It’s Friday afternoon and time for a mildly frivolous post.

I’ve been recently been teaching first-year astrophysics students (and others) about the radiation emitted by stars, and how stellar spectra can be used to diagnose their physical properties.

Received wisdom is that the continuous spectrum of light emitted by stars like the Sun is roughly of black-body form, with a peak wavelength inversely proportional to the surface temperature of the star. Here are some examples of black-body curves to illustrate the point.

The Sun has a surface temperature of about 6000 K – actually, more like 5800 K but we won’t quibble. The peak wavelength for the Sun’s spectrum therefore corresponds to bluey-green light, which is why the Sun appears … er… yellow.

Anyone care to offer an explanation as to why the Sun isn’t green? Answers on a postcard or, preferably, through the comments box.

And while you’re at it, you might want to comment on why, if the Sun produces so much green light, chlorophyll is actually green?



