Minimum aperture for globulars and galaxies

What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?


Hmm . . . you did specify *minimum* didn't you? When asked in that
manner my reply would be:

The smallest telescope I happen to own -- 80mm. I find satisfaction
in finding and identifying objects with small telescopes. Any visible
details that might greet me from within an object would be looked upon
as 'icing on the cake'.

It is satisfying to find Globulars and Galaxies in a smaller scope but it
seemed to me that the issue was about "viewing" them rather than finding
them...

jon

My experience from this past Spring in Colorado actually made me think
about this very issue. Why? Well most seasons have easy-to-view
objects, but Spring tends to be loaded with 'faint fuzzies.' I could
locate many of these Messier objects, but little or no detail was
visible in my 6" Newtonian. Those same objects in my friend's 12" SCT
looked amazing, especially the globulars. This 'finding' of mine,
dovetails nicely with the aperture sizes that sell in volume, but are
still portable, i.e., those in the 8-12" range.

Kirk



What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?
Thanks,
Bill Meyers

Bill Meyers wrote in message ...

Hello, all,
What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?

Well, this question is really quite hopeless as stated,
but I'll do my best. For simplicity, I'll consider just
four telescopes, all of which I've used fairly frequently,
and which form a vaguely equally-spaced sequence:

* 4-inch refractor
* 8-inch reflector or catadioptric
* 12.5-inch reflector
* 17-inch reflector

For viewing globular clusters, I'm never really satisfied
unless I've resolved some stars. I can't really say just
how many is enough; in fact, the view of a barely-resolved
globular cluster has a charm of its own, with a dozen
stars twinkling in and out of the halo as I apply averted
vision. But on the whole, the more stars, the better. Of
course, no amateur scope can resolve a globular cluster
fully, like a Hubble photo, where you can count thousands
of stars within a few arcseconds of the center.

Next, I would divide globular clusters into four classes.
The first class consists of 47 Tucanae and Omega Centauri,
which are truly glorious in a 4-inch refractor under dark
skies. The second class is what I would call the great
globulars. Just which ones make the grade is a matter of
taste, but anybody would include M5, M13, M22, NGC 6397,
NGC 6752, and probably another dozen Messier and far-
southern non-Messier globulars. These are pretty well
resolved in a 4-inch refractor under dark skies, and
they're really quite glorious in an 8-inch scope under
dark skies. The third class is the major globulars,
including most of the other Messier globulars and quite
a few NGC globulars. An 8-inch scope may show a few
stars in those, but it really takes a 12.5-inch scope
under dark skies to do justice to them. And finally,
there's all the other globular clusters in our galaxy,
a motley assortment. A few of them are barely detectable
even in a 17-inch, due mostly to heavy obscuration by
galactic dust.

On the whole, globular clusters survive light pollution
pretty well, but they do require extra aperture to get
views that are roughly equivalent to the dark-sky views.
Under typical suburban conditions, I would move everything
over one class. There, an 8-inch scope is just beginning
to resolve the great globulars, and a 12.5-inch scope is
required to do full justice to them.

The story is quite different when it comes to galaxies.
With a handful of exceptions, like M82, galaxies show
very poorly in the presence of light pollution. Yes,
you can get a decent view of M51's spiral arms in a
big scope from one of the darker suburbs, but I still
wouldn't call most galaxy views satisfactory unless
the skies are reasonably dark.

In discussing galaxies, I'll have to explictly exclude
the two Magellanic clouds and our own Milky Way. All
of those show some detail even to the unaided eye,
and quite a lot of detail through tiny instruments.

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.) Things improve quite
a lot in a 12.5-inch scope. All of the galaxies listed
above really begin to open up and show intricate detail,
which an 8-inch scope just hints at. And a bunch more
galaxies start to show tantalizing detail. But it
takes a 17-inch scope to start to unlock the wider
realm of galaxies -- and that's just the beginning.
I've never seen a view of any galaxy in any scope, no
matter how big, where I didn't wish for just a little
more aperture -- or better yet, a lot more.

- Tony Flanders

On 26 Sep 2004 12:00:04 GMT, (Jon Isaacs) wrote:

It is satisfying to find Globulars and Galaxies in a smaller scope but it
seemed to me that the issue was about "viewing" them rather than finding
them...

Anything that can be found and seen can be viewed.

If one observes carefully and notes the observed details then aperture
ceases to matter. It's just as rewarding to note all visible details
seen with an 80mm aperture as it is with any larger aperture.

To some it's the process of observing that's satisfying. To others
it's a matter of whether or not they can see the same detail(s) that
someone else has claimed to see -- regardless of aperture and sky
conditions.

One group is easily pleased. The other is encouraged and harvested by
the telescope sells industry.

Sketcher
To sketch is to see.

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/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

"Sketcher" wrote in message
...
On Thu, 23 Sep 2004 20:06:53 -0400, Bill Meyers
wrote:

What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?

Hmm . . . you did specify *minimum* didn't you? When asked in that
manner my reply would be:

The smallest telescope I happen to own -- 80mm. I find satisfaction
in finding and identifying objects with small telescopes. Any visible
details that might greet me from within an object would be looked upon
as 'icing on the cake'.

As long as a person doesn't have unrealistic expectations for what
they ought to see with a given instrument they ought to be able to
find the views satisfying. It shouldn't matter if they're using 8x42
binoculars or a major observatory telescope.


Well that is a very honest opinion but lets face it, the average star party
is loathy littered with every kind of Dob underthe sun..and that spells
aperture aperture apeture.

Most observers casual or otherwise just don't think like you. Except me.

David Knisely wrote in message ...

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.

You're absolutely right -- it's all a matter of how much detail you want.
Even a 60mm scope is big enough to classify most of the Messier galaxies
as spiral versus elliptical with a reasonably high degree of confidence,
and M31 is obviously a spiral to the naked eye. Not that you can see
the spiral arms, but no elliptical galaxy could possibly have that
shape and that kind of central condensation.

Josh Roth here at S&T told me that he recently glimpsed M33's spiral
arms using an O-III filter in his 60mm refractor, and 60mm is certainly
enough to see the emission area NGC 604 in that galaxy. I've heard of
people seeing M31's dust lanes in hand-held binoculars, although I'm
sure that feat is far beyond me.

- Tony Flanders

Total Mikal posted:

Well that is a very honest opinion but lets face it, the average star party
is loathy littered with every kind of Dob underthe sun..and that spells
aperture aperture apeture.

Is this a problem?

--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

(Tony Flanders) writes:

Even a 60mm scope is big enough to classify most of the Messier galaxies
as spiral versus elliptical with a reasonably high degree of confidence,
and M31 is obviously a spiral to the naked eye. Not that you can see
the spiral arms, but no elliptical galaxy could possibly have that
shape and that kind of central condensation.

You are exaggerating _grossly_ on both acounts, IMO. First, a small
scope (most scopes, really) typically shows just the central hub of
spiral galaxies, and these are not much differen from ellipticals.
Second, one only has to glance over at neighboring M110 to see an
elliptical galaxy that looks very similar to the naked eye view of M31.

pej
--
Per Erik Jorde

Per Erik Jorde posted:

Even a 60mm scope is big enough to classify most of the Messier galaxies
as spiral versus elliptical with a reasonably high degree of confidence,
and M31 is obviously a spiral to the naked eye. Not that you can see
the spiral arms, but no elliptical galaxy could possibly have that
shape and that kind of central condensation.


You are exaggerating _grossly_ on both acounts, IMO. First, a small
scope (most scopes, really) typically shows just the central hub of
spiral galaxies, and these are not much differen from ellipticals.
Second, one only has to glance over at neighboring M110 to see an
elliptical galaxy that looks very similar to the naked eye view of M31.

Well, he might be exagerating a little, but a good 60mm refractor when used at
a *low* enough power under reasonably dark skies will show M31 and its much
fainter extended outer haze. Its core region is usually the only thing which
shows up well at the moderate powers that many of the common "department
store" refractors use, but drop that power to 20x and the faint vaguely patchy
outer extensions become quite easy to see, along with the marked dropoff of
light intensity along the northwest side marking the location of the first
major dark lane. This kind of brightness profile (small brighter nuclear
region and extended faint outer haze) is enough to show that M31 is a spiral
galaxy, although it does not show what kind it is nor does it show much of the
arm structure. M110 on the other hand does not show the kind of smaller and
markedly brighter central core which would hint at it being a spiral. Its
smooth edges, slowly increasing brightness level with decreasing distance from
the center, and the lack of a smaller fairly well-defined brighter (but
non-stellar) core indicate that it is probably an elliptical galaxy, an
impression which is confirmed with larger apertures.
It is quite easy to use the overall brightness profile of galaxies which
show little other structure to get at least an idea of whether they are
spirals or ellipticals. In addition, with an 8 or 10 inch telescope, I can
usually tell what kind of galaxy I am looking at for a *large* number of
galaxies as faint as 13th magnitude (or sometimes fainter). With that
aperture, I can usually see at least some indications of structure (mottling
or irregular edges, small bright nucleii, dark lanes) that can point to the
object being a spiral without necessarily seeing the spiral arms. Of course,
with a ten inch, there are a number of galaxies which will visibly show the
spiral structure, so for those at least, there is little doubt of the
classification. Even without those, the brightness profile is sometimes
enough on its own to tell whether a galaxy is an elliptical or a spiral.
Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************