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Re: (meteorobs) More on LM estimates and sources of error in ZHRs
Thanks for answering this one, Lew. I'd forgotten about it while I
didn't have access to computers. JAC had paranoia over Year 2000. It
was useful to get the formulae for the various components.
At 60 degrees zenith distance (30 degrees elevation) you are observing
through two airmasses. Thus the light lost is twice the extinction
coefficient.
I agree that altitude isn't the only factor. Even in Britain, after
heavy rain the LMs can still be excellent despite the light pollution,
because the particulates and aerosols have been washed from the
atmosphere. Once the muck returns, the LM can lose a magnitude.
A typical mean observatory extinction coefficient is about 0.15 mag. in
V and 0.10 in R. However, on La Palma I've seen figures double this,
presumably from the Saharan dust. The LM was not as good there as I've
seen at other observatory sites. The IAPPP might have extensive figures
for the extinction coefficients at many sites, since most of its members
are amateur photometrists.
> Clear skies and many Sporadics folks,
On January 3 the skies were off the IMO scales again at 6400' with
counts in the mid-twenties in region 19 for example. The sporadics
were numerous---I saw 10 in about 4 minutes while I was setting up the
telescope and doing my initial star counts. Most were +4 to +6.
Still it did confirm the clarity of the night.
Not many Quadrantids, being located on the wrong side of the globe at
at low latitude. Seeing the Milky Way hugging the horizon (slighly above
the true horizon because of Mauna Loa) is some compensation. On
nights like that I feel like going back to visual observing.
Malcolm
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