Basic object information

Name: M 22
Type of object: Globular cluster
Magnitude: 5.1
Size: 17.0'

Position (epoch of date)

Right ascension: 18h 36m 36s
Declination: -23° 54' 6"
Constellation: Sagittarius

Local information

Altitude:  12° 55' 27"
Azimuth: 139° 4' 5"

Rise: 1h 10m 40s  
Transit: 5h 41m 26s
Set: 10h 12m 13s  

Star atlas chart numbers:

Herald-Bobroff Astroatlas, Chart C-61
Millennium Star Atlas, Charts 1391-1392 (Vol III)
Sky Atlas 2000.0, Chart 22
Uranometria 2000 Chart 340, Vol 2


Revised NGC/IC Catalog Data

Wolfgang Steinicke, Feb 2001

Names and designations

M 22
NGC 6656
GCL 99
ESO 523-SC4

Type of object: Globular cluster

Catalog position for epoch J2000.0

Right ascension:	18h 36m 24.2s
Declination:		-23° 54' 12"


Object information

Magnitude: 5.1
Size: 17.0'

Object classification: VII     

Saguaro Astronomy Club v7.2 Catalog Data

Saguaro Astronomy Club, August 2000

Names and designations

M 22
NGC 6656

Type of object: Globular cluster

Catalog position for epoch J2000.0

Right ascension:	18h 36m 24.2s
Declination:		-23° 54' 12"

Constellation: Sagittarius

Object information

Magnitude: 5.1
Size: 24.0'

Object classification: VII
Description: vB,vL,R,vRi,vmC
Notes: Stars mags 11...;one of finest globs

Harris Globular Cluster Catalog Data

A catalog of parameters for globular clusters on the Milky Way
Harris W.E.
Astron. J. 112, 1487 (1996, rev. 15 May 1997)

Names and designations

Cluster identification number: NGC 6656
Other commonly used cluster name: M 22

Position information

Right ascension (J2000.0):	18h 36m 24.2s
Declination (J2000.0):		-23° 54' 12"

Galactic longitude:	9.89°
Galactic latitude:	-7.55°

Distance from the Sun: 3.2 kpc
Distance from the galactic centre: 5.0 kpc

Sun-centred position components:

X: 3.1 kpc (towards galactic centre)
Y: 0.5 kpc (in direction of galactic rotation)
Z: -0.4 kpc (towards north galactic pole)

Brightness and colour information

Foreground reddening: 0.34 magnitudes
V magnitude of the horizontal branch: 14.15
Apparent visual distance modulus: 13.55 magnitudes
Integrated V magnitude of the cluster: 5.10
Absolute visual magnitude: -8.45

Integrated colour indices:

U-B: 0.28
B-V: 0.98
V-R: 0.68
V-I: 1.42

Specific frequency of RR Lyr: 7.5
Horizontal-branch ratio: 0.91
Dickens horizontal-branch morphological type: 2  
Metallicity in log10 scale (Sun=1): -1.64
Integrated spectral type: F5  

Radial velocity information

Heliocentric radial velocity: -148.9 km/sec
Observational uncertainty in heliocentric radial velocity: 0.4 km/sec
Radial velocity relative to Solar local standard of rest: -137.2 km/sec

Physical information

Central concentration [log10(Rt/Rc)]: 1.31
Core radius: 1.42 arc minutes
Half-mass radius: 3.26 arc minutes
Log (base 10) of core relaxation time: 8.62 yr
Log (base 10) of core relaxation time at the half-mass radius: 8.86 yr
Central surface brightness in V band: 17.32 mag/sq arc sec
Log (base 10) of central luminosity density: 3.65 solar luminosities per cubic parsec