<p>The Moon is so close that establishment of an atmosphere would be easy:</p>
<ul>
<li><p>you take a photo. An atmosphere always is thicker at the surface and gets exponentially thinner outward. This would be visible at the edges of the moon. Just think of the photos of Earth from space with the blue-ish layer the atmosphere shows as.<br>
It would also mean that the edges of the Moon would show in (slightly) different colour due to the presence of an atmosphere. Any atmosphere absorbs and scatters light. Especially the bluer light is scattered more efficiently (that's why the mountains in the distance show blue-ish). This would be visible in colour photography but - depending on the atmosphere's thickness - also with the visible eye.</p>
</li>
<li><p>even if you don't resolve the atmosphere: the Moon often passes in front of stars. The light curve of the stars can be captured when the Moon starts to obscure it. The drop is sharp and indicative of an edge. You would not see such diffraction pattern but a smooth transition from visible star to obscured star if the Moon had any significant atmosphere which causes scattering.<br>
Even easier this would be visible during a solar eclips. The edge of the shadow of the Moon would be less clear than it is.</p>
</li>
<li><p>Spectroscopy. Any atmosphere consists of atoms. Each atom has its own characteristic properties in absorption but also emission. The spectrum of daylight on Earth is characterized both, by the emission lines on the Sun, but also by the Fraunhofer absorption line in the Earth's atmosphere. No absorption of any kind is observed in the reflected light from the Moon.</p>
</li>
</ul>
<p>Neither of these observations needs very advanced equipment and can be made ground-based.</p>

CC BY-SA 4.0
2022-01-12T14:19:39.180Z
I wonder if the observation of [Baily's Beads](https://en.wikipedia.org/wiki/Baily%27s_beads) during total solar eclipses would also  be evidence of an atmosphere-less moon.
notovny
CC BY-SA 4.0
2022-01-12T14:45:32.577Z
@notovny doh! Sure enough, that's easier than stellar ocultations. Thanks, I added that.
planetmaker
CC BY-SA 4.0
2022-01-12T23:30:42.427Z
The solar spectrum is full of absorption lines superimposed on the underlying quasi-black body spectrum), including Fraunhofer lines. The reflected light from the moon includes all of that. It’s true that wouldn’t see O2 absorption (except that you’d still see O2 absorption from the Earth’s atmosphere, so it would be harder to rule out some additional contribution from a hypothetical thin lunar atmosphere).
Peter Erwin
CC BY-SA 4.0
2022-01-12T23:42:29.240Z
@PeterErwin it's no problem to measure the direct solar spectrum. Any difference from that must be attributed to the Moon. Sure enough, the thinner the atmosphere, and the more similar to Earth, the harder it is to detect with spectroscopy - but I recon still not a terribly hard task unless you get to atmospheric thicknesses where one can start calling it absence of an atmosphere.
planetmaker
CC BY-SA 4.0
2022-01-13T13:49:38.070Z
“Especially the bluer light is scattered more efficiently (that's why the mountains in the distance show blue-ish).” – actually it's the opposite: the mountains show more _yellowish_ because the blue components are scattered before reaching you. However, except for snow patches, mountains tend to be too dark-coloured for this to be much notable; what _is_ notable instead is the sunlight that also gets scattered from the air between mountain and observer. That has nothing to do with the mountains, but our eyes don't know that and interpret it as the mountains being blue.
leftaroundabout
CC BY-SA 4.0
2022-01-13T14:44:28.057Z
@leftaroundabout Depends on how you read it :) The blue-ish perception is because the air mass between you and the mountain scatters the blue light more efficiently. So the light which reaches you is the reflection from the mountain - slightly reddened due to scatter. But the blue overcompensated, because you add blue from the scatter of the air between you and the mountain. That's actually why the contrast of far-away mountains is so much worse than nearby ones, and why it appears more blue - effectively you have scattered blueish light superimposed on the slightly reddish mountain image.
planetmaker
CC BY-SA 4.0
2022-01-13T21:48:53.197Z
@planetmaker The points are: 1) "The spectrum of daylight on Earth is characterized ... by the emission lines on the Sun" is mostly wrong, since we don't see emission lines from the Sun unless we look very carefully (e.g., at the chromosphere) (and most of the "Fraunhofer lines" are *not* "in the Earth's atmosphere") ; and 2) Reflected sunlight from the Moon *observed from the ground on Earth* will have absorption from molecules in the Earth's atmosphere at some of the same wavelengths as from (hypothetical) molecular in a lunar atmosphere.
Peter Erwin
CC BY-SA 4.0
2022-01-12T14:05:07.283Z
2022-01-12T14:45:07.800Z
2022-01-12T14:45:07.800Z
planetmaker
<h3>19th century observers determined that the Moon is (almost totally) airless using 19th century instruments and observing techniques.</h3>
<p><a href="https://en.wikipedia.org/wiki/Roger_Joseph_Boscovich" rel="nofollow noreferrer">Roger Joseph Boscovich</a> (1711-1787) is credited with having discovered that the Moon has no atmosphere in 1753.</p>
<p>Wilhelm Beer and <a href="https://en.wikipedia.org/wiki/Johann_Heinrich_von_M%C3%A4dler" rel="nofollow noreferrer">Johann Heinrich Mädler</a> established <a href="https://en.wikipedia.org/wiki/Exploration_of_the_Moon#Before_spaceflight" rel="nofollow noreferrer">the same conclusion in the 1830s</a>:</p>
<blockquote>
<p>They also produced the first exact map of the Moon, <em>Mappa Selenographica</em>, published in four volumes in 1834–1836. In 1837 a description of the Moon (<em>Der Mond</em>) was published. Both were the best descriptions of the Moon for many decades, not superseded until the map of Johann Friedrich Julius Schmidt in the 1870s. Beer and Mädler drew the firm conclusion that the features on the Moon do not change, and there is no atmosphere or water.</p>
</blockquote>
<p><em>The Guinness Book of Astronomy Facts &amp; Feats</em> by Patrick Moore (2nd edition, 1983) discusses solar prominences on page 17:</p>
<blockquote>
<p><strong>Prominences</strong> were first described in detail by the Swedish observerVassenius at the total eclipse of 1733, though he believed that they belongd to the Moon rather than the Sun. (They may have been seen earlier - by Stannyan in 1706, from Berne.)  It was only after the eclipse of 1842 that astronomers became certain that they were solar rather than lunar.</p>
</blockquote>
<p>Page 20 discusses the solar corona, visible during eclipses, which was long suspected to be the atmosphere of the Moon.</p>
<blockquote>
<p>After observing the eclipse of 16 june 1806 from Kinderhook, New York, the Spanish astronomer Don Jose Joaquin de Ferrer pointed out that if the corona were due to a lunar atmopshere, then the height of this atmosphere wuld have to be 50 times greater than that of the Earth, which was clearly unreasonable.  However, it was only after careful studies of the eclipses of 1842 and 1851 that the corana and the prominences were were show unmistakably to belong to the Sun rather than the Moon.</p>
</blockquote>
<p><em>Exploration of the Universe Brief Edition</em>, George Abell, 1964, 1969, discusses the lack of lunar atmosphere on page 184:</p>
<blockquote>
<p>Telescopic observations of the moon, as ell as observations from lunar probes, confirm its expected lack of an appreciable atmopshere.  On the earth the air scatters the sunlight around into a certain portion of its night side, producing a twilight zone.  On the moon there is no evidence such a twilight zone.  Furthermore,  when the moon occults (passes in front of) a star, the star's light is observed to blink out suddenly, rather than to do dim gradually as it would if had to shine thorugh an atmosphere around the moon.</p>
</blockquote>
<p><a href="https://en.wikipedia.org/wiki/Atmosphere_of_Triton" rel="nofollow noreferrer">Triton, the large moon of Neptune, has a very thin atmosphere</a>:</p>
<blockquote>
<p>Nitrogen is the main gas in Triton's atmosphere. The two other known components are methane and carbon monoxide, whose abundances are a few hundredths of a percent of that of the nitrogen.</p>
<p>Triton's atmosphere is well structured and global. The atmosphere extends up to 800 kilometers above the surface, where the exobase is located, and had a surface pressure of about 14 microbars as of 1989. This is only 1/70,000th of the surface pressure on Earth.</p>
</blockquote>
<p><em>Voyager 2</em>  photographed atmospheric haze over the horizon of Triton.</p>
<p>It also photographed streaks of dark atmospheric material being blown by winds in the <a href="https://en.wikipedia.org/wiki/Atmosphere_of_Triton" rel="nofollow noreferrer">atmosphere of Triton</a>.</p>
<p>Presumably if the lunar atmosphere was as dense as even the ultra thin atmosphere of Triton it would have visible effects.</p>
<p>It is easy and simple to calculate and predict the Moon's orbit roughly.  But the precise orbital motions of the Moon is much more complicated to calculate and predict.  Those complex calculations are known as lunar theory.</p>
<p><a href="https://en.wikipedia.org/wiki/Peter_Andreas_Hansen" rel="nofollow noreferrer">Peter Andreas Hansen</a> (1795-1874) was a famous astronomer. Hansen worked out a new version of the lunar theory in the late 1850s which predicted all the lunar movements perfectly - for a few years.  And one of the features of Hansen's theory was that the Moon was sort of egg shaped (it is, but not that much) and the near side of the moon is sort of like a giant mountain projecting toward the Earth, and thus father from the center of the moon than the far side is.</p>
<p>That would mean that the near side would be sticking out above the lunar atmosphere and all the lunar atmosphere would be on the far side of the Moon, and hidden from Earth by the bulk of the Moon.</p>
<p><a href="https://en.wikipedia.org/wiki/Simon_Newcomb" rel="nofollow noreferrer">Simon Newcomb</a> (1835-1909) soon <a href="https://www.tandfonline.com/doi/abs/10.1080/00033798400200361?needAccess=true&amp;journalCode=tasc20" rel="nofollow noreferrer">refuted that theory of the shape of the Moon</a>. This was mentioned by <em>The Cornhill Magazine</em> in 1877 on page 724]<a href="https://books.google.com/books?id=DDQFAAAAQAAJ&amp;pg=PA724&amp;lpg=PA724&amp;dq=Hansen%20theory%20of%20the%20shape%20of%20the%20moon&amp;source=bl&amp;ots=UJ31pU9X5P&amp;sig=ACfU3U2s2_ULrDMzBDkNveUat-EDVe5aDQ&amp;hl=en&amp;sa=X&amp;ved=2ahUKEwiN-bKWnK31AhUEm-AKHQCRCQI4ChDoAXoECBQQAw#v=onepage&amp;q=Hansen%20theory%20of%20the%20shape%20of%20the%20moon&amp;f=false" rel="nofollow noreferrer">8</a>.</p>
<p>H.P. Lovecraft (1890-1937) once wrote that when he was 12 (c. 1902) he wrote a story where there was air on the far side of the Moon, even though he knew that Hansen's theory was false.  And Lovecraft was probably far from the last person to write a story where there was air and water and life on the far side of the Moon.  For example, the <em>Lunar Trilogy</em> by Jerzy Zulawsky (1901-1911) features a far side of the Moon with atmosphere.</p>
<p><a href="https://en.wikipedia.org/wiki/The_Lunar_Trilogy" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/The_Lunar_Trilogy</a></p>

CC BY-SA 4.0
2022-01-14T19:54:57.763Z
There are numerous typos in several of your book quotes. Did you type up the quoted text manually (and thus made errors in transcription), or are those errors in the original books you're quoting?
V2Blast
CC BY-SA 4.0
2022-01-15T19:13:35.767Z
I don't remember.  I must have typed out the quotes from books that I own, and copied the quotes from online sources.  For some reason I keep writing atmopshere instead of atmosphere.
M. A. Golding
CC BY-SA 4.0
2022-01-12T20:32:21.890Z
2022-01-18T08:10:06.000Z
2022-01-18T08:10:06.000Z
M. A. Golding
<p>The Moon doesn't have any significant atmosphere (surface pressure is <span class="math-container">$3\times10^{-15}$</span> bar). Can the absence of atmosphere on the Moon be determined with ground-based observations? When was it first determined that the Moon doesn't have an atmosphere, and with what data?</p>

CC BY-SA 4.0
2022-01-13T12:17:06.173Z
Seems like the kind of thing someone would have noticed during a solar eclipse.
RBarryYoung
CC BY-SA 4.0
2022-01-14T11:30:53.397Z
When you say "ground-based", do you mean the ground on Earth or on the Moon?
Parrotmaster
<observational-astronomy><the-moon>
What ground-based observational evidence is there that the Moon doesn't have an atmosphere?
usernumber
# What ground-based observational evidence is there that the Moon doesn't have an atmosphere?

(Asked by: username_0 on 2022-01-12)

The Moon doesn't have any significant atmosphere (surface pressure is $3\times10^{-15}$ bar). Can the absence of atmosphere on the Moon be determined with ground-based observations? When was it first determined that the Moon doesn't have an atmosphere, and with what data?

**Tags:** observational-astronomy, the-moon

> **Comments:**
> **username_1**: Seems like the kind of thing someone would have noticed during a solar eclipse.  
> **username_2**: When you say "ground-based", do you mean the ground on Earth or on the Moon?  

---

## 2 answers

### Answer by username_7 on 2022-01-12. Score: 27 | Accepted answer

### 19th century observers determined that the Moon is (almost totally) airless using 19th century instruments and observing techniques.

[Roger Joseph Boscovich](https://en.wikipedia.org/wiki/Roger_Joseph_Boscovich) (1711-1787) is credited with having discovered that the Moon has no atmosphere in 1753.

Wilhelm Beer and [Johann Heinrich Mädler](https://en.wikipedia.org/wiki/Johann_Heinrich_von_M%C3%A4dler) established [the same conclusion in the 1830s](https://en.wikipedia.org/wiki/Exploration_of_the_Moon#Before_spaceflight):

> They also produced the first exact map of the Moon, *Mappa Selenographica*, published in four volumes in 1834–1836. In 1837 a description of the Moon (*Der Mond*) was published. Both were the best descriptions of the Moon for many decades, not superseded until the map of Johann Friedrich Julius Schmidt in the 1870s. Beer and Mädler drew the firm conclusion that the features on the Moon do not change, and there is no atmosphere or water.

*The Guinness Book of Astronomy Facts & Feats* by Patrick Moore (2nd edition, 1983) discusses solar prominences on page 17:

> **Prominences** were first described in detail by the Swedish observerVassenius at the total eclipse of 1733, though he believed that they belongd to the Moon rather than the Sun. (They may have been seen earlier - by Stannyan in 1706, from Berne.) It was only after the eclipse of 1842 that astronomers became certain that they were solar rather than lunar.

Page 20 discusses the solar corona, visible during eclipses, which was long suspected to be the atmosphere of the Moon.

> After observing the eclipse of 16 june 1806 from Kinderhook, New York, the Spanish astronomer Don Jose Joaquin de Ferrer pointed out that if the corona were due to a lunar atmopshere, then the height of this atmosphere wuld have to be 50 times greater than that of the Earth, which was clearly unreasonable. However, it was only after careful studies of the eclipses of 1842 and 1851 that the corana and the prominences were were show unmistakably to belong to the Sun rather than the Moon.

*Exploration of the Universe Brief Edition*, George Abell, 1964, 1969, discusses the lack of lunar atmosphere on page 184:

> Telescopic observations of the moon, as ell as observations from lunar probes, confirm its expected lack of an appreciable atmopshere. On the earth the air scatters the sunlight around into a certain portion of its night side, producing a twilight zone. On the moon there is no evidence such a twilight zone. Furthermore, when the moon occults (passes in front of) a star, the star's light is observed to blink out suddenly, rather than to do dim gradually as it would if had to shine thorugh an atmosphere around the moon.

[Triton, the large moon of Neptune, has a very thin atmosphere](https://en.wikipedia.org/wiki/Atmosphere_of_Triton):

> Nitrogen is the main gas in Triton's atmosphere. The two other known components are methane and carbon monoxide, whose abundances are a few hundredths of a percent of that of the nitrogen.
>
> Triton's atmosphere is well structured and global. The atmosphere extends up to 800 kilometers above the surface, where the exobase is located, and had a surface pressure of about 14 microbars as of 1989. This is only 1/70,000th of the surface pressure on Earth.

*Voyager 2* photographed atmospheric haze over the horizon of Triton.

It also photographed streaks of dark atmospheric material being blown by winds in the [atmosphere of Triton](https://en.wikipedia.org/wiki/Atmosphere_of_Triton).

Presumably if the lunar atmosphere was as dense as even the ultra thin atmosphere of Triton it would have visible effects.

It is easy and simple to calculate and predict the Moon's orbit roughly. But the precise orbital motions of the Moon is much more complicated to calculate and predict. Those complex calculations are known as lunar theory.

[Peter Andreas Hansen](https://en.wikipedia.org/wiki/Peter_Andreas_Hansen) (1795-1874) was a famous astronomer. Hansen worked out a new version of the lunar theory in the late 1850s which predicted all the lunar movements perfectly - for a few years. And one of the features of Hansen's theory was that the Moon was sort of egg shaped (it is, but not that much) and the near side of the moon is sort of like a giant mountain projecting toward the Earth, and thus father from the center of the moon than the far side is.

That would mean that the near side would be sticking out above the lunar atmosphere and all the lunar atmosphere would be on the far side of the Moon, and hidden from Earth by the bulk of the Moon.

[Simon Newcomb](https://en.wikipedia.org/wiki/Simon_Newcomb) (1835-1909) soon [refuted that theory of the shape of the Moon](https://www.tandfonline.com/doi/abs/10.1080/00033798400200361?needAccess=true&journalCode=tasc20). This was mentioned by *The Cornhill Magazine* in 1877 on page 724][8](https://books.google.com/books?id=DDQFAAAAQAAJ&pg=PA724&lpg=PA724&dq=Hansen%20theory%20of%20the%20shape%20of%20the%20moon&source=bl&ots=UJ31pU9X5P&sig=ACfU3U2s2_ULrDMzBDkNveUat-EDVe5aDQ&hl=en&sa=X&ved=2ahUKEwiN-bKWnK31AhUEm-AKHQCRCQI4ChDoAXoECBQQAw#v=onepage&q=Hansen%20theory%20of%20the%20shape%20of%20the%20moon&f=false).

H.P. Lovecraft (1890-1937) once wrote that when he was 12 (c. 1902) he wrote a story where there was air on the far side of the Moon, even though he knew that Hansen's theory was false. And Lovecraft was probably far from the last person to write a story where there was air and water and life on the far side of the Moon. For example, the *Lunar Trilogy* by Jerzy Zulawsky (1901-1911) features a far side of the Moon with atmosphere.

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

> **Comments:**
> **username_8**: There are numerous typos in several of your book quotes. Did you type up the quoted text manually (and thus made errors in transcription), or are those errors in the original books you're quoting?  
> **username_7**: I don't remember.  I must have typed out the quotes from books that I own, and copied the quotes from online sources.  For some reason I keep writing atmopshere instead of atmosphere.  

---

### Answer by username_3 on 2022-01-12. Score: 44

The Moon is so close that establishment of an atmosphere would be easy:

* you take a photo. An atmosphere always is thicker at the surface and gets exponentially thinner outward. This would be visible at the edges of the moon. Just think of the photos of Earth from space with the blue-ish layer the atmosphere shows as.  
  It would also mean that the edges of the Moon would show in (slightly) different colour due to the presence of an atmosphere. Any atmosphere absorbs and scatters light. Especially the bluer light is scattered more efficiently (that's why the mountains in the distance show blue-ish). This would be visible in colour photography but - depending on the atmosphere's thickness - also with the visible eye.
* even if you don't resolve the atmosphere: the Moon often passes in front of stars. The light curve of the stars can be captured when the Moon starts to obscure it. The drop is sharp and indicative of an edge. You would not see such diffraction pattern but a smooth transition from visible star to obscured star if the Moon had any significant atmosphere which causes scattering.  
  Even easier this would be visible during a solar eclips. The edge of the shadow of the Moon would be less clear than it is.
* Spectroscopy. Any atmosphere consists of atoms. Each atom has its own characteristic properties in absorption but also emission. The spectrum of daylight on Earth is characterized both, by the emission lines on the Sun, but also by the Fraunhofer absorption line in the Earth's atmosphere. No absorption of any kind is observed in the reflected light from the Moon.

Neither of these observations needs very advanced equipment and can be made ground-based.

> **Comments:**
> **username_4**: I wonder if the observation of [Baily's Beads](https://en.wikipedia.org/wiki/Baily%27s_beads) during total solar eclipses would also  be evidence of an atmosphere-less moon.  
> **username_3**: @username_4 doh! Sure enough, that's easier than stellar ocultations. Thanks, I added that.  
> **username_5**: The solar spectrum is full of absorption lines superimposed on the underlying quasi-black body spectrum), including Fraunhofer lines. The reflected light from the moon includes all of that. It’s true that wouldn’t see O2 absorption (except that you’d still see O2 absorption from the Earth’s atmosphere, so it would be harder to rule out some additional contribution from a hypothetical thin lunar atmosphere).  
> **username_3**: @PeterErwin it's no problem to measure the direct solar spectrum. Any difference from that must be attributed to the Moon. Sure enough, the thinner the atmosphere, and the more similar to Earth, the harder it is to detect with spectroscopy - but I recon still not a terribly hard task unless you get to atmospheric thicknesses where one can start calling it absence of an atmosphere.  
> **username_6**: “Especially the bluer light is scattered more efficiently (that's why the mountains in the distance show blue-ish).” – actually it's the opposite: the mountains show more _yellowish_ because the blue components are scattered before reaching you. However, except for snow patches, mountains tend to be too dark-coloured for this to be much notable; what _is_ notable instead is the sunlight that also gets scattered from the air between mountain and observer. That has nothing to do with the mountains, but our eyes don't know that and interpret it as the mountains being blue.  
> **username_3**: @username_6 Depends on how you read it :) The blue-ish perception is because the air mass between you and the mountain scatters the blue light more efficiently. So the light which reaches you is the reflection from the mountain - slightly reddened due to scatter. But the blue overcompensated, because you add blue from the scatter of the air between you and the mountain. That's actually why the contrast of far-away mountains is so much worse than nearby ones, and why it appears more blue - effectively you have scattered blueish light superimposed on the slightly reddish mountain image.  
> **username_5**: @username_3 The points are: 1) "The spectrum of daylight on Earth is characterized ... by the emission lines on the Sun" is mostly wrong, since we don't see emission lines from the Sun unless we look very carefully (e.g., at the chromosphere) (and most of the "Fraunhofer lines" are *not* "in the Earth's atmosphere") ; and 2) Reflected sunlight from the Moon *observed from the ground on Earth* will have absorption from molecules in the Earth's atmosphere at some of the same wavelengths as from (hypothetical) molecular in a lunar atmosphere.  

---

