(IAAC) Obj: M 27 - Inst: 24 cm dobsonian, f/6.6

Lewis J. Gramer lgramer at upstream.net
Thu Aug 26 11:32:54 EDT 2004


Limiting Magnitude is indeed a very observer-specific thing. I don't
believe it's COMPLETELY subjective - otherwise, the meteor data-
gathering methods of the IMO would never work! And recent success
in predicting meteor outbursts proves that they do in fact work well.
 
Anyway, that's off-topic for IAAC: but I did want to mention that LM
is primarily dependent on clean air, and on lack of light pollution -
and NOT necessarily on altitude above sea level! I observe meteors
(and deep sky) frequently from spots around the US (and one very
wonderful week in China for the 2001 Leonids). And my experience
is that skies in the Florida Keys - if one can still manage to escape
the ubiquitous European-style resort hotels that are sadly marring
the landscape more and more down there - can be just as dark as
those at altitudes of 2000m or more in the American Southwest.
 
The only observing site that I can unequivocally say has shown me
better Limiting Magnitudes than I often got on the best nights from
the Florida Keys in the past decade - would be the 2700m site on
Mauna Kea in Hawai'i! (The actual observatories up at 4100m could
assuredly give still better skies - but my flatlander, swamp-bottom
lungs sadly just could not manage too well up at that height! :->)
 
Now this isn't to say that the skies at SOME sites near sealevel
aren't completely overcome by heavier moisture condensation in
the air - coupled with light and air pollution... My observing in the
Florida Everglades in recent decades makes that sadly clear.
 
 
All of that said, of course, there is some reasonable debate as to
whether EXTENDED faint objects are better perceived at altitude,
than they are at sea level: I think there is definitely something to
this, particularly near the tropics, where the effects of airglow (the
natural emission of night-time atmosphere that has been bathed
in sunlight all day) can be very prominent indeed from dark sites.
And of course, where you have less air, there's also less airglow!
 
Clear skies all!
Lew
 
 

-----Original Message-----
From: netastrocatalog-announce-bounces at visualdeepsky.org [mailto:netastrocatalog-announce-bounces at visualdeepsky.org] On Behalf Of
Tudorica Alexandru
Sent: Thursday, August 26, 2004 7:32 AM
To: IAAC: Internet Amateur Astronomers Catalog of Visual Deep-SkyObservations
Subject: RE: (IAAC) Obj: M 27 - Inst: 24 cm dobsonian, f/6.6


That sky I had only once in my entire astronomer life and i think that it was an atmospheric anomaly, becouse from that point the
best sky I had it was only +7.0. I determined the limit magnitude then with the limit magnitude areas of IMO, in Boo an Cyg, where I
almost didn't had almost any star to count. (only three left). I am at 260 m altitude, but the highest observing place i can get in
Romania is at about 1800m. Two weeks ago at the perseids I had at best +6.94....
  And don't forget that the limit mgnitude is an subjective thing...
Clear skies, 
Alex

Natko Bajic <natkobajic at yahoo.com> wrote:

Wow, +7.45 sky! I had once about 6.75, maybe even 6.8,
from my observation place, 40km from cities! Amazing,
but more than a half magnitude deeper looks incredible
from "normal" altitudes. That should be over 2000m or?
We in Croatia do not have so high mountains...

I saw color in M 42 once, with 12cm refractor, but
with averted vision only, and just in traces...

Regards,N.

--- Tudorica Alexandru wrote:

> I did't used any sort of nebula filter, but i
> usually see different colours than others in nebulae
> and comets. I saw once on M 27 a green hue, but
> witht the 9 cm refractor, in +7.45 sky... I see
> colours in telescope very rare, only three times
> until now.
> Clear skies,
> Alex
> 
> 
> 
> 
> "Lewis J. Gramer" wrote:
> This was an interesting log, Alex. Were you using
> any sort
> of nebula filter (e.g., NarrowBand, UHC, OIII, or
> similar),
> when you noted the color of the Dumbbell as
> "yellow-red"?
> 
> Clear skies!
> Lew
> 
> 
> 
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