Understanding Spectral Index: A Plain Explanation

[Sanjay87]

Hi,

Can anybody please explain to me (in everyday language) what spectral index is? The wikipedia entry doesn't shed much light, and a lot of the textbooks give very convoluted explanations for its derivation.

Thanks.

 

[matt.o]

In radio terms (in my experience), spectral index applies to synchrotron sources which have brightness, S, which changes with for different frequencies, $$\nu$$, such that $$S \propto \nu^{\alpha}$$. For a negative $$\alpha$$ this means that when a synchrotron source is observed at higher frequencies, it will be fainter. The opposite is true for positive $$\alpha$$.