Re: Astro Trip and human limiting mag as a function of altitude

Richard Ozer notes:

I know a group of people who go up to Barcroft every year and rave about the
> transparency and darkness.
>

while Mark Jounson writes:

As far as visual observing conditions I believe over 12000 feet is not the
> best of sites. The lower oxygen levels actually will lower your own naked
> eye visual limiting magnitude ... Backyard Astronomer's Guide claims the
> limiting mag at the 14000 foot Mauna Kea site is worse than the 9000 foot
> level of that same mountain
>

I have overnighted above 18,000 feet in South America more than once, and
have camped at over 14,000 for weeks and done visual astronomy.

I believe that the above two quotations, together, correctly describe the
situation.

Indeed it is "darK' at Barcroft. The Milky Way stands out in beautiful
contrast to the dark sky background. ... And one should be suspicious: is
it that the Milky Way is extra-bright or that the background is a bit too
dark?

At high altitude, even when you are adapt for a long time, the sky
background appears darker than it would if you were at lower altitude -- or
took a hit from an oxygen source(*).

I can get the same effect at Willow Springs on a good night: Well-adapted, I
note the appearance of the Milky Way. Then I use some head-lamp
illumination putting telescope gear back into the container. Then I look at
the sky again before leaving: the Milky Way is better-appearing that it was!
 Because I dis-adapted my eyes a bit and the "sky background" is darker.

Bob Ayers

(*) I hear that this is a ritual at the observatories on Mana Kea.

---
GSSP registration deadline - June 12th: http://www.goldenstatestarparty.blogspot.com
June 8, 2009: TAC Web Page Updated http://observers.org/TAC.cgi/Announcements/
TAC mailing list - to join, manage, or leave: http://nine.pairlist.net/mailman/listinfo/tac