wcs.ps and scs.ps

[Mike Nolan]

>      I am unfamiliar with airmass, does it have a clear definition?

Airmass is atmospheric optical depth normalized to zenith optical depth
assuming a spherically uniform atmosphere.  It is usually
approximated as sec(zenith angle), which is the only other case
(besides sin za) I can think of that needs explicit trig.  One
generally measures extinction as a function of airmass for calibration
of optical photometry.

I don't have any idea why one would need inverse trig functions, I
only wanted to note that they are one of the cases where you'd rather
choose the notation in advance.

-Mike

---------------------------
Mike Nolan <nolan at naic.edu>
+1 787 878 2612 Home: +1 787 895 6746 Fax: +1 787 878 1861
Arecibo Observatory / Cornell University
HC03 Box 53995, Arecibo, Puerto Rico 00612