<p>The lunar phase is based on the "age" of the moon since the last new moon. Any illumination up until a first quarter moon will look crescent-shaped, without any "nose". This crescent shape is a result of the positions of the Sun, Earth, and Moon in space. So, we can both observe and calculate the percent illumination and the shape of that illumination. In this particular case, the lunar terminator was running through a lunar mare, making it seem like the terminator was distorted. </p>

CC BY-SA 4.0
2018-09-17T00:15:12.930Z
2018-09-17T00:15:12.930Z
Alphecca
<p>Here's an image I captured from a Moon globe app on my iPad.</p>

<p><a href="https://i.sstatic.net/YnPN5.png" rel="noreferrer"><img src="https://i.sstatic.net/YnPN5.png" alt="enter image description here"></a></p>

<p>From your description, I think you may be referring to the southern rim of <a href="https://en.wikipedia.org/wiki/Mare_Tranquillitatis" rel="noreferrer">Mare Tranquillitatis</a>, the Sea of Tranquility, perhaps extending a little into the <a href="https://en.wikipedia.org/wiki/Hypatia_(crater)" rel="noreferrer">Rimae Hypatia</a>. This is an area which is lower than the surrounding mountains and craters, into which the shadow is encroaching.</p>

<p>Incidentally, Mare Tranquillitatis is the region where Neil Armstrong and Buzz Aldrin landed on the Apollo 11 mission!</p>

CC BY-SA 4.0
2018-09-17T14:25:41.603Z
Seems like it was more Mare Serenitatis, but it makes sense. I wouldn't have thought that the mountains on the moon were high enough to create this kind of view
Anne Aunyme
CC BY-SA 4.0
2018-09-16T23:22:20.473Z
2018-09-16T23:22:20.473Z
Jim421616
<p>Yesterday evening, the moon from my place looked like this:</p>

<p><a href="https://i.sstatic.net/yk2jq.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/yk2jqm.jpg" width="300" alt="moon on september 2018, the 15th" /></a></p>

<p>Basically, instead of the crescent shape I am used to it looked like there was three tips: one at each extremity (as usual) and one in the middle between the two first ones. This picture shows the rough shape of the visible moon, with arrows pointing at all three tips:</p>

<p><a href="https://i.sstatic.net/Y9uWW.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Y9uWW.png" width="300" alt="annotated three tipped moon" /></a></p>

<p>What is the explanation of this?</p>

CC BY-SA 4.0
2018-09-17T02:19:44.327Z
As can be clearly seen, certain parts of the moon's illuminated surface are darker than others. So we have various degrees of light reflection on the illuminated side itself, plus a penumbral region, plus the completely dark side. (It's fifty shades of grey, basically).
Lucian
<the-moon>
Why does the half moon appear to have a "nose"?
Anne Aunyme
# Why does the half moon appear to have a "nose"?

(Asked by: username_0 on 2018-09-16)

Yesterday evening, the moon from my place looked like this:

[![moon on september 2018, the 15th](https://i.sstatic.net/yk2jqm.jpg)](https://i.sstatic.net/yk2jq.jpg)

Basically, instead of the crescent shape I am used to it looked like there was three tips: one at each extremity (as usual) and one in the middle between the two first ones. This picture shows the rough shape of the visible moon, with arrows pointing at all three tips:

[![annotated three tipped moon](https://i.sstatic.net/Y9uWW.png)](https://i.sstatic.net/Y9uWW.png)

What is the explanation of this?

**Tags:** the-moon
> **Comments:**
> **username_1**: As can be clearly seen, certain parts of the moon's illuminated surface are darker than others. So we have various degrees of light reflection on the illuminated side itself, plus a penumbral region, plus the completely dark side. (It's fifty shades of grey, basically).  

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## 2 answers

### Answer by username_3 on 2018-09-16. Score: 6 | Accepted answer

Here's an image I captured from a Moon globe app on my iPad.

[![enter image description here](https://i.sstatic.net/YnPN5.png)](https://i.sstatic.net/YnPN5.png)

From your description, I think you may be referring to the southern rim of [Mare Tranquillitatis](https://en.wikipedia.org/wiki/Mare_Tranquillitatis), the Sea of Tranquility, perhaps extending a little into the [Rimae Hypatia](https://en.wikipedia.org/wiki/Hypatia_(crater)). This is an area which is lower than the surrounding mountains and craters, into which the shadow is encroaching.

Incidentally, Mare Tranquillitatis is the region where Neil Armstrong and Buzz Aldrin landed on the Apollo 11 mission!

> **Comments:**
> **username_0**: Seems like it was more Mare Serenitatis, but it makes sense. I wouldn't have thought that the mountains on the moon were high enough to create this kind of view  

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### Answer by username_2 on 2018-09-17. Score: 3

The lunar phase is based on the "age" of the moon since the last new moon. Any illumination up until a first quarter moon will look crescent-shaped, without any "nose". This crescent shape is a result of the positions of the Sun, Earth, and Moon in space. So, we can both observe and calculate the percent illumination and the shape of that illumination. In this particular case, the lunar terminator was running through a lunar mare, making it seem like the terminator was distorted.


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