<blockquote>
<p>How has knowledge of fusion of the Sun changed astronomy?</p>
</blockquote>
<p>TL;DR: It changed <strong>everything</strong>.</p>
<p>Up until the 1930s, physicists and astronomers argued for a rather young universe while geologists and biologists argued for a markedly older Earth. The problem was that physicists and astronomers couldn't image any known processes that would possibly allow the Earth to be as old as geologists and biologists claimed. Note well: geologists and biologists of that time were not arguing for an Earth that is 4.55 billion years old. They were wanting an Earth that was at least several hundred million years old.</p>
<p>Hans Bethe's 1938 paper, along with a few papers that immediately preceded Bethe's paper, paved the way for addressing that discrepancy. It wasn't until the 1950s when Clair Cameron Patterson showed that the Earth was much older than geologists and biologists thought. The 1950s also were when the apparently ridiculous claims of an expanding universe finally become accepted.</p>

CC BY-SA 4.0
2021-03-24T07:28:07.363Z
I once met Hans Bethe after he gave a colloquium on this (ca. 1990+/-?) back when transparencies and overhead projectors were the norm. I so wanted to ask him if I could have the one with the light nuclei fusion reactions written on it, but was too shy to ask.
uhoh
CC BY-SA 4.0
2021-03-24T08:45:12.173Z
The original paper by Hans Bethe is a very fine read and a good example how to write concise and well understandably, nothing hidden behind phrases.
planetmaker
CC BY-SA 4.0
2021-03-24T16:24:06.080Z
Arguably, though, you could say that Astronomy didn't really gain significant, serious scientific traction until Hubble and the Hooker telescope - this effectively concurrent with discoveries relating to fusion in the sun.  One might argue that it didn't so much *change* anything, per se, since these two branches of science sort of grew up together.  Neither field was mature enough to suffer a major shift because of the other - they sort of co-evolved together.  There wasn't a lot of *old* astronomical data that suddenly could be re-interpreted, for example.  It was more synergistic.
J...
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2021-03-24T19:45:17.817Z
This answer nails it. "Everything"
Stilez
CC BY-SA 4.0
2021-03-25T04:22:50.397Z
What is the title of this 1938 article by Hans Bethe? I’d love to read it!
Pierre Paquette
CC BY-SA 4.0
2021-03-25T04:46:01.143Z
@PierrePaquette What you probably want to read is his 1939 article, [Energy Production in Stars](https://journals.aps.org/pr/abstract/10.1103/PhysRev.55.434). At least for now, you can simply click the PDF button at that link to be able to read the full text.
David Hammen
CC BY-SA 4.0
2021-03-25T08:17:13.157Z
@J... You're right, very arguable. Since most European monarchs sponsored astronomy and astronomers, even in the 17th century. Astronomy was perhaps the most important science in the Renaissance.
ProfRob
CC BY-SA 4.0
2021-03-25T09:57:03.160Z
@ProfRob Regardless, it was in its infancy.  At the time it was little more than a game of marbles that people amused themselves with making predictions about.  It was Newtonian mechanics put to play - mostly geometry and mechanics.  At the turn of the 20th century astronomy was more concerned with the orbit of Mercury than the innards of the Sun. The biggest outstanding observation in astronomy was arguably Fraunhofer's, and that was resolved not with an understanding of fusion, but rather the atom's electronic structure, the photoelectric effect, etc.
J...
CC BY-SA 4.0
2021-03-25T09:59:48.407Z
@ProfRob We didn't discover pulsars until 1967.  We were just starting to make observations of supernovae in the 1920s.  Unlike the discovery of bacteria, which did revolutionize medicine, for example, because it finally explained a long series of observations whose fundamental causes had previously eluded us, astronomy had not yet made sufficiently detailed observations of the universe to *require* an understanding of fusion to explain them.  Those observations mostly came concurrent with or after an understanding of the nucleus.
J...
CC BY-SA 4.0
2021-03-25T10:57:45.960Z
@J... The concepts advanced by Hubble and Lemaître weren't taken seriously until the serendipitous discovery of the cosmic microwave background radiation in 1964. Up until then, their concepts were disparagingly referred to as the "big bang theory". On the other hand, Bethe's work was taken seriously pretty much from the start.
David Hammen
CC BY-SA 4.0
2021-03-25T11:00:07.627Z
@DavidHammen Indeed.  Astronomy wasn't waiting around for nuclear physics to catch up - quite my point.  It was waiting for better astronomical tools to make better observations with.  +1 in any case, because the answer is good and relevant.  I'm just playing devil's advocate here to some degree.
J...
CC BY-SA 4.0
2021-03-24T05:41:26.307Z
2021-03-25T09:34:11.280Z
2021-03-25T09:34:11.280Z
David Hammen
<p><strong><a href="https://en.wikipedia.org/wiki/Solar_neutrino_problem" rel="nofollow noreferrer">Solar neutrino problem</a></strong></p>
<p>In the early experiments looking at the neutrino flux coming from the Sun, it was found that there where significantly fewer electron neutrinos than expected. One answer to that problem could have been that we did not understand the nuclear fusion inside the Sun and that there was less nuclear burning
inside the Sun producing less neutrinos. However, given that the Sun is shining (and our confidence in the knowledge of nuclear fusion inside the Sun) people needed to look elsewhere for a solution. Which leads to the theory of <a href="https://en.wikipedia.org/wiki/Neutrino_oscillation" rel="nofollow noreferrer">neutrino oscillations</a> and neutrinos having mass, where some the neutrinos produced inside the Sun change their &quot;flavor&quot; and thus become undetectable (or at least you need a different experiment to detect them). This is a  huge theoretical (and technical achievement to take the measurements) breakthrough and a change in our understanding of the standard model of physics.</p>

CC BY-SA 4.0
2021-03-24T11:27:21.497Z
2021-03-24T11:27:21.497Z
Rob
<p>I would like to know how knowledge of the fusion in the Sun has changed how astronomers explore the universe. What do astronomers do differently now that we know that the Sun’s use of proton-to-proton chain to create energy? Please include sources.</p>

CC BY-SA 4.0
2021-03-24T05:14:38.530Z
I think this question might be too broad for a Stack Exchange question. It feel to me to be asking for an essay or book-chapter, or at least a very long list. Can you narrow this down to something more specific and describe what research you have done so far? That way people will have a better idea of exactly what to focus on in an answer and how to avoid duplicating any work you've done already. *Thanks!*
uhoh
CC BY-SA 4.0
2021-03-24T08:44:10.680Z
It reads to me like a homework question. Please also remember to quote your sources (e.g. the people with the anwers) if you excerpt those :)
planetmaker
CC BY-SA 4.0
2021-03-24T09:03:02.173Z
Might be a better fit for [hsm.se] but I think it is on topic here (?).
StephenG - Help Ukraine
CC BY-SA 4.0
2021-03-24T09:36:44.427Z
There is a whole field called "Nuclear Astrophysics".
ProfRob
CC BY-SA 4.0
2021-03-24T23:00:46.417Z
@uhoh What do astronomers do different now that they know about fusion in the Sun?
Jackson
CC BY-SA 4.0
2021-03-24T23:08:37.477Z
@Jackson what do mathematicians do differently now that they know the square root of -1?
uhoh
CC BY-SA 4.0
2021-03-25T03:33:27.847Z
Scientists developed an understanding of nuclear physics, modelled this for the Sun's properties, compared this with observations, and compared all this with what we understood and modelled and observed for other stars and in nuclear tests and within laboratories and particle accelerators. What part of this complex and evolving understanding do you want to focus on? Is what astronomers "do" based on what they *know*, or advances in *theory*, or what *technology* is available to test their predictions – or all of these?
Chappo Hasn't Forgotten
<the-sun>
What do astronomers do different now that they know about fusion of the Sun?
Jackson
# What do astronomers do different now that they know about fusion of the Sun?

(Asked by: username_0 on 2021-03-24)

I would like to know how knowledge of the fusion in the Sun has changed how astronomers explore the universe. What do astronomers do differently now that we know that the Sun’s use of proton-to-proton chain to create energy? Please include sources.

**Tags:** the-sun
> **Comments:**
> **username_1**: I think this question might be too broad for a Stack Exchange question. It feel to me to be asking for an essay or book-chapter, or at least a very long list. Can you narrow this down to something more specific and describe what research you have done so far? That way people will have a better idea of exactly what to focus on in an answer and how to avoid duplicating any work you've done already. *Thanks!*  
> **username_2**: It reads to me like a homework question. Please also remember to quote your sources (e.g. the people with the anwers) if you excerpt those :)  
> **username_3**: Might be a better fit for [hsm.se] but I think it is on topic here (?).  
> **username_4**: There is a whole field called "Nuclear Astrophysics".  
> **username_0**: @uhoh What do astronomers do different now that they know about fusion in the Sun?  
> **username_1**: @Jackson what do mathematicians do differently now that they know the square root of -1?  
> **username_5**: Scientists developed an understanding of nuclear physics, modelled this for the Sun's properties, compared this with observations, and compared all this with what we understood and modelled and observed for other stars and in nuclear tests and within laboratories and particle accelerators. What part of this complex and evolving understanding do you want to focus on? Is what astronomers "do" based on what they *know*, or advances in *theory*, or what *technology* is available to test their predictions – or all of these?  

---

## 2 answers

### Answer by username_6 on 2021-03-24. Score: 25

> How has knowledge of fusion of the Sun changed astronomy?

TL;DR: It changed **everything**.

Up until the 1930s, physicists and astronomers argued for a rather young universe while geologists and biologists argued for a markedly older Earth. The problem was that physicists and astronomers couldn't image any known processes that would possibly allow the Earth to be as old as geologists and biologists claimed. Note well: geologists and biologists of that time were not arguing for an Earth that is 4.55 billion years old. They were wanting an Earth that was at least several hundred million years old.

Hans Bethe's 1938 paper, along with a few papers that immediately preceded Bethe's paper, paved the way for addressing that discrepancy. It wasn't until the 1950s when Clair Cameron Patterson showed that the Earth was much older than geologists and biologists thought. The 1950s also were when the apparently ridiculous claims of an expanding universe finally become accepted.

> **Comments:**
> **username_1**: I once met Hans Bethe after he gave a colloquium on this (ca. 1990+/-?) back when transparencies and overhead projectors were the norm. I so wanted to ask him if I could have the one with the light nuclei fusion reactions written on it, but was too shy to ask.  
> **username_2**: The original paper by Hans Bethe is a very fine read and a good example how to write concise and well understandably, nothing hidden behind phrases.  
> **username_7**: Arguably, though, you could say that Astronomy didn't really gain significant, serious scientific traction until Hubble and the Hooker telescope - this effectively concurrent with discoveries relating to fusion in the sun.  One might argue that it didn't so much *change* anything, per se, since these two branches of science sort of grew up together.  Neither field was mature enough to suffer a major shift because of the other - they sort of co-evolved together.  There wasn't a lot of *old* astronomical data that suddenly could be re-interpreted, for example.  It was more synergistic.  
> **username_8**: This answer nails it. "Everything"  
> **username_9**: What is the title of this 1938 article by Hans Bethe? I’d love to read it!  
> **username_6**: @PierrePaquette What you probably want to read is his 1939 article, [Energy Production in Stars](https://journals.aps.org/pr/abstract/10.1103/PhysRev.55.434). At least for now, you can simply click the PDF button at that link to be able to read the full text.  
> **username_4**: @J... You're right, very arguable. Since most European monarchs sponsored astronomy and astronomers, even in the 17th century. Astronomy was perhaps the most important science in the Renaissance.  
> **username_7**: @ProfRob Regardless, it was in its infancy.  At the time it was little more than a game of marbles that people amused themselves with making predictions about.  It was Newtonian mechanics put to play - mostly geometry and mechanics.  At the turn of the 20th century astronomy was more concerned with the orbit of Mercury than the innards of the Sun. The biggest outstanding observation in astronomy was arguably Fraunhofer's, and that was resolved not with an understanding of fusion, but rather the atom's electronic structure, the photoelectric effect, etc.  
> **username_7**: @ProfRob We didn't discover pulsars until 1967.  We were just starting to make observations of supernovae in the 1920s.  Unlike the discovery of bacteria, which did revolutionize medicine, for example, because it finally explained a long series of observations whose fundamental causes had previously eluded us, astronomy had not yet made sufficiently detailed observations of the universe to *require* an understanding of fusion to explain them.  Those observations mostly came concurrent with or after an understanding of the nucleus.  
> **username_6**: @J... The concepts advanced by Hubble and Lemaître weren't taken seriously until the serendipitous discovery of the cosmic microwave background radiation in 1964. Up until then, their concepts were disparagingly referred to as the "big bang theory". On the other hand, Bethe's work was taken seriously pretty much from the start.  
> **username_7**: @DavidHammen Indeed.  Astronomy wasn't waiting around for nuclear physics to catch up - quite my point.  It was waiting for better astronomical tools to make better observations with.  +1 in any case, because the answer is good and relevant.  I'm just playing devil's advocate here to some degree.  

---

### Answer by username_10 on 2021-03-24. Score: 2

**[Solar neutrino problem](https://en.wikipedia.org/wiki/Solar_neutrino_problem)**

In the early experiments looking at the neutrino flux coming from the Sun, it was found that there where significantly fewer electron neutrinos than expected. One answer to that problem could have been that we did not understand the nuclear fusion inside the Sun and that there was less nuclear burning
inside the Sun producing less neutrinos. However, given that the Sun is shining (and our confidence in the knowledge of nuclear fusion inside the Sun) people needed to look elsewhere for a solution. Which leads to the theory of [neutrino oscillations](https://en.wikipedia.org/wiki/Neutrino_oscillation) and neutrinos having mass, where some the neutrinos produced inside the Sun change their "flavor" and thus become undetectable (or at least you need a different experiment to detect them). This is a huge theoretical (and technical achievement to take the measurements) breakthrough and a change in our understanding of the standard model of physics.


---

