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Name: Justin
Status: educator
Grade: other
Location: N/A
Country: N/A
Date: 11/7/2005


Question:
The Sun produces a continuous spectra. Why is it not just many many spectral lines from the many many electron 'jumps' possible in the different atoms?


Replies:
Your first premise is incorrect; however, that does not minimize your insight that there "should be" absorptions in the continuous Solar blackbody radiation. The Sun does NOT produce a continuous spectrum of electromagnetic radiation. Under high resolution there are many "holes" in the continuum due to absorptions of atoms and molecules in the solar atmosphere. The same is true of other stars also. And of course absorptions due to molecules in the Earth's atmosphere if the telescope is land-based. While these are only observable with a high resolution spectrometer, astronomers use these spectra to gain a lot of information about the Sun and stars. For example, comparing the shift in wavelength from the results obtained in terrestrial laboratories (the Doppler shift) it is possible to infer the speed at which the star is moving radially away from the Earth, and from experiments relating the brightness, and speed of recession it is possible to estimate the distance of the source (the Hubble correlation). The first of the two web sites below is especially interesting because you can "dial" a wavelength range and obtain either a picture of the absorption lines or a table of the values of the absorptions. One note: the wavelengths are reported in Angstroms, not nanometers, (1 Ang = 10 nm) so multiply nanometers by (10x).

http://bass2000.obspm.fr/solar_spect.php>

http://www.ccpo.odu.edu/SEES/ozone/class/Chap_4/4_2.htm

Vince Calder



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