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jordankonisky
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I understand that the fusion of hydrogen to helium in our sun's core generates gamma rays. My question is how are these gamma rays transformed to the full spectrum of photons that we that we observe from earth?
jordankonisky said:I understand that the fusion of hydrogen to helium in our sun's core generates gamma rays. My question is how are these gamma rays transformed to the full spectrum of photons that we that we observe from earth?
You're thinking of the upper layers of the photosphere, which get cooler since temperature drops as the light diffuses out. But once you get to a low enough density that the light just streams out, there is no longer any need for the temperature to continue to drop, and in fact what actually happens (kind of like in the Earth's atmosphere) is the temperature starts to rise again. So the chromosphere is actually hotter than the photosphere, and tends to produce emission rather than absorption.drvrm said:Outside of the photosphere is a more diffuse, cooler ( at 4500K) level known as the Chromosphere. Atoms within the chromosphere absorb some of the photons, causing absorption lines (Dark lines) in the solar spectrum.
Ken G said:So the chromosphere is actually hotter than the photosphere, and tends to produce emission rather than absorption.
Indeed, in fact it depends a lot on how one defines the chromosphere. It seems the Wiki is using the definition of everything above the optical depth of 2/3 point, which is what some call the "photosphere" because it is the average depth of last emission of sunlight. That's not a very physically relevant definition, however-- it treats the "photosphere" as if it was the surface of a sphere, but the "chromosphere" is a spherical shell of finite thickness-- not very consistent terminology. Instead, a more meaningful definition is to look at the physics, and call the "photosphere" the region where the energy equation is dominated by radiative diffusion of sunlight (so, above the convection zone), and the "chromosphere" the region where the energy equation is dominated by mechanical heating (be it wave or magnetic heating) and radiative cooling from lines. The crossover between those types of physics occurs as the density drops and the gas becomes very easy to heat mechanically rather than by absorption of photons, but the mechanical heating also produces what is called a "temperature inversion" similar to what we see in Earth's atmosphere. Indeed, an alternative less physical but pretty simple definition of the chromosphere is everything above the temperature minimum. That definition would mean that the chromosphere starts out rather cool, but very rapidly gets much hotter as you go up. In any event, the chromosphere is characterized by being hot, rather than by being cool.DrSteve said:The temperature profile of the chromosphere is non-trivial.
In astronomy, "radiation" almost always means just plain light (not necessarily visible light), as it does here.my2cts said:Within 3/4 of the solar radius energy is transported out by radiation.
Not being an expert, I would expect this radiation to be in the form plasma waves.
Ken G said:It's one of the amazing thing about thermal physics, there are a lot of situations where the behavior you see is just the most likely given the energy constraints-- the details don't matter. You can think of it as a kind of general case of the central limit theorem, wherein you can expect a certain type of distribution (in that case, Gaussian instead of Planckian) simply because it is the one that happens in the most ways, so it is the most likely-- regardless of the details of the system that is creating it. So just like if I looked at the height of a random collection of people at a given age, I expect a Gaussian distribution even if I know nothing of the physics of growing or the biology of DNA, similarly you can expect a Planckian radiation field coming from a "blackbody" (a system that interacts strongly with light) at a given temperature, regardless of the details of what the system is made of or how it actually does interact with light.
jordankonisky said:I just don't understand how physically the full spectrum of photon energy at each temperature would be generated?
Thanks do much for the clear explanation.drvrm said:i think when one looks up the 'wien's distribution' its an emperical formulation on the basis of observations of intensity distribution of a 'black-body' and for theoretical understanding we go to the Planck's radiation law based on oscillators...suppose one artificially arranges some particles at some thermal state ...the whole spectrum may not be generated ...just logically the emission mechanism must be there for the radiation to come out and contribute...one should employ simple logic ...
The full solar spectrum can be derived by analyzing the energy levels and wavelengths of the different types of radiation emitted by the sun. This includes not only gamma rays, but also x-rays, ultraviolet light, visible light, infrared radiation, and radio waves. By measuring and plotting the intensity of each type of radiation, we can create a full spectrum that shows the range of energies and wavelengths present in the sun's radiation.
To accurately measure and analyze the full solar spectrum, scientists use a variety of instruments including spectrometers, telescopes, and detectors. These instruments are designed to detect and measure different types of radiation, and are often used in combination to provide a complete picture of the sun's spectrum.
Deriving the full solar spectrum is crucial for understanding the physical processes that occur in the sun and for studying the effects of solar radiation on Earth. It also allows us to better understand the composition and structure of the sun, as well as to make predictions about solar activity and potential impacts on our planet.
Yes, the full solar spectrum can change over time due to fluctuations in the sun's activity and changes in its composition. For example, during periods of increased solar activity, the intensity of certain types of radiation may be higher, resulting in a slightly different spectrum. Additionally, changes in the sun's magnetic field and the presence of sunspots can also affect the full solar spectrum.
The data from the full solar spectrum is used in a wide range of scientific research, including solar physics, atmospheric science, and climate studies. By analyzing the different components of the solar spectrum, scientists can learn more about the sun's energy output, the effects of solar radiation on Earth's atmosphere, and how the sun's activity impacts our climate. This information is also important for developing technologies and strategies to mitigate potential risks associated with solar flares and other solar events.