(IAAC) [amastro] Re: M81 with the unaided eye

The following interesting (if well-worn) thread is going on at
the 'amastro' mailing list this past couple of days:


I thought it might be of interest to BOTH deep-sky and meteor
enthusiasts, though for different reasons perhaps? Anyway, if
you wish to follow up, please be sure to check which lists you
are including in both your 'To:' and 'Cc:' lines, to be sure
that all cross-postings are on-topic for the targeted lists...

Forwarded without explicit permission of the authors.

Clear skies,
Lew Gramer

------- Forwarded Message #1
Digest : 306
Message: 4
   Date: Thu, 15 Mar 2001 00:01:20 -0600
   From: David W Knisely <K...>
Subject: Re: Re: M81 with the unaided eye

Shneor Sherman posted:
> My observing buddy Gregg and I saw M81 naked eye direct vision several  months ago, in very dark
> suburban skies.

Humm....the best I can do with dead-on direct vision is about 5.1 or
5.2.  M81 is listed at 6.9, so I guess I am out of the "direct vision
M81" running unless I use averted vision, which will get me past 7.0 if
conditions are good.  My best with averted vision was about 7.8 at the
Nebraska Star Party (3100 ft elevation), although more typically, it is
about 7.5 from there.  From my home site (1400 ft elevation), I can go
to about 7.0 (averted) overhead on occasion.  Anybody have some research
facts on common limits for direct and averted vision?
David Knisely  KA0CZC@navix.net
Prairie Astronomy Club, Inc.  http://www.4w.com/pac
Hyde Memorial Observatory:

*  Attend the 8th Annual NEBRASKA STAR PARTY  *
*   July 14-20, 2001  http://www.4w.com/nsp   *

------- Forwarded Message #1

Digest : 306
Message: 5
   Date: Wed, 14 Mar 2001 23:13:17 -0700 (MST)
   From: Brian Skiff <b...>
Subject: Re: Re: M81 with the unaided eye

>>  Anybody have some research
>>  facts on common limits for direct and averted vision?

     A lot depends on physiology, background brightness, etc. surely for
averted vision, and probably for direct vision at the threshold also.
The best I was able to do in admittedly a single session of trying to do
direct-vision limits was about V=4.5 one night at Anderson Mesa.  I found
it rather difficult to actually look at faint stars with genuine direct
vision---it seems I at least seem to use averted vision naturally in the 
dark as the normal way of looking.
     The averted-vision limit seems to be fairly well set in the "early 8s",
with such observations as Heber Curtis' at the turn of the (last) century,
Dave Nash's famous (?) double-blind test at Nebraska Star Party several
years ago, etc.  That limit is probably set as much as anything by the
sky background, not the faintness per se of the stars involved.  I can
usually pick up the V=7.8 star near 37 Comae on standard photometric nights
at Anderson Mesa.


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