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?
Got it in one!
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.
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.
That’s correct. In fact, there’s a peak at the lunar pole where the sun never sets.
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”.
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.
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.
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.
Here’s a quote to clear things up on how we can see more than 50% of the surface.
Taken from here
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.”
Grrmf…will…not…
Here’s a photographic gif animation showing the Moon’s libration over an 11 day period.
A casual google finds an oodleplex of references to “far side of the moon”, which is clearly a more useful term.