Re: change of airmass, change of time, redundancy

[hjohnson@pluto.njcc.com (Herbert R Johnson)]

Chris argues in reply to me that the effects of airmass, and other
atmospheric considerations, are important; and so reporting a single
"airmass" value is good and sufficient. An azimuth angle can be
computed, he says, from other camera and image information.

I have suggested that by reporting the camera's azimuth, one gets
a direct quantity; that one can otherwise use their or other's considerations
of the atmosphere to compute their own value.

Chris also argues that a camera's date/time of exposure and its location
CAN be found reliably; therefore the reports of such ARE reliable. I've
suggested these are subject to error and therefore redundant data like
azimuth is a good idea and diagnostic. I will not embarass my colleagues
by mentioning examples where Mark III data had incorrect time stamps;
my point is that errors or equipment faults can occur, so some redundant
data can find them and possibly correct for them.

Arne also comments upon these issues again in brief. He suggests reporting
a value for airmass is reasonable, and suggests avoiding what I'd call
"outright" redundancy by reporting the same value multiple times. With the
latter I certainly agree; and reporting an airmass value per se is fine,
if it is well-defined process one can work backward (or use image geometry) to
determine azimuth and recompute another value based on different assumptions.

Herb Johnson

Herbert R. Johnson              http://pluto.njcc.com/~hjohnson
hjohnson@pluto.njcc.com         voice 609-771-1503, New Jersey USA
             amateur astronomer and astro-tour guide
           S-100 computer parts, manuals as "Dr. S-100"
    reseller of 68K Macs & accessories for your computing pleasure