# Why is the moon white? **URL:** \ **Category:** Factual Questions\ **Created:** [August 4, 2007, 5:16am UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398 "2007-08-04T05:16:45Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [August 4, 2007, 5:16am UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/1 "2007-08-04T05:16:45Z")
Ever since its formation, the surface of the moon has been bombarded with all sorts of rocks. Presumably, each of these rocks has a color, depending on its place of origin. Even if, upon impact, it would be pulverized and plunged beneath the surface, kicking up white moon dust, eventually it too would become part of the dust. So shouldn’t the moon’s surface be more colorful than it is? ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [August 4, 2007, 5:28am UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/2 "2007-08-04T05:28:08Z")
It isn’t white. It’s a pale gray, like most of the minerals that compose its surface. (Ever see any moon rocks the astronauts brought back? About as visually boring as rocks and dust can be.) It just looks white compared with the night sky. Its albedo, or the amount of sunlight it reflects, is actually quite low at .12 (12%) or so. Were it like Venus, with an albedo of .65/65% you’d have trouble sleeping. Though not really, because you’d be used to it. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [August 4, 2007, 5:29am UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/3 "2007-08-04T05:29:47Z")
From wiki: > [@](#): > > Another quirk of the visual system causes us to see the Moon as almost pure white, when in fact it reflects only about 7% of the light falling on it (about as dark as a lump of coal). It has a very low albedo. Color constancy in the visual system recalibrates the relations between the colours of an object and its surroundings; however, there is nothing next to the Moon to reflect the light falling on the Moon; therefore it is perceived as the brightest object visible. We have no standard to compare it to. An example of this is that, if you used a narrow beam of light to illuminate a lump of coal in a dark room, it would look white. If you then broadened the beam of the light source to illuminate the surroundings, it would revert to black. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [August 4, 2007, 9:36am UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/4 "2007-08-04T09:36:14Z")
I have been told that the moon reflects about as much light as asphalt, which I guess ties up with the “lump of coal” reference. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [August 4, 2007, 12:26pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/5 "2007-08-04T12:26:37Z")
Ok, I understand all of that. But still, after being bombarded for eons, why aren’t there rocks of all different colors littering the surface of the Moon? ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [August 4, 2007, 12:57pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/6 "2007-08-04T12:57:16Z")
[QUOTE=Colophon] I have been told that the moon reflects about as much light as asphalt, which I guess ties up with the “lump of coal” reference. [/QUOTE] The phrase I remember from the period (Gah. Those synapses haven’t been exercised in thirty years!) was ‘well-weathered asphalt.’ Coal would sound darker. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [August 4, 2007, 3:39pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/7 "2007-08-04T15:39:53Z")
Because it reflects all of the colors of sunlight that fall on it pretty uniformly. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [August 4, 2007, 4:21pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/8 "2007-08-04T16:21:24Z")
[QUOTE=panache45] Ok, I understand all of that. But still, after being bombarded for eons, why aren’t there rocks of all different colors littering the surface of the Moon? [/QUOTE] Perhaps space rocks are all the same color. Earth rocks are formed through terrestrial processes, including sedimentation, vulcanism, metamorphic pressure and temperature. Space rocks are presumably formed under different conditions, so you would not expect to have hunks of granite, sandstone or marble impacting the Moon. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [August 4, 2007, 4:37pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/9 "2007-08-04T16:37:24Z")
[QUOTE=dropzone] It isn’t white. It’s a pale gray, . [/QUOTE] Nah,[it’s silvery.](http://www.ruthetting.com/songs/by-the-light-of-the-silvery-moon.asp) > [@](#): > > By the light of the silv’ry moon I want to spoon > To my honey I’ll croon love’s tune > Honey moon, keep a-shinin’ in June > Your silv’ry beams will bring love’s dreams > We’ll be cuddlin’ soon by the silv’ry moon > > Words by Ed Madden, Music by Gus Edwards (1919) ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [August 4, 2007, 4:38pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/10 "2007-08-04T16:38:16Z")
[QUOTE=David Simmons] Nah,[it’s silvery.](http://www.ruthetting.com/songs/by-the-light-of-the-silvery-moon.asp) [/QUOTE] I thought it was cheese-green. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [August 4, 2007, 4:54pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/11 "2007-08-04T16:54:44Z")
[QUOTE=dropzone] Its albedo, or the amount of sunlight it reflects, is actually quite low at .12 (12%) or so. [/QUOTE] The moon is [about as reflective as a main belt asteroid](http://209.85.165.104/search?q=cache:wgrHHRr41p8J:sait.oat.ts.astro.it/MSAIS/6/PDF/133.pdf+asteroids+%22average+albedo%22&hl=en&ct=clnk&cd=9&gl=us&client=firefox-a): > [@](#): > > p[sub]v[/sub]=0.11, average albedo for main belt asteroids, and p[sub]v[/sub]=0.30, average albedo for NEAs (Delb`o 2004), respectively. The moon does have [areas of different colors](http://www.dslreports.com/forum/remark,16822681), they’re just not _very_ different. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [August 4, 2007, 6:01pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/12 "2007-08-04T18:01:06Z")
One of the Apollo missions brought back rocks that were orange. Don’t forget that the Moon is relatively stable, geologically speaking. There’s no tectonic plates to mix the surface up, so you’re not going to get much diversity in terms of lunar material. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [August 4, 2007, 7:21pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/13 "2007-08-04T19:21:18Z")
Google image search for moon+Apollo, and you’ll get any number of pictures from the moon landings, which give you a much better idea of the moon’s appearence close up. While writing a fantasy story, I once toyed with the idea of a world with two moons: the Bright Moon, which was limestone white and therefore brilliantly bright, and the Dark Moon, which was soot black and barely visible against the night sky. ---
**Author:** ![Sequent](https://avatars.discourse-cdn.com/v4/letter/s/dbc845/32.png) [@Sequent](https://boards.straightdope.com/u/Sequent)\ **Post date:** [August 4, 2007, 7:25pm UTC](https://boards.straightdope.com/t/why-is-the-moon-white/414398/14 "2007-08-04T19:25:31Z")
Also, the moon has a bit of a [dust problem](http://en.wikipedia.org/wiki/Lunar_soil) which might contribute significantly to the overall white-grey-silver-cheese appearance.