<p>There are a few factors that create this effect:</p>

<p>First in the visual light images, the view around the equator is seen back lit, with almost no shadow, the few around the pole is seen with low lighting, and low lighting brings out features of the terrain. The Polar mosaics have an unreal quality, since they are made of images all taken when the sun is locally at its maximum above the horizon, so the light appears to be coming from all directions at once.</p>

<p>The first mosaic and the topographic map have a projection that is "conformal" this means that circular craters appear circular on the map, but it does introduce very large distortions of scale this, combined with shading which has been added to the map, makes regular-sized craters near the poles appear huge. The shading scales with the map, so craters near the pole have much more dramatic shading than those near the equator, that is an artistic effect, not real.</p>

<p>Finally on one face of the moon, that which faces us, and is in the middle of the pictures, there are large "maria". These are relatively flat lava plains. There are no maria at the poles. Most are on the near side of the moon: see <a href="https://astronomy.stackexchange.com/questions/1850/why-are-most-lunar-maria-on-the-visible-side?rq=1">Why are most lunar maria on the visible side?</a></p>

<p>So this is a combination of low angle of light at the poles, the way that google has projected and shaded their map and the distribution of lava plains on the moon. The poles are not more bumpy than the equatorial region in general. They are more bumpy that the lunar maria, but the apparent effect you describe is an illusion.</p>

CC BY-SA 3.0
2017-08-15T17:25:30.947Z
So is this an illusion caused by light angle and amplified by composite images? Are the Moon's poles more bumpy or not?
lolmaus - Andrey Mikhaylov
CC BY-SA 3.0
2017-08-15T17:50:55.983Z
They are not more bumpy than the equatorial region in general. They are more bumpy that the lunar maria. The apparent effect you describe is an illusion.
James K
CC BY-SA 3.0
2017-08-15T19:09:32.903Z
Thank you. Can you please emphasize your last comment in your answer, so that I can accept it?
lolmaus - Andrey Mikhaylov
CC BY-SA 3.0
2017-08-23T17:32:42.733Z
Please update your post with key conclusion that the apparent effect is an illusion.
lolmaus - Andrey Mikhaylov
CC BY-SA 3.0
2017-08-23T17:43:00.703Z
The last sentence "They are more bumpy that the lunar maria, but the apparent effect you describe is an illusion."
James K
CC BY-SA 3.0
2017-08-15T14:32:26.923Z
2017-08-15T20:33:51.840Z
2017-08-15T20:33:51.840Z
James K
<p>It looks as if it was polished by applying emery to its spinning equator.</p>

<p>My initial guess was that it was simply an illusion caused by light direction, but the terrain map shows the same phenomena.</p>

<h3>Google Moon photo and terrain maps (<a href="https://www.google.com/moon/" rel="nofollow noreferrer">source</a>)</h3>

<p><a href="https://i.sstatic.net/hQEBG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/hQEBG.png" alt="Google Moon photo map"></a><a href="https://i.sstatic.net/fDWvt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/fDWvt.png" alt="Google Moon terrain map"></a></p>

<p>North pole mosaic assembled from photos by NASA's Lunar Reconnaissance Orbiter (<a href="https://www.nasa.gov/content/nasa-releases-first-interactive-mosaic-of-lunar-north-pole" rel="nofollow noreferrer">source</a>):</p>

<h3><a href="https://www.nasa.gov/sites/default/files/gigapan_small_str01.png" rel="nofollow noreferrer"><img src="https://www.nasa.gov/sites/default/files/gigapan_small_str01.png" alt="North pole mosaic from NASA&#39;s Lunar Reconnaissance Orbiter"></a></h3>

<p>South pole shot by NASA's Clementine (<a href="https://svs.gsfc.nasa.gov/3443" rel="nofollow noreferrer">source</a>):</p>

<h3><a href="https://i.sstatic.net/N4Mst.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/N4Mst.jpg" alt="South pole shot by NASA&#39;s Clementine"></a></h3>

<the-moon><geology><topographic-map>
Why is the Moon smooth near the equator and bumpy near the poles?
lolmaus - Andrey Mikhaylov
# Why is the Moon smooth near the equator and bumpy near the poles?

(Asked by: username_0 on 2017-08-15)

It looks as if it was polished by applying emery to its spinning equator.

My initial guess was that it was simply an illusion caused by light direction, but the terrain map shows the same phenomena.

### Google Moon photo and terrain maps ([source](https://www.google.com/moon/))

[![Google Moon photo map](https://i.sstatic.net/hQEBG.png)](https://i.sstatic.net/hQEBG.png)[![Google Moon terrain map](https://i.sstatic.net/fDWvt.png)](https://i.sstatic.net/fDWvt.png)

North pole mosaic assembled from photos by NASA's Lunar Reconnaissance Orbiter ([source](https://www.nasa.gov/content/nasa-releases-first-interactive-mosaic-of-lunar-north-pole)):

### [North pole mosaic from NASA's Lunar Reconnaissance Orbiter](https://www.nasa.gov/sites/default/files/gigapan_small_str01.png)

South pole shot by NASA's Clementine ([source](https://svs.gsfc.nasa.gov/3443)):

### [South pole shot by NASA's Clementine](https://i.sstatic.net/N4Mst.jpg)

**Tags:** the-moon, geology, topographic-map


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## 1 answers

### Answer by username_1 on 2017-08-15. Score: 9 | Accepted answer

There are a few factors that create this effect:

First in the visual light images, the view around the equator is seen back lit, with almost no shadow, the few around the pole is seen with low lighting, and low lighting brings out features of the terrain. The Polar mosaics have an unreal quality, since they are made of images all taken when the sun is locally at its maximum above the horizon, so the light appears to be coming from all directions at once.

The first mosaic and the topographic map have a projection that is "conformal" this means that circular craters appear circular on the map, but it does introduce very large distortions of scale this, combined with shading which has been added to the map, makes regular-sized craters near the poles appear huge. The shading scales with the map, so craters near the pole have much more dramatic shading than those near the equator, that is an artistic effect, not real.

Finally on one face of the moon, that which faces us, and is in the middle of the pictures, there are large "maria". These are relatively flat lava plains. There are no maria at the poles. Most are on the near side of the moon: see [Why are most lunar maria on the visible side?](https://astronomy.stackexchange.com/questions/1850/why-are-most-lunar-maria-on-the-visible-side?rq=1)

So this is a combination of low angle of light at the poles, the way that google has projected and shaded their map and the distribution of lava plains on the moon. The poles are not more bumpy than the equatorial region in general. They are more bumpy that the lunar maria, but the apparent effect you describe is an illusion.

> **Comments:**
> **username_0**: So is this an illusion caused by light angle and amplified by composite images? Are the Moon's poles more bumpy or not?  
> **username_1**: They are not more bumpy than the equatorial region in general. They are more bumpy that the lunar maria. The apparent effect you describe is an illusion.  
> **username_0**: Thank you. Can you please emphasize your last comment in your answer, so that I can accept it?  
> **username_0**: Please update your post with key conclusion that the apparent effect is an illusion.  
> **username_1**: The last sentence "They are more bumpy that the lunar maria, but the apparent effect you describe is an illusion."  

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