Minimum aperture for globulars and galaxies

Tony Flanders wrote:

Steve O'Meara can obviously see a lot of galaxy structure
in a 4-inch refractor, but for normal mortals, I think
that 8 inches is the minimum. And even then, only a
handful of galaxies show decently -- M31, M33, M51,
M101, M83, M82, M66, maybe M81 under pristine skies.
(I'm sure I've forgotten some.)

If the 4 inch refractor is used at the proper power and under reasonably-dark
skies (ZLM 6.0 or fainter), many people (other than Steve O'Meara) can see at
least some structure or detail in a number of galaxies with averted vision.
M31 begins to show some of its spiral structure in a low-power wide-field
eyepiece, along with at least one of its dark lanes, although like most
galaxies, it isn't all that bright. M51 will show a sort of "ring" structure
hinting at its spiral nature, while M101 will also show some patchyness in its
outer haze at low to moderate power. I can see a large diffuse patch in one
end of M81, although it doesn't show the spiral arms in a 4 inch. M82 and
M104 will show some dark lane-like structure, while a number of edge-on
spirals like NGC 4565 will show their needle-like form fairly well. NGC 253
looks mottled, as does M33 (one arm starts to become visible), NGC 2903, M66
and a few others. As for an 8 inch, this aperture increases the number of
galaxies which show at least some kind of detail by quite a bit, although with
many of the fainter ones, any structure that is visible is mainly mottling,
overall shape, star-like nucleii, or, in the case of near edge-on spirals, a
dark lane. Observing galaxies is always a challenge, and learning how to
tease out some of the detail that is visible is part of the fun. Clear skies
to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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