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RA: 20h 53m 27.91s
Dec: −12° 32′ 13.4″
Ch: MSA:1336, U2:299, SA:16
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=9.95, V=9.27
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In the Philosophical Transactions, 1814, William Herschel wrote "October 30, 1810. 40 feet telescope ... Magnifying power 280. Having been about 20 minutes at the telescope to prepare the eye properly for seeing minute objects, the 72d of the Connoissance des Temps came into the field. It is a very bright object. It is a cluster of stars of a round figure, but the very faint stars on the outside of globular clusters are generally a little dispersed so as to deviate from a perfect circular form. The telescopes which have the greatest light shew this best. It is very gradually extremely condensed in the centre, but with much attention, even there, the stars may be distinguished. There are many stars in the field of view with it, but they are of several magnitudes totally different from the excessively small ones which compose the cluster. It is not possible to form an idea of the number of stars that may be in such a cluster; but I think we cannot estimate them by hundreds. The diameter of the cluster is about 1/5 of the field, which gives 1' 53.6 arcseconds." In the Philosophical Transactions, 1818, William Herschel wrote: "1805, 7 feet telescope. With a power of 80 the stars may just be preceived. 1783, 1810, 10 feet telescope, With 150 power fairly resolved. 1784, 1788, 20 feet telescope. A cluster of very small stars. 1810, large 10 feet telescope. A globular cluster; its diameter is 2' 40 seconds. 1810, October 30, 40 feet telescope. A beautiful cluster of stars."
This globular cluster, lying in the extreme western corner of Aquarius, is described in the NGC as pretty bright, pretty large, round, gradually much concentrated towards the middle, well-resolved, clearly consisting of stars.
Discovered in 1780 by Mechain, Messier confirmed it two months later. He thought it to be about 2' in diameter
Hinks, A. R. (1911) On the galactic distribution of gaseous nebulae and of star clusters. MNRAS, 71(8), 693-701.
List 6: "NGC numbers of clusters classed as globular, not in Bailey's catalogue"
Bailey, S.I. A catalogue of bright clusters and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
Burnham notes that M72 is one of the more "open" clusters, and notes that Shapely compares its degree of concentration to that of M12 and M4. Burnham says that "this is not one of the more brilliant globulars, and generally may be described as unimpressive except in large telescopes."
Hogg's 1963 catalogue of globular clusters lists it at apparent diameter 5.1' and total integrated photographic magnitude of 10.25 The brightest cluster member is roughly of 15th magnitude, so resolution of the cluster is difficult.
RA 20 53 27.9 (2000) Dec -12 32 13 Integrated V magnitude 9.27 Central surface brightness, V magnitudes per square arcsecond 18.90 Integrated spectral type F7- Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.23 Core radius in arcmin .54. ["Catalog Of Parameters For Milky Way Globular Clusters", compiled by William E. Harris, McMaster University. (Revised: May 15, 1997; from http://www.physics.mcmaster.ca/Globular.html; Harris, W.E. 1996, AJ, 112, 1487) ]
The RNGC (Sulentic and Tifft 1973) notes that this is a 10.0 mag globular cluster.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Hartung notes that "it is of the open little compressed type, irregularly round, about 1.5' across and resolved into star points which may be seen scattered in the luminous haze with 20cm, while 10.5cm shows an easy nebulous spot. Two wide pairs nearby south following and following add interest to the field."
Jack Bennett, observing with a 5" Moonwatch telescope at 21x, classified this globular as C2, which means the cluster is faint, seen only with difficulty, angularly small, almost stellar and easily missed whilst sweeping.
Indeed Walter Scott Houston likens it to a "tail-less comet." Its catalogued size is given as 6', and Houston comments that in his 4-inch Clark it is usually unresolved, but "at 200x on exceptional nights the edges begin to break up. The 10-inch [reflector] has revealed a sheen of stars across the entire disk." With a 13-inch reflector, the edges of the cluster are well resolved. Houston notes that "even experience deep-sky observer Steve Gottlieb could only resolve 20 stars in the cluster with a 17.5-inch reflector."
K G Jones speaks of it as "surprisingly difficult to resolve for so large and unconcentrated a cluster."
Phil Harrington (1990, Touring the Universe through Binoculars) calls it "the faintest of the 29 globulars listed in the Messier catalogue . . it is detectable as a slightly fuzzy point of light in 7x glasses. Giant glasses may make it a bit more obvious, but do little else to improve the visual impression of this 60,000-light-year-distant swarm."
Steve Coe, using a 17.5" f/4.5, notes: "(M 72) Bright, pretty large, round, much compressed, much brighter in the middle. Easily resolved at 150X. Has a inner bright region with a well-resolved outer section which showed 20 stars resolved on a night I rated 7/10 for seeing. Seen in 10X50 finder. 13" pretty bright, pretty large, much brighter middle, triangular shape, 12* resolved at 220X on a 5/10 night from Buckeye. 13" Sentinel 8/10 11X80 just seen. 100X pretty bright, pretty large, round, considerably compressed middle, not resolved at low power. 220X 11 stars counted, much compressed, 330X 15 stars counted, a poor Messier glob."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "8.6M; 3' diameter; fairly unremarkable but easily resolved object; 1.5 degrees to E is M-73 (you talk about excitement!)."
Observer: Lew Gramer; Your skills: Intermediate; Date and UT of Observation: 1997-07-25/26, 04:15 UT; Location: Medford, MA, USA (42N); Site classification: urban; Limiting magnitude: 5.8 (zenith), intermittent haze; Seeing: 5 (out of 10 highest) - mediocre; Moon up: yes, 50% (not visible at site); Instrument: 7x50mm Simmons binoculars
Mu Aqr forms the N tip - and eta Aqr the W "wing" - of a tiny asterism shaped very much like "Crux", the S Cross, the whole of which fits in a single binocular field (4o). M72 was 1 bino field S of and "pointed to" by the N-S axis of this Cross. The globular required averted vision AND field motion ("jiggling") to be seen against the skyglow of Boston; but it WAS visible, embedded in the E edge of an isoceles triangle of stars whose W apex is mag 6 and whose N vertex is the mag 7 star of the "Cross".
POSS: *s 2'.1 SSE (V=12.4) has V=15.2 comp, 3'.2 S (V=11.9), 2'.1 NE
(V=13.6). mags from MNRAS 157:281, which shows V(tip)=14.2.
6cm - faint w/assoc * to NE.
8cm - mod f, sm, on E side of m6 *. BS, 24Jul1982, Anderson Mesa.
- pretty f, losfcbr; no wonder it was mistaken for a comet. BS, 15Sep1982, Anderson Mesa.
15cm - superfaint---averted vis needed. 3' diam w/many f *s in fld. broad center and gran @ 101x. HM/BS, 28Jun1971, FtL.
- mod br comet-like glow @ 30x w/a couple of br fld *s nrby on E, also sev vf fld *s closeby looking like res outliers. grainy @ 80x. 165x shows ~dozen res *s on periphery plus 6-8 more over core. halo reaches m13.5 * NE 3' away (most consp * there); reaches sl beyond closer of two brtr *s S. mod even concen. 30x: there seems to be a sub*ar nuc, but not vis at higher powers. BS, 8Sep1988, Anderson Mesa.
25cm - 244x: 2'.5 diam and fairly well res. two widely spaced *s S. broad concen, round. BS.
- gran and fairly br @ 65x. 140x/190x: gran to partially res, broadly brtr across center. 2'.5-3' diam, seems irreg round, poss flattened a bit, elong E-W. consp m13 * on SE edge of halo. BS, 14Oct1982, Anderson Mesa.
30cm - 149x gives only sl res w/smooth bkgrnd. NW side has brtr *s. at 238x there is a * or *ing on NE edge of core. core 1'.25 across. outliers better res, partic on NE w/overlay of f *s on core. 2' diam at most. unevenly and broadly concen w/`shadows' on S and E. CBL, Roof.
8-inch Newtonian, 66x: 1995-06-19 "Almost invisible; very big; uniform brightness." [Gabriel Giust, San Isidro, Argentina]
Location: Campsite (South 23 16 East 29 26).
Sky conditions: Clear, steadiness good.
Instrument: Meade 8 inch, Super wide-angle, 18mm eyepiece; 36.2' fov
DSO Report N
Pretty large, bright irregular round cluster, not very dense, Resolved in stars, getting brighter to the middle. Two stars nearby to the southeast round it off beautifully. About 5 arc minutes.
12-inch f/10 SCT (76x, 95x)
Could not resolve the core, averted better. If I moved my eye around the globular I could see faint splinter stars just away from the core. Nice string to the north.
16-inch f/10 SCT (EP: 2-inch 32mm SW 127x 32' fov; 2-inch 14mm UW 290x 17' fov; 2-inch 8.8mm UW 462x 11' fov)
Pretty large irregular round puff of light that does not appear very dense. Very granular with only a few faint stars visible in the outer edges with averted vision. Brightens relatively fast to a core that appears square and not round although very hazy. To the southeast a 9.4 magnitude white star can be seen, as well as a show peace double stars to the east that rounded of this object. Discovered by Mechain in 1780.
Sky Conditions:The fainter parts of the Milky Way are barely visible.Haziness only visible on the horizon.Atmosphere stable with little interference.
This globular clusters stars are only partially resolved and that this cluster is seen as a mottled diffuse snowball.The central nucleus of this cluster is fairly condensed and that the stars in this globular cluster is slightly loosely concentrated towards each other.This globular cluster measures 3.4'x 2.6'.Chart No:31,NSOG Vol.1.
Instrument:12-inch Dobsonian Reflector Telescope.
Sky Conditions:The fainter parts of the Milky Way are barely visible on the horizon.
Transparency of the Sky:Haziness only visible on the horizon.
Seeing:Atmosphere stable with little interference.
Object Type:Globular Cluster.
First Impression:This object looks like a globular cluster.
Chart Number:No.13(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field Of View:57'/14= 4'.
20mm Eyepiece:Field Of View:50'/12.5= 4'.
4'+ 4'= 8'.
Size in Arc Minutes:4'(Nucleus).
Globular Cluster is 4'* 1.3'.
Brightness Profile:Straight from the central nucleus of this globular cluster it grows brighter compared to the central outskirts.
This globular cluster is very faint that the stars are unresolved and no individual stars are seen in this cluster.This globular cluster looks like a small round blur of faint light.It almost looks like an out of focus snowball.The stars in this cluster are uniformly concentrated towards each other.
Location: Night Sky Caravan Farm, Bonnievale.
Date: 2016 Oct 30, Sunday.
Time: 23:04 SAST
Telescope: Little Martin (4-inch f/6.5 Celestron refractor)
45-mm Celestron Plossl (15x): very very subtle feature.
11-mm Nagler Type6 (60x): Pretty small, faint globular cluster, with a broad centre.
The Messier objects
The Bennett objects
The Caldwell list
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