Re: [ATM] Extended Object Brightness

[David Whysong <dwhysong@physics.ucsb.edu>]

On Sat, 10 Apr 2004, Daniel Reinders wrote:

>My question was how to theoretically reconcile the well known hazard of
>looking at the sun through a scope with the idea (see archives under "More
>photons in my eye? ") that extended objects cannot be made brighter by
>passive means to the eye, due to exit pupil effects - unlike stars which are
>point sources.  Note that this is not true were one to place the eye at
>prime focus where it is clear that aperature does matter for extended
>objects.  Is this a case where a small "spot" of radiation heat flux can be
>tolerated very briefly (again NOT a recommendation to do so!) as per the
>naked eye case, but that same heat flux applied over the entire retina
>cannot be tolerated because it raises the "global" temperature of the
>eyeball more than the eye can stand (i.e. humours/retina get hot and cool
>down too slowly).  Is the answer here in the anatomy and pathophysiology of
>retinal burns, and not in the optics of extended objects?

I think it's more basic physics than anatomy or physiology. With a
telescope, the surface brightness of the sun may be diminished but the
total illuminated area on the retina is tremendously increased. The total
power going into your eye is also greatly increased. At zero power, the
image of the sun on the retina is fairly small so blood flow may cool the
affected area just enough to prevent substantial damage from brief
exposure.

--
David Whysong                                       dwhysong@physics.ucsb.edu
Astrophysics graduate student         University of California, Santa Barbara
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