<p>As uhoh has written in the comments, this phenomenon is known as &quot;planetshine&quot;, and in this case more specifically &quot;earthshine&quot;. The sunlight hits the earth and is reflected to the moon, illuminating what cannot be directly reached by the sunlight.</p>
<p><a href="https://i.sstatic.net/x4hvG.png" rel="noreferrer"><img src="https://i.sstatic.net/x4hvG.png" alt="enter image description here" /></a></p>
<p><a href="https://en.wikipedia.org/wiki/Planetshine" rel="noreferrer">https://en.wikipedia.org/wiki/Planetshine</a></p>
<p><a href="https://en.wikipedia.org/wiki/Earthlight_(astronomy)" rel="noreferrer">https://en.wikipedia.org/wiki/Earthlight_(astronomy)</a></p>

CC BY-SA 4.0
2020-07-30T12:21:43.767Z
of course there *still is* always the possibility that your "brain made it up, as if it was trying to 'close the circle'" but I think the chances are low ;-)
uhoh
CC BY-SA 4.0
2020-07-30T18:15:00.593Z
A bit unrelated, but here https://www.researchgate.net/figure/Demonstration-of-illusory-contours-which-create-the-clear-perception-of-Gestalts-The_fig6_264866231 is an image whose optical illusion relies on the brain making up/completing things
jng224
CC BY-SA 4.0
2020-07-31T07:58:37.313Z
An additional point about your brain "making it up" - the dark side of the moon would have blocked out any stars behind it, making an area that could be distinguished from the rest of the stars.
IronEagle
CC BY-SA 4.0
2020-07-31T08:26:10.583Z
How come then we only see the edge slightly lit and not the whole dark side? The pictures posted in the comments show all, but in my experience I see only the edge of the dark side lit
Hakaishin
CC BY-SA 4.0
2020-07-31T18:16:28.647Z
@Hakaishin Previously: https://astronomy.stackexchange.com/questions/1622/why-is-the-outline-of-a-crescent-moon-brighter (This is about the bright part, but I think the answers apply equally to the dark part.)
user3067860
CC BY-SA 4.0
2020-08-03T07:10:02.977Z
@Araucaria-Nothereanymore. technically you're right... but *I am* the OP .
bgusach
CC BY-SA 4.0
2020-08-03T08:30:30.997Z
Ha ha. Oops +1!
Araucaria - Not here any more.
CC BY-SA 4.0
2020-07-30T09:43:29.597Z
2020-07-30T09:56:52.147Z
2020-07-30T09:56:52.147Z
bgusach
<p>Here's a very overexposed image of the old Moon in the new Moon's arms.</p>
<p><a href="https://www.flickr.com/photos/doegox/5507240324" rel="noreferrer">https://www.flickr.com/photos/doegox/5507240324</a></p>
<p>The bright side is the overexposed sunlit side. The dimly lit side is a result of the bright Earth shining in the Moon's sky.</p>
<p>The Earth lights up the Moon's surface as does the Moon light up the Earth at night, except the Earth is much brighter in the Moon's sky than the Moon is in the Earth's sky.</p>


CC BY-SA 4.0
2020-07-31T02:17:54.000Z
That's really, *really* beautiful!
uhoh
CC BY-SA 4.0
2020-07-30T18:19:30.010Z
2020-07-31T09:21:44.667Z
2020-07-31T09:21:44.667Z
L d Bonnie
<p>Yes, it is pretty visible in the right conditions.</p>
<p>And before you wonder if the dark side is visibly smaller - yes, it is. A peculiarity of the human vision makes brighter objects larger.</p>

CC BY-SA 4.0
2020-07-30T18:09:57.990Z
2020-07-30T18:09:57.990Z
fraxinus
<p>Some days ago, about 1 ~ 1.5 hours after the sunset I could see a very bright half moon, and the interesting part is, I <em>think</em> I could see the edge of the dark half of the moon, i.e. a whole circle, but with very little contrast to the surrounding black space. It was very weak.</p>
<p>I'll use my impressive graphic design skills to try to explain it better:</p>
<p><a href="https://i.sstatic.net/1WlUn.png" rel="noreferrer"><img src="https://i.sstatic.net/1WlUn.png" alt="enter image description here" /></a></p>
<p>The line I'm talking about is that grey one on the left, closing the moon.</p>
<p>My hypotheses are:</p>
<ul>
<li>My brain made it up, as if it was trying to &quot;close the circle&quot;</li>
<li>The earth was lighting the moon up, as in: light from the sun was hitting the earth and being re-emitted to the moon (as a very bright moon can actually provide you enough light to see in the dark).</li>
</ul>
<p>Thanks!</p>

CC BY-SA 4.0
2020-07-30T09:00:03.717Z
Have a look at https://en.wikipedia.org/wiki/Planetshine It is always okay to post an answer to your own question if you like :-)
uhoh
CC BY-SA 4.0
2020-07-30T09:43:53.633Z
@uhoh thank you very much! sometimes it's just a matter of finding the right term.
bgusach
CC BY-SA 4.0
2020-07-31T00:08:48.137Z
Here is an APOD (Astronomy Picture Of the Day) showing the phenomenon: https://apod.nasa.gov/apod/ap020419.html
Bit Chaser
CC BY-SA 4.0
2020-07-31T08:18:31.280Z
Not really related, yet quite fun (especially the caption): https://xkcd.com/1738/
DarioP
CC BY-SA 4.0
2020-08-02T13:44:30.237Z
My then-four year old noticed this just a few months ago. He exclaimed "I can see the moon's little baggie!" (אני רואה את השקית של הירח!‏), we've since enjoyed three additional new moons and each time he goes out to make what is now a joke.
dotancohen
<the-moon>
Is it possible to completely see the edge of a half moon at night?
bgusach
# Is it possible to completely see the edge of a half moon at night?

(Asked by: username_0 on 2020-07-30)

Some days ago, about 1 ~ 1.5 hours after the sunset I could see a very bright half moon, and the interesting part is, I *think* I could see the edge of the dark half of the moon, i.e. a whole circle, but with very little contrast to the surrounding black space. It was very weak.

I'll use my impressive graphic design skills to try to explain it better:

[![enter image description here](https://i.sstatic.net/1WlUn.png)](https://i.sstatic.net/1WlUn.png)

The line I'm talking about is that grey one on the left, closing the moon.

My hypotheses are:

* My brain made it up, as if it was trying to "close the circle"
* The earth was lighting the moon up, as in: light from the sun was hitting the earth and being re-emitted to the moon (as a very bright moon can actually provide you enough light to see in the dark).

Thanks!

**Tags:** the-moon
> **Comments:**
> **username_1**: Have a look at https://en.wikipedia.org/wiki/Planetshine It is always okay to post an answer to your own question if you like :-)  
> **username_0**: @uhoh thank you very much! sometimes it's just a matter of finding the right term.  
> **username_2**: Here is an APOD (Astronomy Picture Of the Day) showing the phenomenon: https://apod.nasa.gov/apod/ap020419.html  
> **username_3**: Not really related, yet quite fun (especially the caption): https://xkcd.com/1738/  
> **username_4**: My then-four year old noticed this just a few months ago. He exclaimed "I can see the moon's little baggie!" (אני רואה את השקית של הירח!‏), we've since enjoyed three additional new moons and each time he goes out to make what is now a joke.  

---

## 3 answers

### Answer by username_0 on 2020-07-30. Score: 23

As uhoh has written in the comments, this phenomenon is known as "planetshine", and in this case more specifically "earthshine". The sunlight hits the earth and is reflected to the moon, illuminating what cannot be directly reached by the sunlight.

[![enter image description here](https://i.sstatic.net/x4hvG.png)](https://i.sstatic.net/x4hvG.png)

<https://en.wikipedia.org/wiki/Planetshine>

<https://en.wikipedia.org/wiki/Earthlight_(astronomy)>

> **Comments:**
> **username_1**: of course there *still is* always the possibility that your "brain made it up, as if it was trying to 'close the circle'" but I think the chances are low ;-)  
> **username_5**: A bit unrelated, but here https://www.researchgate.net/figure/Demonstration-of-illusory-contours-which-create-the-clear-perception-of-Gestalts-The_fig6_264866231 is an image whose optical illusion relies on the brain making up/completing things  
> **username_6**: An additional point about your brain "making it up" - the dark side of the moon would have blocked out any stars behind it, making an area that could be distinguished from the rest of the stars.  
> **username_7**: How come then we only see the edge slightly lit and not the whole dark side? The pictures posted in the comments show all, but in my experience I see only the edge of the dark side lit  
> **username_8**: @Hakaishin Previously: https://astronomy.stackexchange.com/questions/1622/why-is-the-outline-of-a-crescent-moon-brighter (This is about the bright part, but I think the answers apply equally to the dark part.)  
> **username_0**: @Araucaria-Nothereanymore. technically you're right... but *I am* the OP .  
> **username_9**: Ha ha. Oops +1!  

---

### Answer by username_10 on 2020-07-30. Score: 13

Here's a very overexposed image of the old Moon in the new Moon's arms.

<https://www.flickr.com/photos/doegox/5507240324>

The bright side is the overexposed sunlit side. The dimly lit side is a result of the bright Earth shining in the Moon's sky.

The Earth lights up the Moon's surface as does the Moon light up the Earth at night, except the Earth is much brighter in the Moon's sky than the Moon is in the Earth's sky.

> **Comments:**
> **username_1**: That's really, *really* beautiful!  

---

### Answer by username_11 on 2020-07-30. Score: 10

Yes, it is pretty visible in the right conditions.

And before you wonder if the dark side is visibly smaller - yes, it is. A peculiarity of the human vision makes brighter objects larger.


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