Subject: Colors
Date: Fri, 22 Jan 1999 11:43:47 -0500 (EST)
From: "Deborah A. DeMania" <dad3w@unix.mail.virginia.edu>
To: rfosbury@eso.org

Hello!

I just stumbled upon your homepage today, and I'm hoping you can solve a
mystery for me.

I'm a graduate student in Materials Science at the University of Virginia.
Recently, on a particularly clear day, our Crystallography professor
commented on how blue the sky was.  It initiated a lively discussion about
"why is the sky blue".  After our mini-scattering lesson, we concluded
that the blue light was scattered more than the other wavelengths (why?),
and that during sunset, when the sunlight must travel through a thicker
portion of the atmosphere, the longer wavelengths are scattered instead
(why?).  My question, a few months after the fact on an equally clear day
was, if that is so, then why isn't there a time when a portion of the sky
looks green as the sun is decending???  A friend of mine said, well, there
IS green there, it's just very faint.  Hm.  I don't think so.

Is the green wavelenth absorbed somehow?  Or is the scattering phenomenon
not really the full explaination for why sunsets are red?  And why is it
that the higher energy (blue) wavelenths are scattered more for a thinner
section of atmosphere, but lower energy (red) for a thicker section?

Sorry if this reveals my total ignorance of basic physics questions that I
should have learned many years ago, but no one I've asked so far has been
able to give me an answer.

I had hoped that your "sky" page would explain all of this, but apparently
it is under construction.  I'm hoping that you'll be able to give me a
preview.

Thanks in advance!
Cheers,
Deborah

Deborah A. DeMania
MSB 211
Materials Science and Engineering Department
University of Virginia
Charlottesville, VA  22906

phone: (804)-982-5691
email: dad3w@virginia.edu