheric fluctuations, magnificent sunlight effects, lurid skies, prolonged dawns, and lengthened twilights were observed. The captain whose experience has here been given at some length states that on September 9, 1883, in latitude 140° N., longitude 114° E., the sun rose perfectly green, and so continued for forty-eight hours; and that the moon and the stars gave a green light as well. He also reports that he noticed peculiar red sunsets in the South Atlantic several weeks before the Java eruption, and that he carried them through to Hong Kong, and from there nearly across to San Francisco. The volcanic cloud that caused these peculiar effects seems to have followed a straight path, for they appeared on the east coast of Africa on the second day, on the Gold Coast on the third, at Trinidad on the sixth, and at Honolulu on the ninth day. It is impossible to say how high the lighter matter was carried; it is certain that months have been required for it to descend. The places situated below the direct path of the cloud were the first to have those ominous displays, which varied in intensity according to their time distance to the westward; for the cloud was at first elevated as a comparatively narrow column. This column gradually spread out north and south, until the inhabitants of all lands obtained a view of the beautiful effects of broken and absorbed sunbeams, and a demonstration of the power of that steam which was imprisoned by the last convulsion of nature.  http://www.theatlantic.com/issues/1884sep/sturdy.htm <div class="Discussion_UserSignature"> </div>

Saiph · Feb 9, 2009

As the other said, a combination of reflected spectrum, atmospheric affects and, oddly, biology. The eye tends to take bright light sources and normalize them to "white".  This can be seen with a lot of artificial lighting.  Compared directly to sunlight, the lighting in most offices has a green or yellow hue to it.  Not strong, but definetly there.  However, most of the time you are sequestered away from windows...and the light you see seems to be white enough.  The eye (or brain, or whatnot) tends to pick the predominate colors and flatten them out to use as a 'white' baseline when judging other colors.Most of the light from the moon is reflected sunlight, which is basically white (with yellow overtones), and is easily adapted to 'white' by our eyes.  Sure there are differences and variations...but it's typically washed out and hard for the eye to pick out.So you've got two big reasons:  Grey is basically white, and our eyes lie

<div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

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