Science Questions

Sat, 15th Jul 2006

Part of the show Sun Tans, Fission and Fusion

Question

Alan in Worcestershire asked:

I know that there is a wide range of frequencies in the electromagnetic radiation that comes from the sun. But exactly how many discrete frequencies are there, and what determines the frequency radiated?

Answer

The light that comes from the Sun would be in a continuous spectrum and it's dictated by the temperature of the Sun. The colour tells you what temperature it is. From the Sun's photosphere, the rays of light go from x-rays through visible light all the way up to radiowaves, but they peak at around 550nm, which is red light. It peaks in the visible part of the spectrum. That would be continuous were it not for the fact that there are discrete energies that are absorbed and emitted by the different atomic species on the Sun. For example, the element helium was discovered by astronomers noticing that there was a gap in the spectrum that corresponded to an element that they previously didn't know about. So they called it helium after the Greek god Helios.

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