# Where does light on the dark side of the moon come from? **URL:** \ **Category:** Factual Questions\ **Created:** [May 11, 2005, 3:06pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394 "2005-05-11T15:06:40Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Standup\_Karmic](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Standup\_Karmic](https://boards.straightdope.com/u/Standup_Karmic)\ **Post date:** [May 11, 2005, 3:06pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/1 "2005-05-11T15:06:40Z")
Looked up at the sky last evening. There was a little sliver of the moon lit up. I was also able to see the rest of the lunar circle, though the “dark” side was very dim. Where does the light come from to brighten the other side of the moon? Reflection of light cast upon the earth? ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [May 11, 2005, 3:11pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/2 "2005-05-11T15:11:01Z")
> [@](#): > > Where does the light come from to brighten the other side of the moon? Reflection of light cast upon the earth? Got it in one! ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [May 11, 2005, 3:22pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/3 "2005-05-11T15:22:18Z")
[Earthshine could shed light on global warming: Scientists use glow on moon’s dark side to measure clouds](http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2004/05/28/MNG136TB1P1.DTL) ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [May 11, 2005, 6:34pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/4 "2005-05-11T18:34:52Z")
Note that there are two ways in which “dark side” of the moon is used: the hemisphere that is not illuminated by the sun, and the hemisphere that we never see from the earth (which in fact does receive its fair share of sunlight). ---
**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\ **Post date:** [May 11, 2005, 6:43pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/5 "2005-05-11T18:43:28Z")
> [@Xema](#): > > Note that there are two ways in which “dark side” of the moon is used: the hemisphere that is not illuminated by the sun, and the hemisphere that we never see from the earth (which in fact does receive its fair share of sunlight). Someone please correct me if I’m wrong. But while there is a side of the moon that we never see from the earth, I thought I knew that there is NOT a side of the moon that receives no light from the sun. There is a hemisphere that isn’t lit right now, but that’s the same idea as night here. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [May 11, 2005, 7:04pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/6 "2005-05-11T19:04:14Z")
You aren’t wrong, just possibly that it could be stated a little less ambiguously. There’s dark and there’s dark. The dark side of the moon is is a colloqualism for the side we can’t see from earth. It doesn’t change location relative to the moon. It gets just as much light as the side we see over the course of a lunar cycle. The dark side of the moon in the sense that is isn’t illuminated by the sun is a hemisphere too, but unlike the north/south/east/west hemispheres on earth which are defined as fixed that dark side is constantly moving. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [May 11, 2005, 7:08pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/7 "2005-05-11T19:08:51Z")
> [@Tastes of Chocolate](#): > > Someone please correct me if I’m wrong. That’s correct. In fact, there’s a peak at the lunar pole [where the sun never sets.](http://news.bbc.co.uk/2/hi/science/nature/3549667.stm) ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [May 11, 2005, 7:11pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/8 "2005-05-11T19:11:58Z")
**Tastes of Chocolate** , you’re right. What Xema’s statement means is (with my modifications in **bold** ) “the hemisphere that is **at a given moment** not illuminated by the sun”, not “the hemisphere that is **never** illuminated by the sun”. ---
**Author:** ![tim314](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim314/32/3468_2.png) [@tim314](https://boards.straightdope.com/u/tim314)\ **Post date:** [May 11, 2005, 7:19pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/9 "2005-05-11T19:19:58Z")
> [@Tastes of Chocolate](#): > > Someone please correct me if I’m wrong. But while there is a side of the moon that we never see from the earth, I thought I knew that there is NOT a side of the moon that receives no light from the sun. There is a hemisphere that isn’t lit right now, but that’s the same idea as night here. You’re correct. “Dark side of the moon” is kind of a misnomer. Both sides experience both day and night (although it changes from day to night much more slowly, since the moon isn’t rotating as fast as the Earth is). I would guess that the term comes from a misconception that one side of the moon is always dark, and that the phases of the moon are due to the dark side and then the light side rotating into our view. In reality, one side of the moon always faces us, it’s just that sometimes it’s lit and sometimes it’s not. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 11, 2005, 10:30pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/10 "2005-05-11T22:30:39Z")
As testimony to my ignorance, let me ask - since the moon and earth are “locked” in their respective orbits, doesn’t that mean we, in fact, only ever see one side of the moon? If so, I’m not sure I understand the answers above which seem to imply we should be able to see _all_ the moon’s surface over some suitable interval. Thanks. ---
**Author:** ![mittu](https://avatars.discourse-cdn.com/v4/letter/m/ecd19e/32.png) [@mittu](https://boards.straightdope.com/u/mittu)\ **Post date:** [May 11, 2005, 10:42pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/11 "2005-05-11T22:42:13Z")
Yeah we only see one side of the moon, actually due to tilting I believe we see more like 55% of the surface over the course of a year. ---
**Author:** ![mittu](https://avatars.discourse-cdn.com/v4/letter/m/ecd19e/32.png) [@mittu](https://boards.straightdope.com/u/mittu)\ **Post date:** [May 11, 2005, 10:45pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/12 "2005-05-11T22:45:34Z")
Here’s a quote to clear things up on how we can see more than 50% of the surface. > [@](#): > > This lunar “libration” occurs, in part, because the orbit of the Moon is not round. When the moon is farther from Earth (apogee) its orbital motion is slower and can’t keep up with rotation so we see farther around the left side of the Moon. When the Moon is closer to Earth (perigee), orbital motion is faster and rotation can’t keep up with revolution and we see farther around the right side. In addition, the orbit of the Moon is tilted with reference to ours. When the Moon is below the plane of our orbit we look “down” on it and see a little more behind the upper edge, and when it is above, we look “up” at it and see a little more behind the lower edge. Overall, we get to see 59% of the surface of the Moon. Taken from [here](http://www.enerdynet.com/cgi-bin/product/stuff.cgi?db=stuff&uid=default&ww=on&id=30&view_records=1) ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [May 11, 2005, 11:02pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/13 "2005-05-11T23:02:48Z")
rowrrbazzle is quite right, and my statement sould have been clearer than it was. To summarize: There is a hemisphere (actually, just 41% as noted by mittu) of the moon that is never visible from the earth. This is often referred to as “the dark sideof the moon” even though it gets essenially the same amount of sunlight as the rest of the moon. (It obviously gets no “earthlight.”) At any moment (except during a lunar eclipse) something close to half the moon is illuminated by the sun. It thus follows that the other half is dark (except for “earthlight”) and can thus also be spoken of as “the dark side of the moon.” ---
**Author:** ![Dark\_Side\_of\_the\_Floyd](https://avatars.discourse-cdn.com/v4/letter/d/bb73d2/32.png) [@Dark\_Side\_of\_the\_Floyd](https://boards.straightdope.com/u/Dark_Side_of_the_Floyd)\ **Post date:** [May 11, 2005, 11:48pm UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/14 "2005-05-11T23:48:04Z")
Grrmf…will…not… ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [May 12, 2005, 12:04am UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/15 "2005-05-12T00:04:24Z")
Here’s a photographic gif animation showing the [Moon’s libration](http://epod.usra.edu/archive/epodviewer.php3?oid=233824) over an 11 day period. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [May 12, 2005, 12:11am UTC](https://boards.straightdope.com/t/where-does-light-on-the-dark-side-of-the-moon-come-from/303394/16 "2005-05-12T00:11:35Z")
A casual google finds an oodleplex of references to “far side of the moon”, which is clearly a more useful term.