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I watched a CrashCourse video saying that nuclear fusion of $\rm H$ to $\rm He$ in the sun radiates mostly gamma rays. Then why are the lights that come to Earth comprise mainly of IR & visible ones?

Qmechanic
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longtry
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  • Does this answer your question? How is Earth protected from the gamma rays generated by the Sun? – John Rennie May 30 '23 at 09:03
  • IMHO, it's not a duplicate because OP wants to know why the peak of radiation which we receive is in the visible EM spectrum part (and not in other, shorter or longer wavelengths). – Agnius Vasiliauskas May 30 '23 at 09:07
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    But IS a duplicate of https://physics.stackexchange.com/questions/103987/light-formed-by-the-sun – ProfRob May 30 '23 at 22:15
  • Thank you 3. According to ProfRob's link, the claim that "It actually takes the average gamma ray photon about 170,000 years to diffuse out of the radiative zone" in an answer in John's link is absolutely wrong, because any gamma ray will be 'absorbed' within nanoseconds. But then why is the ratio of solar flux to that of a black body so low between 120 & 300nm, and so high when <100nm? https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spectrum_compared_to_black-body.gif – longtry May 31 '23 at 04:55
  • For $100nm$ part. Since it can't be the result of black body radiation of photosphere, I suspect it's mostly photons emitted from Solar transition region, where chromosphere transits to solar corona layer. $2000 km$ above sun atmosphere, there is some uniform of $2×10^4 K$ temperature zone which would have radiation peak at $145nm$. Not exactly a hard-UV $100nm$ peak given in black body discrepancy chart, but I think main reasons is that sun strictly speaking is not a black body. Black body just good approximates visible spectrum part. – Agnius Vasiliauskas May 31 '23 at 14:21

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