How many globular clusters can you resolve with a small scope ?

[skysurfer]

Here I mean an 8 or 10cm refractor scope.

What I tested:

10cm (Televue Genesis): Omega Centauri, 47 Tucanae (mostly), M13, M15, M92, M3 partially.
8cm (shorttube f/6.25) : M13 (partially), M3 (hint), omega Cen and 47 Tucanae not tested as I did not bring this scope on travel.

[AG Hybrid (Adrian)]

There's some bright ones in Sagittarius. M22, I would call a show piece object. There are some other M-objects up there too that should be within reach. Theres over a dozen between Sagittarius, Ophiuchus and Scorpio that are under mag 10.

But if you really want to resolve them into individual stars. Aperture is the only road - as you would know, judging by your equipment.

[Weltevreden SA (Dana)]

It's encouraging to remember that Messier used a 75mm refractor. That was in the days before Fraunhofer doublets and even Plössl-design eyepieces. Most eyepieces were Ramsdens or Huygens, with field views not much wider than looking through a table straw. The crispness and colour accuracy we take for granted didn't exist, though the seeing conditions with v.little if any light pollution made Paris into something of a dark site with canyon horizons from nearby dark houses. When Abbe LaCaille came to the Cape of Good Hope (now Cape Town) S Africa, he cataloged over 10,000 star positions and quite a lot of bright clusters using a 20x telescope with a 12.5mm objective. That's only about three times the light-gathering power of our eyes. (And Cape weather would drive any astronomer to despair.) My first scope was a 20x 40mm 'spotting scope' used for rifle target practice, with maybe a 30° field. Even hand-held, this scope served me for many years and I still use it now and then for nostalgia reasons. It resolves some stars in 47 Tuc and 6752 in Pavo (but just a glow in O Cen), and has no trouble with M4, M80—and this hand-held using a fence post for a prop. No matter what kind of scope you have, it's what you do with it that counts. For me, useful astronomy comes from note-keeping and taking a lot of time on each object waiting for its specialness to shine through. Sort of like girlfriends and good food, but cheaper than both.

[Rob_K]

Originally Posted by AG Hybrid

But if you really want to resolve them into individual stars. Aperture is the only road - as you would know, judging by your equipment.

Yep, that pretty much sums it up! I've seen 105 MW globular clusters through my 4.5" reflector from my backyard, but only a small percentage would be resolvable in that aperture. Have to do a countback sometime. However there's probably a bit of an issue with what 'resolvable' means. I'm thinking that on a good dark night with excellent seeing (the latter rare around my neck of the woods!) you can start to perceive graininess in some of the dimmer clusters that normally appear diffuse but I don't imagine you'd class that as 'resolved'. Superior optics in a good refractor would no doubt help too.

Cheers -

[bigjoe (JOSEPH)]

Hi all.Sometimes it all depends on the globs altitude.When its lower than say 30 degree s from a horizon I dont bother in a smaller apperture.But nearer the zenith my 5" mak will resolve quite a number such as Tuc 47, omega, 6752(a fav) m55,m22 and others at higher powers Altitude above the horizon makes a huge difference in appearence from grainness to partial /good resolution.Otherwise my 10SCT is needed down low.Bty Have a look at m11 dosen't it look like a glob wow!Cheers all