<p>The Sun's corona is primarily composed of hydrogen and helium atoms, which are being impacted by sunlight. The electromagnetic frequencies vary quite a bit, and only a small portion of the frequencies are capable of exciting the helium atoms in the corona. In this <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ab9d84/pdf" rel="nofollow noreferrer">paper</a> I found a graph showing the specific frequencies required for helium excitation.</p>
<p><a href="https://i.sstatic.net/fzLZHTV6.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/fzLZHTV6.jpg" alt="Frequencies required to excite helium" /></a></p>
<p>However, I couldn't find any information on the specific percentage of sunlight that falls within the right frequency range to excite helium. The graphs I've seen so far only show the range of frequencies present in sunlight. The few that include percentages have ranges that are too broad to be useful, such as this chart:</p>
<p><a href="https://i.sstatic.net/oYa29eA4.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/oYa29eA4.jpg" alt="the suns electromagnetic spectrum" /></a></p>
<p>What percentage of sunlight is in the correct frequency range to excite helium?</p>

CC BY-SA 4.0
2024-09-25T19:12:29.937Z
@ScienceSnake I am mainly interested in the part of the corona which is around 10 million kilometers away from the surface of the sun. A quick google search tells me that the corona is at 2 million degrees Fahrenheit, 1.1 million Celsius https://www.nasa.gov/science-research/heliophysics/nasas-parker-solar-probe-and-the-curious-case-of-the-hot-corona/ and at around 10^15 particles per cubic meter https://en.wikipedia.org/wiki/Stellar_corona#Physics_of_the_corona I hope that helps
The Rocket fan
CC BY-SA 4.0
2024-09-25T20:52:23.503Z
The Sun's corona contains almost no atoms. It is ionised hydrogen and helium. The corona is optically thin and absorbs almost no light. The corona is not heated by absorbing light.
ProfRob
CC BY-SA 4.0
2024-09-25T21:07:56.803Z
10 million kilometers? You won't be able to see any spectral lines anymore that far out. Spectral lines are observed in the E-corona, which extends only up to about 1 million kilometers (see https://eclipse2017.nasa.gov/origin-corona%27s-light ). In any case, the corona is almost 100% ionized, so there are hardly any atoms in the ground state that could be excited. Excited atoms result practically only from recombination of electrons with ions into the corresponding levels.
Thomas
CC BY-SA 4.0
2024-09-26T03:51:10.190Z
@Thomas, thanks for the correction. In this case, I will change the value for the question from ten million to under one million. You can disregard the ten million kilometer value.
The Rocket fan
CC BY-SA 4.0
2024-09-27T07:06:24.480Z
Even at 1 million kilometers, at these temperatures excited atoms will result from recombination of ions and electrons rather than excitation from the ground state by sunlight.
Thomas
<electromagnetic-spectrum><helium><corona>
What percentage of the sunlight is in the right frequency to excite helium?
The Rocket fan
# What percentage of the sunlight is in the right frequency to excite helium?

(Asked by: username_0 on 2024-09-25)

The Sun's corona is primarily composed of hydrogen and helium atoms, which are being impacted by sunlight. The electromagnetic frequencies vary quite a bit, and only a small portion of the frequencies are capable of exciting the helium atoms in the corona. In this [paper](https://iopscience.iop.org/article/10.3847/1538-4357/ab9d84/pdf) I found a graph showing the specific frequencies required for helium excitation.

[![Frequencies required to excite helium](https://i.sstatic.net/fzLZHTV6.jpg)](https://i.sstatic.net/fzLZHTV6.jpg)

However, I couldn't find any information on the specific percentage of sunlight that falls within the right frequency range to excite helium. The graphs I've seen so far only show the range of frequencies present in sunlight. The few that include percentages have ranges that are too broad to be useful, such as this chart:

[![the suns electromagnetic spectrum](https://i.sstatic.net/oYa29eA4.jpg)](https://i.sstatic.net/oYa29eA4.jpg)

What percentage of sunlight is in the correct frequency range to excite helium?

**Tags:** electromagnetic-spectrum, helium, corona

> **Comments:**
> **username_0**: @ScienceSnake I am mainly interested in the part of the corona which is around 10 million kilometers away from the surface of the sun. A quick google search tells me that the corona is at 2 million degrees Fahrenheit, 1.1 million Celsius https://www.nasa.gov/science-research/heliophysics/nasas-parker-solar-probe-and-the-curious-case-of-the-hot-corona/ and at around 10^15 particles per cubic meter https://en.wikipedia.org/wiki/Stellar_corona#Physics_of_the_corona I hope that helps  
> **username_1**: The Sun's corona contains almost no atoms. It is ionised hydrogen and helium. The corona is optically thin and absorbs almost no light. The corona is not heated by absorbing light.  
> **username_2**: 10 million kilometers? You won't be able to see any spectral lines anymore that far out. Spectral lines are observed in the E-corona, which extends only up to about 1 million kilometers (see https://eclipse2017.nasa.gov/origin-corona%27s-light ). In any case, the corona is almost 100% ionized, so there are hardly any atoms in the ground state that could be excited. Excited atoms result practically only from recombination of electrons with ions into the corresponding levels.  
> **username_0**: @username_2, thanks for the correction. In this case, I will change the value for the question from ten million to under one million. You can disregard the ten million kilometer value.  
> **username_2**: Even at 1 million kilometers, at these temperatures excited atoms will result from recombination of ions and electrons rather than excitation from the ground state by sunlight.  

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## 0 answers

