<p>This is a bit rough, since I can't find the exact numbers anywhere.  However the lunar highlands have an albedo that is double the lunar mare  (about 0.2 compared to 0.1)(<a href="https://lunarpedia.org/w/Lunar_Albedo#:%7E:text=At%20the%20angles%20we%20can,bright%20ejecta%20and%20highland%20regions." rel="nofollow noreferrer">source</a>). The far side is almost completely highland, so its albedo is about 0.2</p>
<p>But only about 1/3 of the nearside is lunar mare (<a href="https://www.lpi.usra.edu/exploration/education/hsResearch/presentations/2014_2015/Posters/Beaverton.pdf" rel="nofollow noreferrer">source</a>).</p>
<p>So  the relevant calculation is <span class="math-container">$(1/3×0.1 +2/3×0.2)\div 0.2 =0.83$</span>  That is the nearside is 83% of the far side in albedo.  Or the far side is 20% brighter.</p>
<p>In terms of magnitude, a 20% increase in brightness corresponds to about 0.2 magnitudes brighter. The full moon has magnitude -12.7, so a far side full moon would have magnitude -12.9.</p>
<p>These are fairly rough figures, but the impression is that a &quot;far-side&quot; moon would be brighter, but not exceptionally brighter than the moon as we see it now.</p>

CC BY-SA 4.0
2023-08-10T22:01:02.710Z
This would make the albedo of the near side 0.167, while the highest number you can find for this is 0.137. Source: https://the-moon.us/wiki/Albedo.
George Lee
CC BY-SA 4.0
2023-08-10T23:51:52.810Z
Yes, this is all a bit rough,  I think that's within the kind of error boundaries I imagined for this calculation. You could reduce the number "0.2" to 0.17, and see if that makes a  difference
James K
CC BY-SA 4.0
2023-08-11T09:53:43.493Z
This study should be useful to you: https://articles.adsabs.harvard.edu//full/1968SvA....11.1034L/0001040.000.html
Nilay Ghosh
CC BY-SA 4.0
2023-08-11T19:50:27.837Z
The LRO ( Lunar Reconnaissance Orbiter) has gathered a ton of lunar albedo data, eg the LAMP data, but I think it's mostly looking at UV albedo (because it's looking for water). https://lunar.gsfc.nasa.gov/dataproducts.html
PM 2Ring
CC BY-SA 4.0
2023-08-11T21:07:12.973Z
Yes, but it's local, not integrated over a whole hemisphere.  One could do the integration, and perhaps someone has, but I can't find it.  If someone does find it, I'd encourage them to write an answer.
James K
CC BY-SA 4.0
2023-08-11T22:03:42.583Z
The sheer amount of LRO data is seriously scary. ;) Maybe some expert knows about integrated albedo data, but I'm definitely not going to try searching for it on a phone...
PM 2Ring
CC BY-SA 4.0
2023-08-10T21:19:37.597Z
2023-08-10T21:19:37.597Z
James K
<p>We may be able to shed some light on this question by looking at the magnitude of the Moon from the <a href="https://en.wikipedia.org/wiki/Lunar_Reconnaissance_Orbiter" rel="nofollow noreferrer">Lunar Reconnaissance Orbiter</a> (LRO).</p>
<p>Ideally, we'd like data from a satellite in a high altitude equatorial orbit, but the LRO is in a polar orbit (inclination ~85.2° to the lunar equator), and it has a rather low altitude. Its semi-major axis is ~1830 km, but the Moon's radius is ~1737.4 km. Wikipedia claims that the LRO is in an eccentric orbit, but that information is out of date, and its current eccentricity is ~0.00129, but admittedly its altitude deviates from that of a simple Kepler ellipse, due to the lunar <a href="https://en.wikipedia.org/wiki/Mass_concentration_(astronomy)" rel="nofollow noreferrer">mascons</a>. The inclination of its orbit is currently quite stable, though.</p>
<p>The LRO has JPL Horizons ID -85. Its trajectory data was recently updated, on 2023-Aug-3. You can see its osculating orbit elements for 2023-Aug-1 18:30 TDB <a href="https://ssd.jpl.nasa.gov/api/horizons.api?format=text&amp;MAKE_EPHEM=YES&amp;COMMAND=-85&amp;EPHEM_TYPE=E&amp;CENTER=500%40301&amp;TLIST_TYPE=CAL&amp;TLIST=%272023-Aug-1+18%3A30%27&amp;REF_PLANE=BODY" rel="nofollow noreferrer">here</a>. That time is close to the most recent full moon (2023-Aug-1 18:31:40 UTC).</p>
<p>The LRO has a sidereal period of almost 2 hours (1h 57m 2.9s). Here's a plot showing its distance from the centre of the Moon, covering 6 hours, with a 2 minute timestep.</p>
<p><a href="https://i.sstatic.net/KKg1G.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/KKg1G.png" alt="LRO-Moon distance" /></a>
I made that plot using the script <a href="https://astronomy.stackexchange.com/a/49267/16685">here</a>. I have a magnitude plotting script <a href="https://astronomy.stackexchange.com/a/53620/16685">here</a>.</p>
<p>When it's full moon, the far side is dark. When it's new moon the far side is fully illuminated. So we can get a rough idea of the difference in albedo by looking at the magnitude of the Moon at those times.</p>
<p>Here's a Moon magnitude plot covering the same timespan (using the same timestep).</p>
<p><a href="https://i.sstatic.net/JgZcB.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JgZcB.png" alt="Moon magnitude, Full" /></a></p>
<p>And here is the corresponding plot for the previous new moon (2023-Jul-17 18:32:50 UTC).</p>
<p><a href="https://i.sstatic.net/z73Yb.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/z73Yb.png" alt="Moon magnitude, New" /></a></p>
<p>The mean magnitude on the new moon is -21.466, which is slightly brighter than the full moon mean of -21.168. Interestingly, the peak magnitude at full moon is slightly higher than at new moon. The minima during the new moon are noticeably brighter that at full moon. I assume that's mostly due to earthshine.</p>
<p>However, Horizons doesn't say how it computes these magnitudes, and it gives this warning:</p>
<blockquote>
<p>Moon's approximate apparent visual magnitude and surface brightness. When phase angle &lt; 7 deg (within ~1 day of full Moon), computed magnitude tends to be about 0.12 too small.</p>
</blockquote>

CC BY-SA 4.0
2023-08-11T21:59:56.860Z
You can plot LRO's orbit in 3D using my script at the end of this answer: https://astronomy.stackexchange.com/a/49823/16685
PM 2Ring
CC BY-SA 4.0
2023-08-11T22:17:47.010Z
I understand that the magnitude plots include when the LRO was at the dark side of the Moon. So what causes the brightness of over -17? And does that make the data unreliable?
George Lee
CC BY-SA 4.0
2023-08-12T00:27:59.333Z
@George I'm not sure why Horizons gives such a high brightness over the whole orbit. It *shouldn't* be getting any sunlight when it's in the middle of the night side. It's altitude is ~100 km, so the Moon should completely block the Sun.
PM 2Ring
CC BY-SA 4.0
2023-08-14T16:11:43.933Z
So I'm afraid that we can't accept anything from that data as is.
George Lee
CC BY-SA 4.0
2023-08-11T21:58:12.517Z
2023-08-11T22:46:17.867Z
2023-08-11T22:46:17.867Z
PM 2Ring
<p>As is well known, and as you can see in the image below, the far side of the Moon is brighter than its near side. What is its overall albedo? And what would be the magnitude of a full moon if the (current) far side were facing us? <a href="https://i.sstatic.net/iaO3B.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/iaO3B.jpg" alt="sides of moon" /></a></p>

CC BY-SA 4.0
2023-08-09T16:46:02.930Z
Magnitude means nothing here unless you specify where from. From Earth, presumably but you need to make this clear.
adrianmcmenamin
CC BY-SA 4.0
2023-08-09T20:40:12.753Z
Oh no! The far side cannot be seen from earth! I mean when facing the far side, so the moon is between you and earth.
George Lee
CC BY-SA 4.0
2023-08-10T10:34:12.147Z
I know the far side cannot be seen from Earth. This is why your question is poorly specified. Unless you define a distance then the magnitude question is impossible to answer - from a long way away is Moon will be very dim for instance.
adrianmcmenamin
CC BY-SA 4.0
2023-08-10T20:43:02.187Z
ok, edited, I hope its clear enough now.
George Lee
CC BY-SA 4.0
2023-08-11T09:42:39.710Z
Related: https://astronomy.stackexchange.com/questions/41264/why-would-the-side-of-the-moon-that-faces-earth-be-as-dark-as-the-far-side-of-th
Nilay Ghosh
CC BY-SA 4.0
2023-08-11T22:02:18.963Z
@NilayGhosh **Not related**. Don't judge a question by its title.
George Lee
CC BY-SA 4.0
2023-08-12T02:53:30.893Z
How is it not related? I don't judge questions by title rather I do from content. I believe the answer from JohnHunt on that question explains this.
Nilay Ghosh
CC BY-SA 4.0
2023-08-14T16:07:12.600Z
@NilayGhosh John Hunt apparently did read only the title of the question. However, he is definitely not **answering** my question.
George Lee
<the-moon><albedo>
What is the albedo of the far side of the Moon?
George Lee
# What is the albedo of the far side of the Moon?

(Asked by: username_0 on 2023-08-06)

As is well known, and as you can see in the image below, the far side of the Moon is brighter than its near side. What is its overall albedo? And what would be the magnitude of a full moon if the (current) far side were facing us? [![sides of moon](https://i.sstatic.net/iaO3B.jpg)](https://i.sstatic.net/iaO3B.jpg)

**Tags:** the-moon, albedo

> **Comments:**
> **username_1**: Magnitude means nothing here unless you specify where from. From Earth, presumably but you need to make this clear.  
> **username_0**: Oh no! The far side cannot be seen from earth! I mean when facing the far side, so the moon is between you and earth.  
> **username_1**: I know the far side cannot be seen from Earth. This is why your question is poorly specified. Unless you define a distance then the magnitude question is impossible to answer - from a long way away is Moon will be very dim for instance.  
> **username_0**: ok, edited, I hope its clear enough now.  
> **username_2**: Related: https://astronomy.stackexchange.com/questions/41264/why-would-the-side-of-the-moon-that-faces-earth-be-as-dark-as-the-far-side-of-th  
> **username_0**: @NilayGhosh **Not related**. Don't judge a question by its title.  
> **username_2**: How is it not related? I don't judge questions by title rather I do from content. I believe the answer from JohnHunt on that question explains this.  
> **username_0**: @NilayGhosh John Hunt apparently did read only the title of the question. However, he is definitely not **answering** my question.  

---

## 2 answers

### Answer by username_3 on 2023-08-10. Score: 4

This is a bit rough, since I can't find the exact numbers anywhere. However the lunar highlands have an albedo that is double the lunar mare (about 0.2 compared to 0.1)([source](https://lunarpedia.org/w/Lunar_Albedo#:%7E:text=At%20the%20angles%20we%20can,bright%20ejecta%20and%20highland%20regions.)). The far side is almost completely highland, so its albedo is about 0.2

But only about 1/3 of the nearside is lunar mare ([source](https://www.lpi.usra.edu/exploration/education/hsResearch/presentations/2014_2015/Posters/Beaverton.pdf)).

So the relevant calculation is $(1/3×0.1 +2/3×0.2)\div 0.2 =0.83$ That is the nearside is 83% of the far side in albedo. Or the far side is 20% brighter.

In terms of magnitude, a 20% increase in brightness corresponds to about 0.2 magnitudes brighter. The full moon has magnitude -12.7, so a far side full moon would have magnitude -12.9.

These are fairly rough figures, but the impression is that a "far-side" moon would be brighter, but not exceptionally brighter than the moon as we see it now.

> **Comments:**
> **username_0**: This would make the albedo of the near side 0.167, while the highest number you can find for this is 0.137. Source: https://the-moon.us/wiki/Albedo.  
> **username_3**: Yes, this is all a bit rough,  I think that's within the kind of error boundaries I imagined for this calculation. You could reduce the number "0.2" to 0.17, and see if that makes a  difference  
> **username_2**: This study should be useful to you: https://articles.adsabs.harvard.edu//full/1968SvA....11.1034L/0001040.000.html  
> **username_4**: The LRO ( Lunar Reconnaissance Orbiter) has gathered a ton of lunar albedo data, eg the LAMP data, but I think it's mostly looking at UV albedo (because it's looking for water). https://lunar.gsfc.nasa.gov/dataproducts.html  
> **username_3**: Yes, but it's local, not integrated over a whole hemisphere.  One could do the integration, and perhaps someone has, but I can't find it.  If someone does find it, I'd encourage them to write an answer.  
> **username_4**: The sheer amount of LRO data is seriously scary. ;) Maybe some expert knows about integrated albedo data, but I'm definitely not going to try searching for it on a phone...  

---

### Answer by username_4 on 2023-08-11. Score: 2

We may be able to shed some light on this question by looking at the magnitude of the Moon from the [Lunar Reconnaissance Orbiter](https://en.wikipedia.org/wiki/Lunar_Reconnaissance_Orbiter) (LRO).

Ideally, we'd like data from a satellite in a high altitude equatorial orbit, but the LRO is in a polar orbit (inclination ~85.2° to the lunar equator), and it has a rather low altitude. Its semi-major axis is ~1830 km, but the Moon's radius is ~1737.4 km. Wikipedia claims that the LRO is in an eccentric orbit, but that information is out of date, and its current eccentricity is ~0.00129, but admittedly its altitude deviates from that of a simple Kepler ellipse, due to the lunar [mascons](https://en.wikipedia.org/wiki/Mass_concentration_(astronomy)). The inclination of its orbit is currently quite stable, though.

The LRO has JPL Horizons ID -85. Its trajectory data was recently updated, on 2023-Aug-3. You can see its osculating orbit elements for 2023-Aug-1 18:30 TDB [here](https://ssd.jpl.nasa.gov/api/horizons.api?format=text&MAKE_EPHEM=YES&COMMAND=-85&EPHEM_TYPE=E&CENTER=500%40301&TLIST_TYPE=CAL&TLIST=%272023-Aug-1+18%3A30%27&REF_PLANE=BODY). That time is close to the most recent full moon (2023-Aug-1 18:31:40 UTC).

The LRO has a sidereal period of almost 2 hours (1h 57m 2.9s). Here's a plot showing its distance from the centre of the Moon, covering 6 hours, with a 2 minute timestep.

[![LRO-Moon distance](https://i.sstatic.net/KKg1G.png)](https://i.sstatic.net/KKg1G.png)
I made that plot using the script [here](https://astronomy.stackexchange.com/a/49267/16685). I have a magnitude plotting script [here](https://astronomy.stackexchange.com/a/53620/16685).

When it's full moon, the far side is dark. When it's new moon the far side is fully illuminated. So we can get a rough idea of the difference in albedo by looking at the magnitude of the Moon at those times.

Here's a Moon magnitude plot covering the same timespan (using the same timestep).

[![Moon magnitude, Full](https://i.sstatic.net/JgZcB.png)](https://i.sstatic.net/JgZcB.png)

And here is the corresponding plot for the previous new moon (2023-Jul-17 18:32:50 UTC).

[![Moon magnitude, New](https://i.sstatic.net/z73Yb.png)](https://i.sstatic.net/z73Yb.png)

The mean magnitude on the new moon is -21.466, which is slightly brighter than the full moon mean of -21.168. Interestingly, the peak magnitude at full moon is slightly higher than at new moon. The minima during the new moon are noticeably brighter that at full moon. I assume that's mostly due to earthshine.

However, Horizons doesn't say how it computes these magnitudes, and it gives this warning:

> Moon's approximate apparent visual magnitude and surface brightness. When phase angle < 7 deg (within ~1 day of full Moon), computed magnitude tends to be about 0.12 too small.

> **Comments:**
> **username_4**: You can plot LRO's orbit in 3D using my script at the end of this answer: https://astronomy.stackexchange.com/a/49823/16685  
> **username_0**: I understand that the magnitude plots include when the LRO was at the dark side of the Moon. So what causes the brightness of over -17? And does that make the data unreliable?  
> **username_4**: @George I'm not sure why Horizons gives such a high brightness over the whole orbit. It *shouldn't* be getting any sunlight when it's in the middle of the night side. It's altitude is ~100 km, so the Moon should completely block the Sun.  
> **username_0**: So I'm afraid that we can't accept anything from that data as is.  

---

