Globular clusters

[A budding astronomer]

Globular clusters, whenever I point my scope towards 95% of them they come out as a hazy patch. The only two globulars I can see kind of clearly are the Hercules cluster and Messier 3 in Canes Venetici. All the rest look fuzzy, What aperture would you need to see them clearly? I have a 4.5" reflector.

Thanks

Adam

[estwing]

They certainly come alive in a 10" dob!.... 

[John]

Globulars get better the more aperture that you turn on them. Personally I think an 8" starts to show the brightest well and at 10" - 12" many have good resolution and the brigtest can look almost like their photos on a good night. I once viewed M13 through a 20" scope and the view stayed with me for a long, long time !

 

[rockystar]

I think darker skies help too. At home in my 8" M15 is a fuzzy smudge, but stars start to be resolved under darker skies. In a 22" it looks amazing!

[cotterless45]

4" frac can give you enough contrast to increase magnification and get lots of resolution,

Nick.

[Stu]

I reckon 8 to 10" would give you an excellent view of the bigger globs, with good resolution of the stars.

As Nick says, a 4" frac will show a decent view, but you need a good sky and probably averted vision to pull the stars out clearly.

[timwetherell]

Actually to my taste, there's such a thing as too much aperture for globulars. In my friends 24" Newtonian the bigger ones are too bright so they look rather "fake". My 7" refractor will definitely resolve most pretty well but probably something around 12 to 14" is the Goldilocks zone in IMHO. Though I accept that the conventional wisdom and general consensus is the bigger the better

[estwing]

28 minutes ago, timwetherell said:

Actually to my taste, there's such a thing as too much aperture for globulars. In my friends 24" Newtonian the bigger ones are too bright so they look rather "fake". My 7" refractor will definitely resolve most pretty well but probably something around 12 to 14" is the Goldilocks zone in IMHO. Though I accept that the conventional wisdom and general consensus is the bigger the better

I think you might be on your own there....too much aperture?!!!

[faulksy]

36 minutes ago, timwetherell said:

Actually to my taste, there's such a thing as too much aperture for globulars. In my friends 24" Newtonian the bigger ones are too bright so they look rather "fake". My 7" refractor will definitely resolve most pretty well but probably something around 12 to 14" is the Goldilocks zone in IMHO. Though I accept that the conventional wisdom and general consensus is the bigger the better

never ever heard that before, bigger is always better

[niallk]

I have a 10", and it gave me a wow for sure on M13  But still a bit dim...

However, stepping up to a 15" has been a revelation - especially on globs

http://www.obsessiontelescopes.com/m13/index.php

[John]

46 minutes ago, niallk said:

I have a 10", and it gave me a wow for sure on M13  But still a bit dim...

However, stepping up to a 15" has been a revelation - especially on globs

http://www.obsessiontelescopes.com/m13/index.php

There is an interesting row in the table of data on that page called " Contrast Limit: (minimum diameter before a nebular object fades from view) ". The limits start at 11 arc minutes for the 12.5 inch aperture and reduce to 3.4 arc minutes for the 25 inch. I'm having difficulty getting my head around what this actually means in practice although I'm sure its significant ?

 

[BeanerSA]

I would recommend a southern declination. We have the 2 best globs ;-)

[YKSE]

2 hours ago, John said:

There is an interesting row in the table of data on that page called " Contrast Limit: (minimum diameter before a nebular object fades from view) ". The limits start at 11 arc minutes for the 12.5 inch aperture and reduce to 3.4 arc minutes for the 25 inch. I'm having difficulty getting my head around what this actually means in practice although I'm sure its significant ?

 

It looks like these numbers are deducted from Rayleigh Resolution limits the row above. they are all roughly 16x(Rayleigh limit). Don't know where 16 comes from though. if it's related to Rayleigh limit, then my guess is that for 8", globula smaller than 11' can't be resolved because of nebulosity, while for 25", this limit is 3.4', or something in that style.

[Davesellars]

With an 8" SCT most Globular Clusters in the Messier catalogue resolved (at least something) with some exceptions.  Some are really great like M13, M92, M10 and M12.   But outside of the Messier objects they get difficult to resolve anything.  I haven't had enough time with the 12" to see how much difference the jump to this aperture is on the fainter objects - however M13 was a revelation for the brief period I caught it.

[timwetherell]

7 hours ago, BeanerSA said:

I would recommend a southern declination. We have the 2 best globs ;-)

Omega Centauri and 47 Tucanae?  The latter is my favourite globular in the whole sky, something about the condensed core and wispy outer shell. It's one of the things I miss about Australia! I don't really know why, but Omega doesn't do that much for me to be honest. It's definitely by far the biggest out there though and one to tick off every skywatchers bucket list  

I read an interesting article somewhere about some guys in Yorkshire observing Omega Centauri on a hill top when it was 2 or 3° above the horizon - Might give it a bash myself from Somerset if the clouds ever clear!

[mikeDnight]

On 05/12/2016 at 17:46, A budding astronomer said:

Globular clusters, whenever I point my scope towards 95% of them they come out as a hazy patch. The only two globulars I can see kind of clearly are the Hercules cluster and Messier 3 in Canes Venetici. All the rest look fuzzy, What aperture would you need to see them clearly? I have a 4.5" reflector.

Thanks

Adam

Adam, try getting thoroughly dark adapted by blocking out any stray light from entering your eye from the side. A sheet of black material over your head and eyepiece can greatly improve the views of fuzzy objects. Don't even look at an illuminated hand controller! Allow your eye to naturally scan the field of view. Also, using averted vision will help to bring out the finer detail. It will take you 20 minutes to attain dark adaption but the difference it makes can be astounding.

Mike

[BeanerSA]

20 hours ago, timwetherell said:

Omega Centauri and 47 Tucanae?  The latter is my favourite globular in the whole sky, something about the condensed core and wispy outer shell. It's one of the things I miss about Australia! I don't really know why, but Omega doesn't do that much for me to be honest. It's definitely by far the biggest out there though and one to tick off every skywatchers bucket list  

I read an interesting article somewhere about some guys in Yorkshire observing Omega Centauri on a hill top when it was 2 or 3° above the horizon - Might give it a bash myself from Somerset if the clouds ever clear!

Yup, that's them. I'm always stunned by Omega Centauri, because it is a naked eye object. I can see it without the aid of binoculars or telescope.

Let me know how you go with your hilltop observation attempt!!

[A budding astronomer]

I live on a hilltop in Ireland and I can see the Corona Australis and Fornax and Pisces Austrinus!

[cloudsweeper]

On 12/12/2016 at 22:20, niallk said:

I have a 10", and it gave me a wow for sure on M13  But still a bit dim...

However, stepping up to a 15" has been a revelation - especially on globs

http://www.obsessiontelescopes.com/m13/index.php

I like that graphic, and it appears to demonstrate the Principle of Diminishing Returns.

So my next 'scope might well be a 16" maximum!

Doug.

[Walshie79]

Hate to say it but it's completely impossible to see Omega Centauri (declination -47.5) from the UK, even on a mountain with a sea horizon. Was the article about the stars Theta and/or Iota Centauri (which theoretically just rise south of about 54N, though I've never seen them)? Or possibly M7 (ditto)?

 

[timwetherell]

10 hours ago, Walshie79 said:

Hate to say it but it's completely impossible to see Omega Centauri (declination -47.5) from the UK, even on a mountain with a sea horizon. Was the article about the stars Theta and/or Iota Centauri (which theoretically just rise south of about 54N, though I've never seen them)? Or possibly M7 (ditto)?

 

Just looked on Stellarium and yes, you appear to be 100% correct! Perhaps it was Theta or Iota they observed and I'd remembered it wrong (which is entirely plausible!) Or perhaps they were smoking something. Either way, yes, one would have to be down in France to stand a chance  

[James Vincent]

Globular clusters start looking good in a 10 inch telescope, however omega Centauri  or O my God Centauri we called it, looks great in binoculars when observed in Australia.

[A budding astronomer]

Here in Ireland, Iota and Theta Centauri just barely skim the horizon.