(IAAC) Limiting mag. and personal equation: Another Component

Dear Lew and Steve,

Another factor which should be taken into account is the level of
oxygen saturation of the observer's retina.

A few years ago, a friend and I were observing from the 10,000' [3050
meter] level of Mount Graham, Arizona. We had brought a medical oxygen
tank and mask, to experiment with.

For the first half of the evening it seemed to have no perceptible
effect, in several uses for varying lengths of time. So we continued
observing without it, to preserve what oxygen we had.

In the wee hours, however -- around 3:00 am -- the cumulative effect of
time spent observing at altitude caught up with me. My eyes were so
tired that, with the unaided eye, all the stars looked like blurry
disks. It looked like it was time to call it a night.

But then, out of curiosity, I tried the oxygen mask one last time.
Magic! Within seconds, the stars were razor-sharp again. I was able to
continue observing for the rest of the night.

Clear skies,


Thomas O'Hara, PhD
San Diego, California, USA

"Puritanism is the haunting fear that
Someone, somewhere, may be happy."
                     --H. L. Mencken
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