<p>According to <a href="https://iopscience.iop.org/article/10.3847/1538-4357/aaafd5" rel="nofollow noreferrer">Formation of the UV Spectrum of Molecular Hydrogen in the Sun</a> (S. A. Jaeggli et al. 2018 ApJ <strong>855</strong> 134, also <a href="https://www.researchgate.net/publication/323142255_Formation_of_the_UV_Spectrum_of_Molecular_Hydrogen_in_the_Sun" rel="nofollow noreferrer">here</a>) molecular hydrogen in the sun was first spectroscopically discovered in 1977. The model calculation in this reference give a ratio molecular/atomic hydrogen of around <span class="math-container">$10^{-5}$</span> at a height of about 650 km (where the <span class="math-container">$H_2$</span> emissions have a maximum). Temperature at this height is taken as 4220K</p>
<p><a href="https://i.sstatic.net/G9HhQ.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/G9HhQ.jpg" alt="Figure 7. The normalized line contribution as a function of height
for the 100 brightest H2 lines between 1205 and 1550 °A from the
FALC×1 calculation." /></a></p>
<blockquote>
<p>Figure 7. The normalized line contribution as a function of height
for the 100 brightest <span class="math-container">$H_2$</span> lines between 1205 and 1550 °A from the
FALC×1 calculation. In general the lines originate in a 150 km
thick region centered at 650 km. Red lines originate slightly deeper
than blue lines in agreement with the wavelength dependence of
opacity, but some lines originate higher due to their excitation source</p>
</blockquote>

CC BY-SA 4.0
2021-07-27T07:28:40.343Z
@BenCrowell This figure refers to height of 650 km (where the H2 emissions have a maximum) See my edited answer
Thomas
CC BY-SA 4.0
2021-07-27T17:58:14.370Z
@uhoh See my edited answer
Thomas
CC BY-SA 4.0
2021-07-28T00:47:09.070Z
The paper is fascinating, excellent source! Since the original publication is open access I've added a direct link to it as well.
uhoh
CC BY-SA 4.0
2021-07-26T17:44:13.430Z
2021-07-28T00:44:35.950Z
2021-07-28T00:44:35.950Z
Thomas
<p>I don't have a license to practice chemistry, but I'll convert Wikipedia's <a href="https://en.wikipedia.org/wiki/Hydrogen#Reactants" rel="noreferrer">bond dissociation energy of 435.7 kJ/mol</a> to eV by dividing it by <span class="math-container">$C / N_A$</span> where <span class="math-container">$C$</span> is 1 Coulomb and <span class="math-container">$N_A$</span> is Avogadro's number, and I get about 4.5 eV which is pretty big.</p>
<p>Dividing that by the Boltzmann constant <span class="math-container">$k_B$</span> gives about 52,000 Kelvin, which is simultaneously hot compared to the Sun's photosphere's temperature of about ~5,800 Kelvin, and not hot compared to the Sun's corona temperature of roughly 5,000,000 Kelvin.</p>
<p>This suggest to me that since the Sun is mostly hydrogen, it makes sense to ask</p>
<p><strong>Question:</strong> Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?</p>

<observational-astronomy><the-sun><stellar-atmospheres>
Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?
uhoh
# Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?

(Asked by: username_0 on 2021-07-26)

I don't have a license to practice chemistry, but I'll convert Wikipedia's [bond dissociation energy of 435.7 kJ/mol](https://en.wikipedia.org/wiki/Hydrogen#Reactants) to eV by dividing it by $C / N\_A$ where $C$ is 1 Coulomb and $N\_A$ is Avogadro's number, and I get about 4.5 eV which is pretty big.

Dividing that by the Boltzmann constant $k\_B$ gives about 52,000 Kelvin, which is simultaneously hot compared to the Sun's photosphere's temperature of about ~5,800 Kelvin, and not hot compared to the Sun's corona temperature of roughly 5,000,000 Kelvin.

This suggest to me that since the Sun is mostly hydrogen, it makes sense to ask

**Question:** Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?

**Tags:** observational-astronomy, the-sun, stellar-atmospheres

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## 1 answers

### Answer by username_1 on 2021-07-26. Score: 5 | Accepted answer

According to [Formation of the UV Spectrum of Molecular Hydrogen in the Sun](https://iopscience.iop.org/article/10.3847/1538-4357/aaafd5) (S. A. Jaeggli et al. 2018 ApJ **855** 134, also [here](https://www.researchgate.net/publication/323142255_Formation_of_the_UV_Spectrum_of_Molecular_Hydrogen_in_the_Sun)) molecular hydrogen in the sun was first spectroscopically discovered in 1977. The model calculation in this reference give a ratio molecular/atomic hydrogen of around $10^{-5}$ at a height of about 650 km (where the $H\_2$ emissions have a maximum). Temperature at this height is taken as 4220K

[![Figure 7. The normalized line contribution as a function of height
for the 100 brightest H2 lines between 1205 and 1550 °A from the
FALC×1 calculation.](https://i.sstatic.net/G9HhQ.jpg)](https://i.sstatic.net/G9HhQ.jpg)

> Figure 7. The normalized line contribution as a function of height
> for the 100 brightest $H\_2$ lines between 1205 and 1550 °A from the
> FALC×1 calculation. In general the lines originate in a 150 km
> thick region centered at 650 km. Red lines originate slightly deeper
> than blue lines in agreement with the wavelength dependence of
> opacity, but some lines originate higher due to their excitation source

> **Comments:**
> **username_1**: @BenCrowell This figure refers to height of 650 km (where the H2 emissions have a maximum) See my edited answer  
> **username_1**: @uhoh See my edited answer  
> **username_0**: The paper is fascinating, excellent source! Since the original publication is open access I've added a direct link to it as well.  

---

