Messier 102

An article on the controversary by Hartmut Frommert

      102. Nebula between the stars omicron Bootis and iota Draconis:
           it is very faint, near it is a star of 6th magnitude

                          Messier in Connaissance des Temps for 1784, p. 267

Charles Messier compiled his `Catalogue of Nebulae and Star Clusters' during the years 1758 to 1781 (or 1782 if one counts the last additions by his colleague Pierre Mechain, which are contained in most modern versions of the catalog). Contrary to prior and contemporary observers who had a large number of errors (nonexistent objects) in their lists, the entries of his catalog correspond to actual astronomical objects in all cases, perhaps with one exception, his entry number 102 (there are positional errors for 3 other objects, M47, M48, and M91, which could be figured out by the time).

For this object (M102), Messier gives above description together with M101 and M103 as communicated to him ``through M. Mechain, which M. Messier has not yet observed.'' He gives no position for M102 (and M103).

Shortly after the publication, some three or four years after the entry was made, Pierre Mechain retracted his discovery and claimed that the observation was an error, a duplicate observation of M101, and a star chart error of Messier. In a letter to Bernoulli he wrote:

      On page 267 of the ``Connaissance des Temps for 1784'' M. Messier
      lists under No. 102 a nebula which I have discovered between omicron
      Bootis and iota Draconis: this is nothing but an error.  This nebula
      is the same as the preceding No. 101.  In the list of my nebulous
      stars communicated to him M. Messier was confused due to an error in
      the sky-chart.

Kenneth Glyn Jones [1], and even more definite, Owen Gingerich in his contribution to Sky & Telescope [3] (reprinted in Mallas/Kreimer's Messier Album [2]) regard this issue as solved, in the sense that M102 is a duplication of M101. One could easily join this conclusion, as the discoverer himself admitted a fault and retracted.

However, there remain some doubts and arguments which still allow for other possibilities, as also Kenneth Glyn Jones admits. First of all, both Mechain and Messier were very careful observers, indicated by the fact that M102 is the only possible "non-object" left in the catalog, and only for 3 further objects there were positional errors. Also, as the descriptions for M101 reads:

March 27, 1781. 101. 13h 43m 28s, +55deg 24' 25". Diam. 7'. Nebula without stars, very obscure and pretty large, between 6' and 7' in diameter, between the left hand of Bootes and the tail of Ursa Major. Difficult to distinguish when graticule lit.

it appears not necessarily obvious that this is the same object as M102, with the description given above. Also, Mechain's ``retraction'' occured about 3 years after the ``discovery'', giving room for speculations anyway, and it was never published in the Connaissance des Temps, where Messier's catalog and supplements were first printed. Messier personally had added by hand a position to M102, which both Owen Gingerich and Kenneth Glyn Jones claim as erroneous ``because there is no obvious object''. As Messier was certainly a careful observer, he probably has seen `something', but maybe he did a reduction error again. Might it be that he found another object, one of the candidates discussed below, a comet, or even some completely other ?

At last, there are at least two candidates, the more probable being NGC 5866, near the position Mechain describes; wouldn't one know of his letter mentioned above, today's astronomers would probably believe that this was the observed object !

To step the way down, note that omicron Bootis is about 40 degrees away and south of iota Draconis, thus (at least) one of them must be a mistype; Admiral Smyth in his `Bedford' Catalogue suggests the obvious possibility that it must read `theta' instead of `omicron' Bootis. The other possibility would be, according to J.L.E. Dreyer in Notes and Corrections to the NGC, that iota Draconis was mistaken for iota Serpentis; then M102 would be situated near the position of the faint galaxy NGC 5928, at RA 15h23.9m, Dec +18d15' (1950).

However, Dreyer's proposition of NGC 5928 can be waived with great certainty for the obvious reason that it is only a 14th mag galaxy, according to the RNGC [4], so that both Mechain and Messier could hardly have seen it with their instrumentation, even under exceptionally good conditions. Thus we can also exclude Dreyer's assumption that iota Draconis was a mistake for iota Serpentis, since there's no sufficiently bright object in that region of the sky, and are left with the possibility proposed by Smyth, that omicron Bootis was mistaken for theta Bootis.

Between those stars, about 3 degrees SW of iota Draconis, is a small group of galaxies, the brighter of which could be viewed as candidates for M102:

NGC 5866 (William Herschel's 215 H.I, John Herschel's 1909), the brightest of the group at 10.0 mag vis.
NGC 5879 (W.H. 757 H.II, J.H. 1910), Smyth identified this as M102
NGC 5907 (759 H.II, J.H. 1917), a bright edge-on galaxy.
NGC 5908 (760 H.II), too faint as a candidate.

Most probably is NGC 5866, as Shapley and Davis suggest in their contribution to the PASP Vol. 29 (according to Glyn Jones).

Another fact makes NGC 5866 a good candidate for M102:
Imagine you want to find NGC 5866 with a telescope, how do you procede ? I would look for the stars iota Draconis and theta Bootis and then locate the 5.21 mag star GC 20332 (=SAO 029402) which is little more than 1 degree south and almost exactly at the same right ascension. This star is one of 5 in the rectangular region between RA/Dec limits given by the two stars and listed in Becvar's catalog of stars brighter than 6.25:

                       RA (1950.0)  Dec (1950)  mag
        23 theta Boo   14h23m48.8s  +52d04'52"  4.06
        GC 19627          30 56.9    55 37 03   5.99
        GC 19666          32 45.2    57 17 12   6.25
        GC 19742          36 40.0    54 14 19   5.52
      * GC 20332       15 04 59.9    54 44 53   5.21
        GC 20641          18 36.8    52 08 16   5.52
        12 iota Dra    15 23 48.8    59 08 26   3.47

(NGC 5866 is at RA 15h05.1m, Dec +55d57'). A misestimate of a 5.21 as 6th mag star would eventually be not too far off, so that the `6th mag star' in Messier's description might be GC 20332. Then the description matches well with that visually 10th mag lenticular galaxy, as it appears probable that Mechain perhaps wanted to describe a route to his newly `discovered' object. Another possibility is that the star mentioned is the 6.8 mag star lying only 0.4 degrees NW of NGC 5866.

However, as Mechain has disowned the discovery, one may keep the position that due to his claim, Mechain's discovery was spurious and eventually a duplicate observation of M101 as he claimed. As also Don Machholz admits, it may well be that he was correct with this statement, then there remains only the puzzle of Messier's handwritten position. To summarize:

The object that really deserves the designation "Messier 102" should be identical to one of the 2 observed by Mechain and Messier, may they be identical or not. As nobody is still alive who has witnessed them during their observation and recording, we can currently not reconstruct what they actually observed. Mechain's description gives good evidence that the object M102 could be NGC 5866, which most probably everybody would believe if he had not retracted the discovery in the letter mentioned, or if this letter had stayed forgotten. It may now depend on taste to speculate which was erroneous: The observation or the letter.

Messier 102 in the sources:

Sources claiming that "M102=M101":

Gingerich [3] and Glyn Jones [1]
Mallas and Kreimer's Messier Album [2] (quoting Gingerich [3])
Messier Chart, Messier Poster and other recent products from Sky Publishing Corporation.
Becvar, see below.
The SEDS Messier internet collection (http://seds.lpl.arizona.edu/messier/Messier.html)

Sources identifying M102 with NGC 5866:

Don Machholz in his Messier Marathon Observer's Guide [5]. Don Machholz also discusses the subject and comes to similar conclusions as the present author.
Antonin Becvar in his `Atlas Coeli, Atlas of the Heavens - II, Catalogue 1950.0', 1964 gives in the `Anagalactic Nabulae' section for NGC 5866 the alternative name M102 (p. 329 or S21). Oddly, in the `Catalogue of Messier' section on p. 339 or M3, he gives
M 102 = NGC 5866, Type S [galaxy], [No other data], Notes: `= M 101'
Perhaps this reflects the situation :-)
Hans Vehrenberg, in his Atlas of Deep Sky Splendors, claims that Owen Gingerich has added it, which I do not believe because Gingerich [3] claims the opposite.
RNGC [4], p. 273, gives M102 as alternative name for NGC 5866.
Erich Karkoschka in his Atlas. Karkoschka states in the description to chart N16 (I must translate from the German edition):
``Messier's list contains as its object 102 a galaxy [it's the first time I hear that Messier did know that - hf] near the position of NGC 5866. However, his description points to a duplication of M101 [I cannot verify this, see both descriptions given above; my impression is more that NGC 5866 might match the description - hf]. Did Messier do a mistake of 1 hour in right ascension [How, as he gave no measured position :-) - hf] ? Therefore, the designation M102 is nonunique.''
J.D. Wray, The Color Atlas of Galaxies, Cambridge UP, 1988
Nasa's extragalactic database (telnet ned.ipac.caltech.edu, login ned) has M102 as a name for NGC 5866.
Tony Cecce (CECCE_AJ@CORNING.COM) in his Twelve Month Tour of the Messier Catalog, May issue.
A data list from Finland, a/v on the internet.

Sources with other identifications:

Admiral Smyth proposes either NGC 5879 or NGC 5866. Kenneth Glyn Jones gives his description:
`A small but brightish nebula on the belly of Draco with four small stars spreading across field N of it. Doubt as to wether this is the nebula discovered by Mechain in 1781 since Messier describes it as ``very faint'', situated between omicron Bootis and iota Draconis. If omicron Bootis should be theta Bootis, this is probably the object seen by Mechain and J.H.'s 1910, being the brightest nebula of five in that vicinity.'
The problem is that John Herschel's number 1910 is NGC 5879, which is however {not} the brightest of the group; the brightest is NGC 5866.
Dreyer (NGC) oddly proposes 14th mag galaxy NGC 5928.

References:

  [1] Kenneth Glyn Jones. Messier's Nebulae & Star Clusters. 2nd edition,
      Cambridge University Press, 1991. Practical Astronomy Handbooks Vol. 2.
      1st edition 1968, Faber.

  [2] John H. Mallas and Evered Kreimer. The Messier Album. 1st edition.
      Sky Publishing Corporation, 1978 (Second revised printing 1979).

  [3] Owen Gingerich. The Missing Messier Objects. Sky & Telescope, Vol 20,
      October 1960.

  [4] Jack W. Sulentic, Tifft. The Revised New General Catalogue.

  [5] Don Machholz. Messier Marathon Observer's Guide -- Handbook and Atlas.
      MakeWood Products, P.O.Box 1716, Colfax, CA 95713, USA. 1994

Questions

Can someone provide the position which Messier added by hand to his personal copy of his catalog, and which Gingerich and Glyn Jones claimed spurious ? Anyway, it might be possible to find possible pointers to an object, one of the above candidates or another, if one takes another sign error in data reduction into account. Has Messier eventually observed a further object when checking this position (a `lost' Messier object) ?