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RA: 15h 17m 24.4s
Dec: −21° 00′ 36.4″
Ch: MSA:861, U2:334, SA:21
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=?, V=8.4
NGC 5897 is H VI 8 as well as H VI 19. JH noted the identification problem with the stars observed in WH's Sweep 209 on 25 April 1784 (see CGH, p. 109), and Auwers and Dreyer have notes about the field [Dreyer's are in the NGC, p. 223; IC1, p. 284 (combined NGC/IC edition of 1962); WH's Scientific Papers, Volume 1, p. 302; and MNRAS 73, 37, 1912]. (Marth apparently also published a note on VI 8 in 1864, but I have not seen that.) None of these folks positively identified VI 8, the only non-stellar object seen in the sweep, though Dreyer mentioned the possibility of N5897 and was leaning toward N5634 in 1912.
The confusion arose simply because 25 April was a poor night; WH noted "flying clouds and hazy" at the beginning of the sweep. Nevertheless he, hoping to see more of the great "stratum" of nebulae that he'd found the previous months, swept for just over half an hour until he was completely clouded out. The entire sweep consists of four stars and one cluster. Dreyer reproduces the sweep in the Scientific Papers:
13h 57m.... flying clouds and hazy 14 01} } 62 1d19' 7.8m -0.5} 10.7 89 1 45 7m 12.5 0 19 cluster... 25.2 59 1 16 star 25.4 -16 4 6.7m 31.... cloudy
The first column is the clock reading. Dreyer notes that WH reset the clock after the previous sweep, and that there is an uncertainty of 11 or 12 minutes in the readings. The second column is not explained, but is apparently a raw reading, approximately in arcminutes, of the relative north polar distance. The third column is reduced to relative north polar distance in degrees and arcminutes, and the fourth gives notes and object descriptions. So, the sweep consists of relative positions of four stars and one cluster.
WH's full description of the cluster clearly makes it a globular: "A very close, compressed cluster of stars, 8 or 9' in diameter, extremely rich, of an irregular round figure, a little extended. The stars are so small as hardly to be visible, and so accumulated in the middle as to look nebulous."
There are only three globular clusters in the right RA (14h to 16h) and Dec (+5d to -25d) ranges: NGC 5634, NGC 5897, and NGC 5904 (M 5). None of the historical sources mention NGC 5904, probably assuming it is too large and bright to have been WH's mystery object. As I've noted, Dreyer seemed to favor N5634 over N5897. However, N5634 is only half the size noted by WH, and has a bright star near to the southeast, and another even brighter star fairly close to the south-southwest. WH would have noted these in any description that he made of the object (as he, in fact, did; see the GC and NGC descriptions for N5634).
This leaves NGC 5897 as the most likely candidate. That it is indeed the correct object can be shown by reducing the relative clock times and polar distances for the stars to absolute values, using the equinox 1784.32 position of the cluster as the origin. That gives the following positions for equinoxes 1784.32 and (precessed to) J2000:
RA (1784.32) Dec RA (J2000) Dec RA (ICRS) Dec V BD 14 53.6 -21 12 15 06.0 -22 03 15 06 27.14 -22 01 54.6 6.14 -21 4030 15 03.2 -21 38 15 15.7 -22 27 15 16 23.01 -22 23 57.9 5.52 -21 4065 15 17.7 -21 09 15 30.2 -21 54 15 30 42.81 -21 52 42.8 7.80 -21 4128 15 17.9 -19 57 15 30.3 -20 42 15 30 36.25 -20 43 42.8 6.21 -20 4246
I've added the Tycho-2 positions, the V magnitudes, and the BD identifications to the table. It's easy to see that WH's positions are systematically too small in RA and too far south in Dec. But if the systematic differences are removed, the stars match the modern positions to within WH's usual errors (3-4 arcmin). It's also easy to see the effect of the clouds on WH's magnitude estimates, too.
Going through the exercise using NGC 5634 and M 5 as the origins shows that they could not have been WH's cluster -- there are no stars near them matching the relative positions and magnitudes noted in the sweep.
Dreyer could have performed this same exercise with the BD (I used SAO and the version of Tycho-2 online at CDS), but for some reason did not. Since it is an obvious check, and could easily have been done using the BD data, I wonder if anyone else has thought to do this over the years.
In any event, there is no doubt that NGC 5897 is the mystery object H VI 8.
Synonyms: H VI-008, H VI-019
On a cloudy night in April, 1784, William Herschel was sweeping with his 18.7-inch f/13 speculum telescope. In his Journal he wrote: "The moon is very bright, but in pursuit of the nebulous stratum I look in hopes of seeing some of the brighter nebulae in it." Herschel recorded VI.8 as "a very close, compressed cluster of stars 8' or 9' in diameter, extremely rich, of an irregular round figure, a little extended. The stars are so small as hardly to be visible, and so accumulated in the middle as to look nebulous." Because of the uncertainty in the recorded position, Dreyer has concluded this is the same object as VI.19, which was first recorded on March 10, 1785; it is described as a "beautiful large cluster of the most minute and most compressed stars of different sizes. 6 or 7' diameter, irregularly round, faint, red colour."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, pF, v irr R, vgbM, all resolved into stars 12..16th mag, diam 5' to 5.5'."
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.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
pF, loose globular cluster, diameter 8', not compressed in centre, certainly not a spiral nebula.
Knox Shaw, H. (1915) Note on the nebulae and star clusters shown on the Franklin-Adams plates. M.N.R.A.S., 76(2), 105-107.
Comments on papers by Harding (MNRAS, 74(8)), and Melotte (MemRAS 60(5)) describing objects foundon the Franklin-Adams plates; compares with plates taken with the Reynolds reflector (Helwan Obs Bull. 9-15):
NGC 5897 is a globular cluster [included by earlier authors as Class I(c) – known to be spirals.]
Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part II. M.N.R.A.S., 35(8), 280.
(Sulentic and Tifft 1973) notes that this is a 9.5 mag globular cluster.
RA 15 17 24.5 (2000) Dec -21 00 37 Integrated V magnitude 8.53 Central surface brightness, V magnitudes per square arcsecond 20.49 Integrated spectral type F7 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster .79 Core radius in arcmin 1.96. ["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) ]
by Jim Lucyk: Astronomy mag. 6/85 p78, Deep Sky #6 Sp84 p34, Burnhams V2 p1109.
Houston calls this globular "a big, splashy affair .. its 8.5 mag disk is more than 10' across and a 10-inch will resolve some stars. In the 1940's I viewed it from Louisiana with a 6-inch reflector at 25x and noted it as 'bright and mottled.' " He notes that this cluster is of mag 9 or 10, with a diameter of about 7'.
Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "10M; 8.5' extent; large and little-compressed with little, if any, central brightness; unresolved in 8-in. except for few 13M to 13.5M stars which dot the central region."
RA: 15h17m24s - DEC: -21o00'37" - Magnitude: 8.5 - Size: 8.7'
Tel: 16" S/C - 290x - 462x - Date: 29 April 2009 – Polokwane – Vis 5.2+-
Bright field stars stretch along this globular north-eastern side. The globular displays a soft round glow and with high power it reveal faint stars. It does not show a blazing core. Higher power shows the edge seem very granular and not quite round in shape.
Very difficult to discern this cluster, it blend in with the star field, but closer investigation brings to the fore two small groups of stars in random round shape. Does not at all shows a busy centre. A lot of the stars seem to share in pairs.
Easy seen in a very busy field of view. The core is very compressed and ease off in a haze towards the edge. The periphery is irregular with star light with fainter stars just off the edge. The north western edge of the cluster displays less starlight. A brighter 9.2 star is prominent just to the east of the cluster.
16-inch f/10 SCT (EP: 2-inch 32mm SW 127x 32' fov; 2-inch 14mm UW 290x 17' fov)
Large, soft slightly elongated east to west irregular faint glow. Careful observation (127x) revealed a handful of faint stars, with a definite overall sandpaper texture. Not very condensed, with a low surface brightness but gradually getting brighter to the middle. Faint stars run out towards the northwest in a zig-zag formation together with a pair of stars, which rounded it off in a special way. Brighter stars visible to the east just outside the field of view. On a cloudy night in April 1784 William Herschel was sweeping the night sky with his 18' speculum telescope. On this night he recorded this globular cluster in his books, as a compressed cluster of stars, extremely rich of an irregular round figure a little extended. (Mag 8.6; size 12.6'; brightest stars 13.3 mag.)
Saturday, 2010 September 04, 21:15 SAST
Paardeberg (33.56S, 18.85E)
SQM-L reading: 20.57 mag/sq.arcec, 12°C, heavy dew
15x70 hand-held binoculars.
A large (12 arcmin) but pretty faint globular, not really much brighter to the middle appearing as a broad nucleus with a narrow collar of hazy light.
Four 8th magnitude stars, arranged in a noticeable Y-shape, nudge the cluster to the east and north-east. These four stars provide a very convenient comparison to estimate the cluster's angular size.
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 cluster is very faint and that the stars in this globular are slightly resolvable.The stars in NGC 5897 is loosely concentrated that is just resolvable into 11th to 12th magnitude stars.The stars in this cluster looks like a large out of focus snowball glowing like a mist in the night sky.This globular cluster measures 9.7'x 4.9'.Chart No.263,NSOG Vol.2.
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:Globuar Cluster.
First Impression:This object looks like a globular cluster.
Chart Number:No.17(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field Of View:57'/6= 9.5'.
20mm Eyepiece:Field Of View:50'/5.5= 9.0'.
9.5'+ 9.0'= 18.5'.
Size in Arc Minutes:9.2'(Nucleus).
Globular Cluster is 9.2'* 3.0'.
Brightness Profile::The nucleus of this globular cluster grows brighter compared to the far outskirts of this cluster.
Challenge Rating:Moderately Difficult.
This globular cluster has moderately faint individual stars and that the stars in this cluster have an irregular appearance of bright stars which are resolved into hundreds to thousands of individual stars.This globular cluster is very large as far as most globulars are concerned and the stars are concentrated slightly like a large swarm of stars.
Observing site: Pinnacles overlook
[15h 17m 24s, -21° 1' 0"] 3-5 stars were seen with direct vision, 30-50 with averted. There was strong granulation as well. Still, a fairly faint cluster.
The Messier objects
The Bennett objects
The Caldwell list
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