[little pixie]

I was reading an astronomy textbook and it states

In the UV at 2200A the absorption peaks due to carbon bonds.

and

Spectra of visible gas clouds show strong emission lines due to Hydrogen, particularly H at lambda = 6545A.

Though the 'A' is not as I have typed it, but instead has a small circle attached to the top of it. I was wondering what these 'A' units are, and what this 'A' symbol is?

Thank you.

[Stonebridge]

It's Å and stands for Ångström units.

One Å is 10^-10m or 0.1nm and is commonly used in spectroscopy.
It's named after a Swedish physicist.

Info here
http://en.wikipedia.org/wiki/Angstrom

Btw. Å (å) is the 27th letter in the Swedish alphabet.

[little pixie]

Thanks very much Stonebridge!