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Re: (meteorobs) Re: LM's and the Milky Way
Op Sat, 29 Aug 1998 GeoZay@aol.com schreef:
>
> lunsford>>George it is obvious that you must have a perception approximately
> 0.8
> magnitudes lower than Marco and I. If I see a 6.0 sky you will rate it
> 5.2. If I see a 6.8 sky you will rate it as 6.0. It is not that you are
> seeing the Milky Way under a brighter sky but rather that you rate the
> LM as being lower. The sky brightness will be the same for the both of
> us.
>
> In summation, I believe that when George and I get together we see the
> same sky brightness, the same Milky Way, but the estimated LM's will be
> 0.8 magnitudes apart due to different perception factors.<<
>
> This seems to make more sense to me than anything else I've came across about
> it. The hurdle that I had to jump over was the concept that the sky brightness
> and the Milky Way would appear the same to us. It's just that I'm unable to
> see dimmer stars not much beyond 6.0. Once I have a dark sky and reach a 6.0
> LM, I seldom see very much of a change for the rest of the night unless
> something more overwhelming occurs...namely dawn, moonrise or a cloud that
> bounces ground light into the sky from the local Indian Casino.
> George Zay
>
This also points out that for fuzzy extended phenomenon like Milky Way
the sky quality in terms of background contrast (dark- light skies) is
more important than Lm. As I already mailed to Lew and George privately:
last week I observed under really 'shitty' conditions from Biddinghuizen:
that is, with lots of haze. But that location is very, very dark: we
reached Lm 6.3-6.4 with a well visible milky way. At Voorschoten, which
is in a light polluted suburban area, I reach similar Lm on very good
nights, but the milky way is much less impressive.
The apparent upper limit to the Lm a person can estimate as pointed out
by George for his case (6.0 in his case) is interresting, since I have
noted a similar phenomenon myself, albeit (and there we go again: this is
in line with what Bob explains and I already alluded to!) in my case the
upper limit seems to be 7.0-7.1. I reach up to 6.8-6.9 and occasionally
(very rare) 7.0 from Biddinghuizen. In Southern France and Spain I
reached 7.0. But even under the best of conditions, I have never come
higher, similar to George's 'upper limit' which in his case is at 6.0. For
example, I observed
from 2100m Calar Alto observatory in the Spanish Sierra during the alfa
Monocerotids of 1995. The sky there was much darker than in Alcudia
(lower Guadix-Baza basin in southern Spain) the previous nights, with
gegenschein and even the faint 'light bridge' really blazing from the sky.
But my Lm was almost similar (6.8-7.0 from Alcudia: 7.0-7.1 from Calar Alto)!
Perhaps, due to some reason, there is a upper limit to your perception.
Most likely, where that limit lies is personal. I.e., even from the
mentioned Calar Alto I never obtained the 7.3 Lm's of for example Norman,
nothwithstanding extremely good sky conditions.
-Marco
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