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Re: (IAAC) Obj: M33 + Help me with M81!



> Natko Bajic wrote:
> >I've also heard on IAAC that several people have seen M81 with naked eye.
> >I would appreciate any information about doing it because I'm planning a
> >trip to a 6500ft mountain this winter, where I expect limiting magnitude
> >of 7, or maybe even more. Thanks!
Brian Skiff discussed this on amastro:
As mentioned briefly in the binocular-observing post, I was able to see
M81 naked-eye last night from Lowell's Anderson Mesa dark-sky site.  In case
others would like to try this, here are some details.  For reference, have a
look at Uranometria chart 23, or the relevant chart from the new edition of
Sky Atlas 2000.
     The two galaxies lie in a string of faint stars that starts with 24 UMa
(also the variable DK UMa) at the west end, and arcs eastward and a bit
south
past M81 and NGC 3077 to a mag. 6 star appearing on chart 24 (brightest of a
triangle).  M81 in fact is one element of the string.  To have a hope seeing
M81, and to be sure to avoid confusion with a star, you need first to
identify
several of these stars.  The brighter star about 1.5 degrees west of M81 is
HD 83489, at V mag. 5.7.  Next identify the fainter star at the east end of
the string (the one on U2000 chart 24), which is HD 89343 = EN UMa, a very
small-amplitude delta-Scuti star, at V mag. 6.0.
     Now, between HD 83489 and 89343 I consistently saw (glimpsed is a
better
term, however) at least three star-like objects.  First, about 1.5 degrees
east
of M81 (and just west of HD 89343), is HD 87703, which is V mag. 7.1.  If
this
star isn't pretty readily visible (at say the 20-30 percent detection
level),
then you probably won't be able get the galaxy.  Much more difficult (at the
5-10 percent detection threshold) is the group of stars shown on the U2000
chart near NGC 3077.  These are HD 86458 (V=8.0), HD 86574 (V=8.2), and
HD 86677 (V=7.9).  I saw these three (or perhaps just the closer pair
86458/86677) as a single object.  The combined brightness of the three stars
is V=6.8, but the extended nature of the trio means the surface brightness
will be lower to the naked eye than a single star of that magnitude, making
it
more difficult to spot.
     The third object, repeatedly spotted in the same (correct) place, is
M81!
Again, this is a threshold object, which I detected only 5-10 percent of the
time with optimally-averted vision together with the other faint stars just
mentioned.  On occasion I also seemed to pick up another star, HD 85828
(V=7.7), which is about 40' south of the galaxy.
     Both NGC 253 and NGC 5128 (Cen A) are somewhat closer than M81, which
is
probably the most distant discrete object visible to the unaided eye, at
something like 3.6 megaparsecs (11.8 million light-years).
     Having tried this observation seriously (and unsuccessfuly) twice
before,
I found the key this time was getting all the field stars sorted out.
Because
there are several stars of similar brightness nearby, you really must be
able
to identify each of these in order to securely locate the galaxy.
     Brent Archinal knows of several other observers who have securely
identified M81, including himself, Steve O'Meara, Aristides Tzarellas, and
others (?).
\Brian
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