Globular True Diameters
The following of the Top 10 globulars of most notoriety, gives the true size of the globular from their apparent dimensions in a telescope expressed in arcmin and the known distances measured in parsecs. All basic information is taken from data in tables of Harris (2007), and I have calculated the Visual True Diameter.
Globulars are certainly much bigger than the outliers we do see the telescope, with the likelihood that stars still can be attached are roughly three or four times this diameter. Asking where the end of any globular cluster gravitationally is like asking how long is a piece of string, as the gravitational influence of the majority of the core stars extends theoretically for literally 1000's of parsecs! (actually infinitely if you wanted to be absolutely pedantic, even though it is impracticable in usefulness!)
Calculated Diameters
NGC 5139 (ω Cen) 55 arcmin 5200 pc
Visual True Diameter=83 pc
NGC 104 (Tuc) 50 arcmin 4600 pc
Visual True Diameter=67 pc
M22 / NGC 6656 (Sgr) 32 arcmin 3100 pc
Visual True Diameter=29 pc
NGC 6397 (Ara) 31' 2200 pc
Visual True Diameter= 20 pc
NGC 6752 (Pav) 29' 4200 pc
Visual True Diameter= 35 pc
M4 / NGC 6121 (Sco) 36' 2100 pc
Visual True Diameter= 22 pc
M5 / NGC 5904 (Ser) 23' 7600 pc
Visual True Diameter= 51 pc
M13 / NGC 6205 (Her) 20' 7200pc
Visual True Diameter= 42 pc
M12 / NGC 6218 (Oph) 16' 5500 pc
Visual True Diameter= 26 pc
NGC 2808 (Car) 14' 9200 pc
Visual True Diameter= 37 pc
M55 / NGC 6809 (Sgr) 19' 5200 pc
Visual True Diameter= 29 pc
NGC 6451 (CrA) 15' 6900 pc
Visual True Diameter=38 pc
The mean diameter of these globulars here is about 40 pc or 145 ly. across.
Note: Diameters for globulars can be measured in either the; Core , Half-mass or Tidal radius (expressed in arcmin). These are useful astrophysically, but express little in terms of usefulness to the novice.
Note 2: The further away the globular is the larger error in the visual size of the globular becomes. I.e. The outliers are harder to see. The smaller values given here are likely larger than stated!
Last edited by Enchilada; 02-07-2009 at 03:22 AM.
Reason: Fixed M4 calculations, 40 pc or 145 diameter (not 39pc 120ly)
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