Basic object information

Name: M 4
Type of object: Globular cluster
Magnitude: 5.6
Size: 22.8'

Position (epoch of date)

Right ascension: 16h 23m 48s
Declination: -26° 32' 2"
Constellation: Scorpius

Local information

Altitude:  21° 18' 46"
Azimuth: 169° 19' 49"

Rise: 23h 6m 33s  
Transit: 3h 29m 0s
Set: 7h 47m 29s  

Star atlas chart numbers:

Herald-Bobroff Astroatlas, Chart C-63
Millennium Star Atlas, Charts 1397-1398 (Vol III)
Sky Atlas 2000.0, Chart 22
Uranometria 2000 Chart 336, Vol 2


Revised NGC/IC Catalog Data

Wolfgang Steinicke, Feb 2001

Names and designations

M 4
NGC 6121
GCL 41
ESO 517-SC1

Type of object: Globular cluster

Catalog position for epoch J2000.0

Right ascension:	16h 23m 35.5s
Declination:		-26° 31' 31"


Object information

Magnitude: 5.6
Size: 22.8'

Object classification: IX      

Saguaro Astronomy Club v7.2 Catalog Data

Saguaro Astronomy Club, August 2000

Names and designations

M 4
NGC 6121

Type of object: Globular cluster

Catalog position for epoch J2000.0

Right ascension:	16h 23m 35.5s
Declination:		-26° 31' 31"

Constellation: Scorpius

Object information

Magnitude: 5.9
Size: 26.3'

Object classification: IX
Description: Cl,8 or 10 B* in line,rrr
Notes: Look for central bar structure

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 6121
Other commonly used cluster name: M 4

Position information

Right ascension (J2000.0):	16h 23m 35.5s
Declination (J2000.0):		-26° 31' 31"

Galactic longitude:	350.97°
Galactic latitude:	15.97°

Distance from the Sun: 2.2 kpc
Distance from the galactic centre: 6.0 kpc

Sun-centred position components:

X: 2.0 kpc (towards galactic centre)
Y: -0.3 kpc (in direction of galactic rotation)
Z: 0.6 kpc (towards north galactic pole)

Brightness and colour information

Foreground reddening: 0.36 magnitudes
V magnitude of the horizontal branch: 13.45
Apparent visual distance modulus: 12.78 magnitudes
Integrated V magnitude of the cluster: 5.63
Absolute visual magnitude: -7.15

Integrated colour indices:

U-B: 0.43
B-V: 1.03
V-R: 0.69
V-I: 1.42

Specific frequency of RR Lyr: 70.4
Horizontal-branch ratio: -0.06
Dickens horizontal-branch morphological type: 4  
Metallicity in log10 scale (Sun=1): -1.20
Integrated spectral type: F8  

Radial velocity information

Heliocentric radial velocity: 70.2 km/sec
Observational uncertainty in heliocentric radial velocity: 0.3 km/sec
Radial velocity relative to Solar local standard of rest: 79.8 km/sec

Physical information

Central concentration [log10(Rt/Rc)]: 1.59
Core radius: 0.83 arc minutes
Half-mass radius: 3.65 arc minutes
Log (base 10) of core relaxation time: 7.57 yr
Log (base 10) of core relaxation time at the half-mass radius: 8.64 yr
Central surface brightness in V band: 17.88 mag/sq arc sec
Log (base 10) of central luminosity density: 3.83 solar luminosities per cubic parsec