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Name: John Y.
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 2001-2002

Why does sun light give continuous spectrum? Does the source of sun light not originate from energy transfer between orbitals of different energy level?

Hi, John

As you know, the nucleus of the Sun has a temperature of about 15.000.000 Kelvin. Under such conditions, the atoms hit each other and may fusion into other new and heavier nucleus, in a thermo-nuclear reaction. During such process, some mass is "lost" and - according to Einstein - E=m.c^2 what means mass generate energy. Part of this energy travels as electromagnetic waves, with all wave lenghts, and that is why the spectrum of the sunlight is continuous, from the nucleus. Furthermore, reaching the sun surface, where the temperature is "lower", part of this energy is absorbed by several elements that - in turn - promote electrons to higher energy levels. And that is why you get dark strips over the continuous sun spectrum (the so called "Fraunhoffer Dark Lines").

Best regards

Alcir Grohmann

The sun, obviously, is a hot body. Hot bodies emit radiation with a spectral distribution given by the Planck formula -- so called black body radiation that is continuous for all practical purposes. The radiation, in principle, is discrete however the emissions are broadened by the pressure of the gases comprising the Sun and the specific emissions are so close together and numerous that they cannot be resolved experimentally.

There are discrete absorption lines in the solar spectrum due to absorptions of specific wavelengths of cooler gases in the sun's outer atmosphere -- called Fraunhofer lines. The element helium was first discovered from its absorptions in the solar spectra.

Vince Calder

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