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Re: Tropical LMs? (was Re: (meteorobs) Re: Zodiacal light)
On Wed, 2 Feb 2000, Jim Bedient wrote:
> At 05:18 PM 2/2/00 -0500, Lew wrote:
> >
> >Jim, how do your LMs from Haleakala and Mauna Kea compare with those you
> >were used to recording from the very darkest sites on the mainland before?
> >
My experience that the LMs at the darkest mainline sites are comparable.
For instance, Sutherland in the Karoo desert compares favourably with
Mauna Kea at 6400' and 9400'.
> They are pretty comparable. I have always wondered at this too, but not
> enough to really research it! In Hawaii, I have always typically observed
> at sea level, or close to it, and attributed any less-than-ideal conditions
It's generally too cloudy for me to do that. I have seen to +6.7 in
Hilo in a dry period, but it's normally a half a mag worse than that.
Looking north into town, the LM goes off rapidly, so hunting for
possible Linearids was a non-starter for me.
> Molokai, at a few hundred feet above sea level. On Haleakala or Mauna Kea,
> you get above a bunch of the atmosphere, and particularly on Mauna Kea
> above the moisture (which is why the observatories are there to begin
> with), but there are oxygen deprivation effects that begin to rob you of
> night vision. I don't know that those physiological effects have ever been
> quantified, but they would certainly have an effect on observer-perceived
> LM.
I can't that I've noticed the oxygen deprivation for general working or
affecting the LM. At the summit the LM is worse than lower down, but
that's after only a few minutes' dark adaption after coming out of an
illuminated control room. Sometime I must take up a sleeping bag and do
a comparison. For me the skies at 9400' and 6400' (if the cloud has
gone from the Saddle road, can be as good as anywhere else I've seen.
The skies do look bright yet the LM is wonderful. The various zodiacal
phenomena recently discussed can all (except perhaps for L5) be seen.
I agree with earlier remarks about pollutants. These make a big
difference to the LM and apparent brightness of the sky.
Malcolm
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