I forgot to say thanks you to nstahl and Rob for explaining the difference in size between the Earth's surface and the Sun's. Rob, thank you for your traditionally coloured large "sueare of a Sun" compared with the tiny blue dot of the Earth!
And thank you, nstahl, for your compliment!
Art, you said something that I somehow missed the first time I read it:
The sun is indeed a wideband photospheric light source with the exception
of numerous narrow dark chromospheric Fraunhofer lines including the red 656.281nm Hα line.
While the (~5800 K) photosphere also radiates red 656.281nm Hα line that photospheric radiation
is all absorbed by the chromosphere which then re-radiates its own red 656.281nm Hα line
in accordance with its own (mostly colder ~ 4500K) temperatures.
It is only these colder darker chromospheric Fraunhofer lines that we can observe.
How interesting! Does that mean that the Ha radiation at 656.281nm that the chromosphere receives from the photosphere and then re-radiates is longer than 656.281nm? And if not, why not? I thought that is how it works. A hydrogen atom receives an ultraviolet photon from a hot surface (typically an O- or B-type sun) and re-radiates that energy as a red 656.281nm photon. Or an oxygen atom receives an even "harder" ultraviolet photon from a very hot source, say the central star of a planetary nebula, and re-radiates it as a photon whose wavelength is about 502 nm.
Therefore, if the chromosphere receives 656.281nm photons from the photosphere, shouldn't it re-radiate this energy at even longer wavelengths, probably in the infrared part of the spectrum?
Or maybe the chromosphere doesn't re-radiate the Ha light from the photosphere at all, but rather the chromosphere is inonized by ultraviolet light from the photosphere and re-radiates this ultraviolet light as its own 656.281nm photons?
Now that makes a lot more sense.
Ann
Ann
I forgot to say thanks you to nstahl and Rob for explaining the difference in size between the Earth's surface and the Sun's. Rob, thank you for your traditionally coloured large "sueare of a Sun" compared with the tiny blue dot of the Earth!
And thank you, nstahl, for your compliment!
Art, you said something that I somehow missed the first time I read it:
[quote]The sun is indeed a wideband photospheric light source with the exception
of numerous narrow dark chromospheric Fraunhofer lines including the red 656.281nm Hα line.
While the (~5800 K) photosphere also radiates red 656.281nm Hα line that photospheric radiation
is all absorbed by the chromosphere which then re-radiates its own red 656.281nm Hα line
in accordance with its own (mostly colder ~ 4500K) temperatures.
It is only these colder darker chromospheric Fraunhofer lines that we can observe.[/quote]
How interesting! Does that mean that the Ha radiation at 656.281nm that the chromosphere receives from the photosphere and then re-radiates is longer than 656.281nm? And if not, why not? I thought that is how it works. A hydrogen atom receives an ultraviolet photon from a hot surface (typically an O- or B-type sun) and re-radiates that energy as a red 656.281nm photon. Or an oxygen atom receives an even "harder" ultraviolet photon from a very hot source, say the central star of a planetary nebula, and re-radiates it as a photon whose wavelength is about 502 nm.
Therefore, if the chromosphere receives 656.281nm photons from the photosphere, shouldn't it re-radiate this energy at even longer wavelengths, probably in the infrared part of the spectrum?
Or maybe the chromosphere doesn't re-radiate the Ha light from the photosphere at all, but rather the chromosphere is inonized by ultraviolet light from the photosphere and re-radiates this ultraviolet light as its own 656.281nm photons?
Now that makes a lot more sense.
Ann
Ann