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Al di la della Luna; Beyond the Moon; Astrophotography; Astrofotografia; Danilo Pivato

 

 
 
 
 
 
 
 
The Analysis of Frame
 
M2 - Globular Cluster: in Acquarius - NGC 7089; HD 205146; h 2125; GC 4678; GCRV 13546; C 2130-010; GCl 121; BD-01 4175; [field: 0,34° x 0,68°] - - Mag. Limite: 20.5^ - 21.0^ (r) - Fonte: SDSS DR13 - Object Coordinates: RAJ2000.0 21h 33m 27.02s - Dec J2000.0 -00° 49' 23.7" [SIMBAD] - Magnitudine: 6.25^ (v); --.-^ (b), --6.84^ (r); ; Surface Brightness: --.-^ - Object Size: 13' x 13' - Position Angle: 23° - Object Classification: 2; Redshift z(~) V (Km/s): -6,7 [2.1] - Spectrum: --- Ammasso globulare scoperto da Giovanni Domenico Maraldi nel 1746 mentre stava osservando la cometa di De Chèseaux, presenta un nucleo estremamente luminoso e compatto. Apparentemente esso presenta una diminuzione di luminosità particolarmente marcata dal centro alla periferia, con una vistosa asimmetria. Le stelle più brillanti di M2 sono giganti rosse e gialle di magnitudine 13,1, mentre le sue stelle di braccio orizzontale hanno una luminosità apparente di 16,1. Il tipo spettrale nel suo complesso è F0, il suo indice di colore -0,06; fonti più recenti accreditano un tipo spettrale F4 e B-V pari a 0,66. Le stelle variabili scoperte all'interno di M2 ammontano a 42 (Christine Clement 2012 - "Christine Clement, 2012. Variable stars in NGC 7089 / C2130-010 / Messier 2. Updated March 2012. 42 variables: 23 RR Lyrae type RR0, 15 type RR1, 3 Cepheid variables of type W Virginis, 1 RV Tauri star. No pulsar found.). Le prime due sono state scoperte da Bailey nel 1895, mentre altre otto furono individuate prima del 1897. La maggior parte di esse appartiene alle cosiddette "variabili degli ammassi" o stelle di tipo "RR Lyrae", tutte caratterizzate da un periodo minore di 24 ore. Tre delle quarantadue sono Cefeidi classiche di tipo II (stelle W Virginis) di tredicesima magnitudine, con un periodo rispettivamente di 15,57, 17,55 e 19,30 giorni. Queste stelle sono state studiate da H. C. Arp (1955) e G. Wallerstein (1970). Una delle variabili più brillanti è una stella RV Tauri, scoperta nel 1897 dall'astrofilo francese A. Chèvremont, si trova a nord del bordo orientale dell'ammasso; la sua magnitudine varia da un minimo di 14,0^ a un massimo di 12,5^ in un periodo di 69,09 giorni. Nella fotografia ottenuta con il Takahashi BRC250 avente 1268mm di focale e potere risoltivo con scala 1,11"/pixel unito al ccd SBIG ST-10XME, l'ammasso globulare appare in tutto il suo splendore riempiendo per più di 1/3 il campo apparente dell'inquadratura. Incastonato tra le due stelle luminose di magnitudine 9,9^ (r), appare quasi del tutto risolto, ad eccenzion fatta per la parte centrale che continua ad essere molto addensata. Dal fondo dei dintorni di M2 emergono decine e decine di deboli galassie che, per quelle più luminose, è già possibile intravedere piccoli dettagli e forme avvincenti iniziando a percepirne il volume stesso delle galassie. Data la buona profondità della foto è stato possibile individuare e quindi localizzare sulla mappa, anche alcuni Quasar (...Continua)
 
 
 
Variable Stars in Globular cluster M2 (NGC 7089) show in the map - (by Kraemer+, 2014 )
 
ID Seq in Map RA deg Dec deg Units Period Mag Amp1 Type Note/Remarks
                   
01
V1
21h 33m 28.46s
-00° 47' 55.4"
R0
15.5647
13.36
1.1
CW
Note
02
V2
21h 33m 23.70s
-00° 48' 04.5"
R0
0.5278
16.031
1.210
RR0
Note
03
V3
21h 33m 41.62s
-00° 49' 53.1"
R0
0.6197
15.963
1.062
RR0
04
V4
21h 33m 24.72s
-00° 48' 45.0"
R0
0.5642
15.929
1.025
RR0
05
V5
21h 33m 23.84s
-00° 49' 12.9"
R0
17.557
13.28
0.85
CW
Note
06
V6
21h 33m 27.52s
-00° 49' 59.6"
R0
19.299
13.14
1.0
CW
Note
07
V7
21h 33m 36.97s
-00° 52' 22.6"
R0
0.5949
15.962
1.042
RR0
08
V8
21h 33m 22.30s
-00° 50' 11.5"
R0
0.6437
15.946
0.981
RR0
09
V9
21h 33m 15.24s
-00° 51' 23.7"
R0
0.6093
16.001
1.038
RR0
10
V10
21h 33m 32.73s
-00° 48' 35.0"
R0
0.8757
15.733
0.634
RR0
11
V11
21h 33m 32.41s
-00° 49' 05.8"
R0
67.0
12.11
1.1
RV
Note
12
V12
21h 33m 22.64s
-00° 48' 32.9"
R0
0.6656
15.909
1.007
RR0
13
V13
21h 33m 21.54s
-00° 48' 03.1"
R0
0.7066
15.921
0.839
RR0
14
V14
21h 33m 32.36s
-00° 50' 20.9"
R0
0.6938
15.969
0.759
RR0
15
V15
21h 33m 32.21s
-00° 50' 29.5"
R0
0.3008
16.077
0.456
RR1
16
V16
21h 33m 24.81s
-00° 49' 42.1"
R0
0.6559
16.013
1.012
RR0
Note
17
V17
21h 33m 26.99s
-00° 50' 17.6"
R0
0.6364
15.863
1.202
RR0
18
V18
21h 33m 14.03s
-00° 01' 05.3"
R0
0.3621
15.951
0.624
RR1
19
V19
21h 33m 42.81s
-00° 57' 43.7"
R0
0.3194
16.048
0.558
RR1
20
V20
21h 33m 53.09s
-00° 47' 56.8"
R0
0.2863
16.065
0.376
RR1
21
V21
21h 33m 48.95s
-00° 45' 45.4"
R0
0.7122
15.970
0.831
RR0
22
V22
21h 33m 26.90s
-00° 48' 32.7"
R0
0.7020
15.749
1.004
RR0
23
V23
21h 33m 32.48s
-00° 50' 03.4"
R0
0.7812
15.908
0.537
RR0
24
V24
21h 33m 27.73s
-00° 51' 04.9"
R0
0.3582
15.992
0.457
RR1
25
V25
21h 33m 26.87s
-00° 49' 55.9"
R0
0.7287
16.075
0.877
RR0
26
V26
21h 33m 31.56s
-00° 49' 22.6"
R0
0.4124
15.922
0.482
RR1
Note
27
V27
21h 33m 23.23s
-00° 47' 14.1"
R0
0.3142
15.947
0.121
RR1
28
V28
21h 33m 27.36s
-00° 47' 36.1"
R0
0.8238
15.942
0.183
RR0
29
V29
21h 33m 22.46s
-00° 50' 51.7"
R0
0.3058
16.020
0.182
RR1
30
V30
21h 33m 32.91s
-00° 48' 31.3"
R0
0.2729
16.118
0.223
RR1
31
V31
21h 33m 32.91s
-00° 49' 18.5"
R0
0.7887
16.066
0.553
RR0
32
V32
21h 33m 30.08s
-00° 49' 57.7"
R0
0.3670
16.038
0.612
RR1
Note
33
V33
21h 33m 23.42s
-00° 49' 34.5"
R0
0.3080
15.931
0.515
RR1
34
V34
21h 33m 31.30s
-00° 49' 56.5"
R0
0.3914
15.975
0.523
RR1
35
V35
21h 33m 28.00s
-00° 47' 31"
R0
0.3256
---
---
RR1
36
V36
21h 33m 30.70s
-00° 49' 12"
R0
0.2708
---
---
RR1
37
V37
21h 33m 26.00s
-00° 49' 18"
R0
0.5667
---
---
RR0
38
V38
21h 33m 31.10s
-00° 49' 23"
R0
0.8073
---
---
RR0
39
V39
21h 33m 27.30s
-00° 50' 06"
R0
0.6078
---
---
RR0
40
V40
21h 33m 25.60s
-00° 49' 15"
R0
0.7517
---
---
RR0
41
V41
21h 33m 28.00s
-00° 49' 24"
R0
0.6053
---
---
RR0
42
V42
21h 33m 28.30s
-00° 49' 51"
R0
0.3280
---
---
RR1

Supplementary Notes and References:

For V1-34: The RA and dec are from Samus et al. (2009) Periods, magnitudes, amplitudes and variability types are from Lee & Carney (1999) unless indicated otherwise in the notes on individual stars.

For V35-V42: All the data are from Lazaro et al. (2006). No magnitudes were derived because they used the image subtraction technique.

Notes on individual stars:

V1, V5, V6, V11: Periods, magnitudes, amplitudes and variability types are from Demers (1969) who published an ID chart. For V11, he listed the half period (33.5 days), but noted that the star is probably an RV Tauri variable.

V16: Lazaro et al. (2006) did not detect any star at the previously reported position for V16 and did not detect variablity in nearby stars. However, Lee & Carney (1999) derived a V amplitude of more than 1 mag for the star and confirmed the period that Sawyer (1935) derived in her discovery paper.

V2, V26, V32: Periods are from Lazaro et al. (2006) and magnitudes, amplitudes and variability types are from Lee & Carney (1999)

 
 
 
Dust Lane in M2: Una particolarità che è contenuta nell'ammasso globulare M2 riguarda una supposta banda oscura di polveri dust lane che si trova nel quadrante di NE, dando un aspetto squadrato alla parte centrale dell'ammasso. Ne ho trovato tracce bibliografiche della probabile dust lane nei recenti testi: Annals of the Deep Sky Vol. 1 di J Kanipe & D. Webb ed anche nel libro di A. Cooke: Dark Nebulae, Dark Lanes & Dust Belts, La testimonianza sull'esistenza di bande di polveri scure presenti negli ammassi globulari quali: NGC 6171, M13, M3 e M10 sembra risalire ad oltre un secolo fa. In realtà l'esistenza o meno di tali polveri scure negli ammassi globulari, non è stata ancora definitivamente risolta, Per decenni si è ipotizzato, sulla base dei migliori modelli stellari che le stelle giganti rosse, durante il loro stato evolutivo, fino a diventare nane bianche, siano state la probabile fonte delle polveri residue presenti negli ammassi globulari sopra nominati. Nel caso di M2, stando alle ultimissime ricerche sembra ancora non ci sia però la reale conferma della presenza al suo interno di polveri oscure. Pertanto la tendenza generale dei ricercatori è quella di ritenere "improbabile" l'effettiva esistenza. Il fatto poi che l'ammasso risulti alquanto asimmetrico non implica necessariamente che le polveri siano la causa dell'asimmetria. (...Continua)
 
 
Description of the other deep-sky object in the field
 

Baxendell's Unphotographable Nebula; NGC 7088; Ced 193: Object Coordinates: RAJ2000.0 RA: 21h 33m 22.0s - Dec: -00° 23' 00" [SIMBAD] - Una curiosità legata a questa zona del cielo, probabilmente poco conosciuta, riguarda la misteriosa individuazione sul finire del XIX secolo di una nebulosa diffusa situata pochi primi a nord di M2 che John Dreyer stesso classificò nel suo famoso catalogo NGC. Si tratta di una nebulosa mai fotografata e né, con molta probabilità, mai osservata realmente. La storia di questa nebulosa è legata all'astrofilo inglese Joseph Baxendell il quale ne annunciò la scoperta sul prestigioso periodico inglese: "Monthly Notices of the Royal Astronomical Society" nel 1880, segnalando una grande e debole nebulosa situata vicino l'ammasso globulare M2 ("A New Nebula," MNRAS 41, 48). La scoperta avvenne il 28 settembre del 1880 e lo stesso John Louis Emil Dreyer la inserì nel monumentale catalogo con la sigla di NGC 7088, avendola osservata egli stesso presso il suo osservatorio privato in Birkdale - quartiere di Southport (UK) - usando un rifrattore da 6 pollici. La descrizione che egli fece fu la seguente: "... irregular oval form, its longer axis lying in a nearly east and west direction" [eF, eL, dif, Epf, n of M2 *]. A queste prime e sommarie note Dreyer aggiunse che la nebulosa si trovava 25' a nord dell'ammasso globulare M2 e che presentava una dimensione di 75'x52'. In seguito scrisse ancora che la nebulosa sembrava assomigliare alla grande nebulosa vicino alle Pleiadi (scoperta nel 1859 da Tempell), ma che risultava leggermente meno brillante. La nebulosa NGC 7088 stranamente fu osservata da un certo numero di altri abili osservatori, tra cui appunto John Dreyer (1885, 6" e 10" rifrattore); Guillaume Bigourdan (1897, 12" rifrattore); Johann Georg Hagen (1915 e nel 1917, 16" rifrattore); Maximilian Franz Joseph Cornelius Wolf (1927, 6" rifrattore); Edward Dominic O'Connor (1929, 15" rifrattore); Ludwig Wilhelm Emil Ernst Becker (1930, 12" rifrattore) e Georg Lehner (1930, 4" rifrattore). Tuttavia l'oggetto non fu mai rilevato fotograficamente, nonostante fossero gli anni pioneristici della fotografia astronomica; proprio per questo motivo nel frattempo gli venne attribuìto il soprannome di: "Baxendell's Unphotographable Nebula". Negli anni a seguire con il perfezionarsi della tecnica e delle emulsioni chimiche fotografiche furono condotti ancora altri tentativi da Wilhelm Heinrich Walter Baade, Harlow Shapley, Wolfgang Paul Strohmeier e da Adalbert Max Ferdinand Adolf Gürtler utilizzando sia diverse emulsioni fotografiche e sia diversi filtri, ma sempre senza successo. Alla fine si giunse a concludere che l'oggetto nebulare non era reale e che tutte le precedenti osservazioni visuali di NGC 7088 fossero la causa di alcuni effetti fisiologici da parte degli osservatori e anche ottici da parte degli strumenti impiegati, quali probabili riflessi che avvenivano nei telescopi dell'epoca causati dall'ammasso globulare M2, assai luminoso, situato nelle immediate vicinanze. Ciò nonostante nel 1946 quando venne stilato il catalogo omonimo composto da 215 nebulose diffuse sia ad emissione che a riflessione, l'astronomo Stephan Cederblad inserì con la sigla Ced 193 la Baxendell's Unphotographable Nebula! Nel libro di Mark Bratton: "The Complete Guide to the Herschel Object" non viene fatto alcun cenno né della storia e né ad alcuna segnalazione della nebulosa NGC 7088.

Confini della nebulosa NGC 7088 secondo i vari storici osservatori - vedere la mappa - (Strohmeier, Gürtler: Veröff. Sternw. München, Bd. 4, Nr. 8, 1951) - Per esigenze di FOV, fare riferimento alle mappe delle riprese effettuate al globulare M2 con il teleobiettivo da 300mm di focale (visibile qui) e l'altra mappa scattata con il Pentax SDUF II (visibile qui)

Baxendell (1880): -----------------------------------------
Dreyer (1885) : ---------------------------------------------
Hagen (1915 - 1917): ----------------------------------------------
Wolf (1927): -------------------------------------------------
Strohmeier & Guttler (1951): ------------------------------------------
Haidrichs Schnitt (1936): --------------------------------
 
 
 
IC 1391; LEDA 67002; MCG+00-55-007; 6dFGS gJ213500.4-003041; 2MASX J21350042-0030407; SDSS J213500.39-003041.1; - Galaxy - - Object Coordinates: RAJ2000.0 RA: 21h 32m 24.785s - Dec: -01° 51' 45.08" [SIMBAD] - Magnitudine: 14.7^ (v); 15.7^ (b), 14.6^ (r); ; Surface Brightness: 11.3^ - Object Size: 0.2' x 0.2' [SEDS] - Position Angle: 162° - Object Classification: ---; Redshift z(~) V (Km/s): 0.030328 - Spectrum: --- Galassia ellittica distante da noi 414 milioni di anni luce. Scoperta da Stephane Javelle il 03 agosto del 1892 alla scala di 1,85"/pixel si nota soltanto il suo aspetto diffuso con la parte centrale del nucleo piuttosto brillante e di aspetto puntiforme e una debole stella di magnitudine 17.8^r situata in direzione WSW, distante dal nucleo 29.5". In questa piccola galassia il 24 maggio del 2010 è stata scoperta da Drake et al. (CRTS) una supernova di tipo Ia a 8.7" est e 6.5" sud dal nucleo della galassia. La magnitudine massima raggiunta è stata di 16.4^ . Le notizie relative a questa scoperta sono rintracciabili sulla circolare CBET002296
 
LEDA 1128074; SDSS J213512.09-010258.6; - Brightest galaxy in a Cluster (BCG) - Object Coordinates: RAJ2000.0 RA: 21h 35m 12.093s - Dec: -01° 02' 58.61" [SIMBAD] - Magnitudine: --.-^ (v); --.-^ (b), 17.9^ (r); ; Surface Brightness: --.-^ - Object Size: ~ 10,5" x 7,8" [ALADIN] - Position Angle: ---° - Object Classification: ---; Redshift z(~) V (Km/s): -.----- - Spectrum: --- Questa galassia che poi, come vedremo non è una galassia, si trova 1' ESE di una stella GSC 05208-00975 di 10,4^ magnitudine, situata nel quadrante basso-sinistra della foto sopra riprodotta. Si riporta questa galassia tra le note d'interesse in quanto si trova in un'area del cielo particolarmente interessante. Intanto come accennato, la LEDA 1128074 non è una singola galassia, bensì è un'agglomerato di 5 galassie vicinissime disposte in fila e tutte comprese tra le magnitudini 17,8^-18,5^ (r). Alla scala dell'immagine in questione appaiono fuse l'una con le alre e danno l'impressione di essere una singola galassia. Per rendersene conto della loro reale natura è sufficiente analizzare la lastra corrispettiva dell'SDSS. Molto vicino a questo gruppo di galassie si trova: Eyelash apostrofato in SIMBAD come. "Gravitationally Lensed Image of a Galaxy". E non è l'unico. Infatti a 1,2' più a Nord c'è un'altra Lente gravitazionale denominata: Cosmic Eye. Da considerare che sono tutti oggetti che brillano oltre la 19.0^ magnitudine!
 
 
History of Observation and description:
 
Discovered by Maraldi on September 11, 1746.
Independently rediscovered by Messier on September 11, 1760
 

Charles Messier: - September 11, 1760. 2. 21h 21m 08s (320d 17' 00") -1d 47' 00" Nebula without star in the head of Aquarius, its center is brilliant, & the light surrounding it is round; it resembles the beautiful nebula which is situated between the head & the bow of Sagittarius [M22], it is seen very well with a telescope of 2 feet [FL], placed below the parallel [same Dec] of Alpha Aquarii. M. Messier has reported this nebula on the chart of the path of the comet observed in 1759. Mem. Acad. of the year 1760, page 464. M. Maraldi has seen this nebula in 1746 while observing the comet which appeared that year. (Diam. 4')

 

Giovanni Domenico Maraldi: (September 11, 1746) "On September 11 I have observed another one [nebulous star, besides M15] for which the right ascension is 320d 7' 19" [21h 20m 29s], & the declination 1d 55' 38" south, very near to the parallel where the Comet should be. This one is round, well terminated and brighter in the center, about 4' or 5' in extent and not a single star around it to a pretty large distance; none can be seen in the whole field of the telescope. This appears very singular to me, for most of the stars one calls nebulous are surrounded by many stars, making one think that the whiteness found there is an effect of the light of a mass of stars too small to be seen in the largest telescopes. I took, at first, this nebula for the comet."

 

Johan Elert Bode: Bode 5 - Like a comet without tail. "On September 22 [1775], I discovered northward above the star Beta at the western shoulder and at the head of Aqr a new nebulous star. It appears through the 7-foot telescope in round shape, and exhibits a vivid nucleus involved in a nebula. Its actual position is west near the 24th star of Aqr, between which and the nebula another brighter star occurs, as the 13th figure shows. The 14th [figure] shows the relative position os this nebula to the closest smaller stars as seen with a 14-foot (FL) telescope."

 

Johann Gottfried Koehler: Koehler No. 14 "[Nebula] In the neck of Aquarius."

 

Caroline Lucretia Herschel: July 30. 1783. Observed M2, M16, M25 and M55.

 

Frederick William Herschel: 1800. PT 1800 (vol. 90) p. 71-72. Reprinted in: Scientific Papers, Vol. II, p. 44]

July 30, 1783. I viewed the nebula south preceding Flamsteed's 24 Aquarii, discovered by Mr. Maraldi in 1746 [M2, NGC 7089].
In the small sweeper (*), this nebula appears like a telescopic comet.
Oct. 27, 1794. The same nebula with a 7-feet reflector.
I can see that it is a cluster of stars, many of them visible.
If we compare the penetrating power of the two instruments, we find that we have in the first sqrt(41*(42^ 2-12^ 2))/2 = 12.84; and in the latter sqrt(41*(63^ 2-12^2))/2 = 20.25. However, the magnifying power was partly concerned in this instance; for in the sweeper it was not sufficient to separate the stars properly.

The small sweeper is a Newtonian reflector, of 2 feet focal length; and, with an aperture of 4.2 inches, has only a magnifying power of 24. and a field of view 2d 12'. Its distinctness is so perfect, that it will shew letters at a moderate distance, with a magnifying power of 2000; and its movements are so convenient, that the eye remains at rest while the instrument makes a sweep from the horizon to the zenith. A large one of the same construction has an aperture of 9.2 inches, with a focal length of 5 feet 3 inches. It is also charged low enough for the eye to take in the whole optic pencil; and its penetrating power, with a double eye glass, is sqrt(41*(92^2-21^ 2))/2 = 28.57.

[1814. PT 1814 (vol. 104) p. 274. Reprinted in: Scientific Papers, Vol. II, p. 535]
Sept. 4, 1799. 40 feet telescope, power 240. "I examined the 2d of the Connoiss. It appeared very brilliant and luminous."
"The scattered stars were brought to a good, well determined focus, from which it appears that the central condensed light is owing to a multitude of stars that appeared at various distances behind and near each other. I could actually see and distinguish the stars even in the central mass. The Rev. Mr. Vince, Plumian Professor of Astronomy at Cambridge, saw it in the same telescope as described."

[1818. PT 1818 (vol. 108), 429-470, here p. 345. Reprinted in: Scientific Papers, Vol. II, p. 595]
Observations of the 2nd of the connoissance des temps.
"1799, 7 feet finder telescope. It is visible as a star. 1810, it may just be perceived to have rather a larger diameter than a star."
"1783, 2 feet sweeper. It is like a telescopic comet."
"1794, 7 feet telescope. With 287 I can see that it is a cluster of stars, many of them being visible."
"1810, 10 feet telescope. A beautiful bright object."
"1784, 1785, 1802, 20 feet telescope. A cluster of very compressed exceedingly small [faint] stars."
"1805, 1810, large 10 feet telescope. Its diameter with 108 is 4' 59"; with 171 and 220, it is 6' 0"."
"1799, 40 feet telescope. A globular cluster of stars." (*)
[(*) For the particulars of this observation see Phil Trans. for 1814, p. 274 (repr. SP2, p. 535)]
By the observation of the 7-feet telescope, which has a power of seeing stars that exceeds the power ot the eye to see them 20.25 times, the profundity of this cluster is of the 243rd order.

 

John Frederick William Herschel: (1833) h 2125 = M2 Sweep 81 (July 21, 1827). RA 21h 24m 39.6s, NPD 91d 34' 11" (1830.0) [Right Ascension and North Polar Distance]
A fine large globular cluster; it shines out between the clouds, and I see the stars of which it consists; and the determination of its place is good, though there is not a star now to be seen with the naked eye for clouds. (See fig. 88)

Sweep 288 (September 12, 1830). RA 21h 24m 40.0s, NPD 91d 34' 18" (1830.0)
A most superb cluster; round; stars eS [extremely small/faint]; 12, 13, 14m; they are evidently globularly arranged, and not internally condensed towards the centre more than the spherical form would make them appear to be; but in the middle they blend into a blaze of light. It is like a heap of fine sand! With 9 inches aperture I can just see the stars; with 6 it is resolvable [barely, i.e. mottled]

Sweep 96 (October 16..18, 1827). RA 21h 24m 40.0s, NPD 91d 35' +/- (1830.0)
A most glorious cluster of stars 15m compressed up to a blaze. Its most crowded part takes 6s [in RA] to pass the wire, but there are straggling stars, although few, of the same size as the rest. There must be thousands of them. The total light of the cl[uster] not exceeding a star 6m, it follows that several thousand stars 15m = 1 of 6m.

 

William Henry Smyth: DCCLXXXVII [787]. M2. DCCLXXXVII. 2 M. Aquarii.
AR 21h 25m 10s, Dec S 1d 32'.1
Mean Epoch of Observation: 1836.72 [Sep 1836]
[with drawing]
A fine globular cluster preceding the water-bearer's neck, and about 5 deg north-half-east from Beta, the above-described object. This appears to have been discovered by Maraldi in 1746, while hunting up M. Cheseaux's comet. Some years afterwards, Messier described it as a nebula containing no star, centre brilliant and surrounded by a circular light, altogether resembling the nucleus of a comet. Maraldi shows that little was then understood about nebulae, for after mentioning that he could make out no stars, he continues, "Ce qui me parut fort singulier; car la plupart des étoiles qu'on apelle nébuleuses sont environnée d'un grand nombre d'étoiles; ce qui a fait juger que la blancheur que l'on y découvre, est l'effet de la lumière d'un amas d'étoiles tros petite pour être aperçues par les plus grandes lunettes." [translation above] Now it is well established that, even where a globular cluster may not appear insulated, the stars belonging to it may be easily distinguished from those which happen to be scattered about, or upon, it.
This magnificient ball of stars condenses to the centre, and presents so fine a spherical form, that imagination cannot but picture the inconceivable brilliance of their visible heavens, to its animated myriads. It was observed and figured by Sir John Herschel, No. 2125, who observes, that the total light of the cluster does not exceed that of a star of the 6th magnitude, it follows that several thousands of the 15th magnitude must be required to equal one of the 6th. It was tesed by Sir William Herschel with his 7, 10, and 20-foot reflectors; and he pronounced it to be a cluster of very compressed exceedingly small [faint] stars. This result was splendidly proven when, in September, 1799, he showed it to Professor Vince in that wonderful effort of the day, the 40-foot telescope: "the scattered stars," he observes, "were brought to a good well-determined focus, from which it appears that the central condensed lightis owing to a magnitude of stars that appeared at various distances behind and near each other. I could actually see and distinguish the stars, even in the central mass." By submitting it to the same process which he had already applied to fathom the Milky Way, he estimated its profundity to be of the 243rd order.
In his remarks on 2 Messier, Sir John Herschel says, "It is like a heap of fine sand!" The expression is remarkable, inasmuch as Signor Cacciatore, showing me this object in Palermo, in 1814, observed that the components were about as difficult to enumerate as "l'arena delle spiaggie marittime." This, however, is a noted method of estimating the stellar host, having been resorted to in essays, sermons, lectures, and guides to knowledge. Thus Booker, a censor of the press in 1655, compliments Bagwell for making astronomical mysteries plain to the "meanest capacity," by arithmetic:

I wax hoarse
Already, as I view thy counting course,
And thy ingenious faney, to pourtray
From sands to stars a plain and pleasant way.
 
 

William Parsons, 3rd Earl of Rosse - Lord Rosse: - [Phil. Trans. 1844, p. 321-324, drawing on plate XVIII, Fig. 88; on his observation with his 3-feet (36-inch) aperture telescope] Plate XVIII, fig. 88 is one of the many well-known clusters; I have selected it merely for the purpose of showing that in such objects we find no new feature, nothing which had not been seen with instruments of inferior power; the stars, of course, are more brilliant, more separated, and more numerous. I fear that no amount of optical power will make these objects better known to us, though perhaps exact measurements may bring out something.

 

Thomas William Webb: Beautiful round nebula diam. 5' or 6', showing with 3 7/10 in. a granular aspect, the precursor of resolution. With 9-in. spec. resolution evident the margin seems to diffuse itself away, probably in rays. JH [John Herschel] compares it with a heap of fine sand, and considers it to be composed of thousands of 15mg. stars. Sm. [Smyth] observes that "This magnificient ball of stars condenses to the centre and presents so fine a spherical form, that imagination cannot but picture the inconceivable brilliance of their visible heavens, to its animated myriads."

 

John Herschel, General Catalogue: GC 4678: GC 4678 = h 2125 = M2 = Lalande 41928.
RA 21h 26m 12.5s, NPD 91d 26' 37.2" (1860.0) [Right Ascension and North Polar Distance]
!!; Glob. Cl.; B; vL; g, pmbM; rrr; st eS. 19 observations by W. & J. Herschel.
Very remarkable, globular cluster, bright, very large, gradually pretty much brighter toward the middle, well resolved, stars extremely small [faint].
Remark: Figures in P.T. 33 [JH 1833], plate viii, No. 88, and PT 44 [Lord Rosse 1844], plate xviii, No. 88.

 

William Huggins: [Phil. Trans. Roy. Soc., Vol. 155 (1865), p. 39-42; here p. 40]
"[GC] 4678, 2125 h. 2 M. Bright cluster, well resolved."
This cluster gave a continuous spectrum.

 

John Louis Emil Dreyer: NGC 7089 - NGC 7089 = GC 4678 = h 2125; Maraldi, M 2 = Lalande 41928.
RA 21h 26m 15s, NPD 91d 26.5' (1860.0) [Right Ascension and North Polar Distance]
!!, Glob. Cl., B, vL, gpmbM, rrr, st eS; = M2
Very remarkable, globular cluster, bright, very large, gradually pretty much brighter toward the middle, well resolved, stars extremely small [faint].
Remark: Figures in P.T. 33 [JH 1833], plate XVI, No. 88, and PT 44 [Lord Rosse 1844], plate XVIII, No. 88.

 

John Ellard Gore: The Observatory, Vol. 25, pp. 264-269, here p. 265.]
M. 2. R.A. 21h 28m.3, S 1d 15'. - In Aquarius, about 5 deg north of the star Beta Aquarii. It is a globular cluster of 5' or 6' in diameter. Sir John Herschel compared it to a heap of white sand; and Admiral Smyth says: "This magnificient ball of stars condenses to the centre and presents so fine a spherical form that imagination cannot but picture the inconceivable brilliance of their visible heavens, to its animated myriads." But that each of these points should have planets revolving round them seems very doubtful. Sir William Herschel with his 40-feet telescope could see the individual stars even in the centre of this cluster. A photograph by Dr. Roberts, taken in 1891, shows the centre of the cluster involved in dense nebulosity, and he thinks that it was probably eveolved from a spiral nebula. The stars composing the cluster are very faint, probably not above the 15th magnitude. Seen as a star it was measured at Harvard Observatory as 7.69 magnitude. Assuming these magnitudes as correct, I find that the cluster contains about 800 stars.

 

Camille Flammarion: [L'Astronomie. Revue de la Societé Astronomique de France, November 1917. P. 385-400, here p. 398-399. With a photo and a drawing] M.2. Aquarius. Star cluster.
Messier's Description:
"Nebula without star, in the Water Bearer. The center is brilliant, and the light surrounding it is round; it resembles the beautiful nebula which is situated between the head & the bow of Sagittarius [M22]. It is seen very well with a telescope of 2 feet [FL]. Placed below the parallel [same Dec] of Alpha Aquarii, M. Maraldi has seen this nebula in 1746 while observing the comet which appeared that year. - Diameter 4'."
Added in the margin: "No. 53 of the Berlin tables."
This nebula "without stars" with the telescope of Messier is now resoved in countless stars.
Observed by the two Herschels, Smyth, d'Arrest, Schoenfeld, lord Rosse, Secchi, etc. In his pittoresque language, d'Arrest qualifies it: "infinita stellularum circumlata congregies." [] It is composed of stars of 14th magnitude and fainter, as difficult to count as the grains of sand on a beautiful sunny beach.
These thousands of miniture [very faint] stars resemble a pale star of 7th magnitude. This is star number 41928 of the Catalog of Lalande, who observed it on September 5, 1795, without indicating its stellar magnitude, and with nebulosity. In my equatorial, it has always produced the effect of a pale image of the splendid Hercules cluster [M13]. - D'Arrest has estimated its diameter between 180" and 200".
It has been photographed, with the preceding [M1], at the Observatory of Juvisy, by M. Benoit in 1902 and by M. Quénisset in 1911. We have observed it in the last September and October; the photograph reproduced here has been taken by M. Quénisset on October 18 with the Viennet objective lens (exposed 2h 5m) and I have made the drawing on October 6; the variable star of which we have spoken was near its maximum (12th magnitude bright). Our drawings were made at the equatorial of 0m 24 [24 cm]; with an eyepiece of magnification 145.
I won't come back to the description I have published of this nebula in Les Etoiles [The Stars]; but I will recall the very careful observation and the drawings which our colleague M. Chèvremont has given in the Bulletin of 1898 (p. 90), such that the discovery he made of a curious variable star, oscillationg between the 12th and the 14th magnitude, in about 30 days. It is this star which is seen on its border in the photograph, to the right, or at the East. We have continued recently this curious variation, comparing this with the other stars of the same cluster.
In my booklet of observations, I find at the date of September 16, 1889: "Admirable stove of dust of condensed gold. Elongated from West to East".

 

Heber Doust Curtis: [Descriptions of 762 Nebulae and Clusters photographed with the Crossley Reflector. Publ. Lick Obs., No. 13, Part I, p. 9-42]
NGC 7089, RA=21:28.3, Dec=- 1:16. M. 2. Fine globular cluster 7' in diameter. 8 s.n

 
 
 
 
 
 
 
 
 
       
 
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