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[M 2]

Messier 2

Observations and Descriptions

Discovered by Maraldi on September 11, 1746.
Independently rediscovered by Messier on September 11, 1760.

Messier: M2.
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')

[Handwritten note in Messier's personal copy:] `No. 53 of the Berlin tables'

[Note on the Chart, Mem. Acad. for 1760, p. 465, Plate 12, Planche II]
Beautiful Nebula, Discovered in 1746.

[Mem. Acad. for 1771, p. 436-437 (first Messier catalog)]
On September 11, 1760, I discovered in the head of Aquarius a beautiful nebula which doesn't contain any star; I examined it with a good Gregorian telescope of 30 pouces focal length, which magnified hundred four [104] times; the center is brilliant, & the nebulosity which surrounds it is round; it resembles quite well the beautiful nebula which is located between the head and the bow of Sagittarius: It extends 4 minutes of arc in diameter; one can see it quite well in an ordinary telescope [refractor] of 2 feet [focal length]: I compared its passage of the meridian with that of Alpha Aquarii which is situated on the same parallel; its right ascension was derived at 320d 17', & its declination at 1d 47' south. In the night of June 26 and 27, 1764, I reviewd this nebula for a second time; it was the same, with the same appearances. This nebula can be found placed in the chart of the famous Comet of Halley, which I observed at its return in 1759 (b).
(b: Ibid. [Mem. Acad.], year 1760, page 464.)
Since the discovery of this nebula in 1760, being curious to survey all which had been published about the Comets; I found in the Volumes of the Academy for the year 1746, a Memoir by M. Maraldi, on the Comet seen that year at Lausanne by M. de Chéseaux: M. Maraldi reports in this Memoir the discovery of this same nebula, which he noticed for the first time on September 11, when observing that Comet. Here is what he said: "on September 11, I observed a nebula of which the right ascension is 320d 7' 19", & the declination of 1d 55' 38" south, almost on the same parallel where the Comet would be; this nebula is round, well terminated & brighter in the middle, it occupies about 4 or 5 minutes of a degree, & is not surrounded by any star, but it has one at a rather great distance; one doesn't see any in the whole field of the telescope, which appears to me quite singular; for the majority of stars which are called nebulae are surrounded by a great number of stars; what has made judge if the whiteness which one discovers there, is the effect of the light of a cluster of stars too small [faint] for being perceived with the largest telescopes: I first took that nebula for the Comet."
[p. 454] 1760.Sep.11. RA: 320.17. 0, Dec: 1.47. 0.A, Diam: 0. 4. Nebula without stars, in the head of Aquarius.

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."

Bode: Bode 70
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."

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

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

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 Herschel (1833): h 2125.
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.

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.

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.

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.

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.

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.

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.

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".

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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