Messier 102

An article on the controversy 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) in the published version of the catalog (although he has added positions from hand in his personal copy, see below).

About two years after the entry was made and published, 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, dated May 6, 1783, 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. In addition, Mechain's ``retraction'' occured over 2 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, although both astronomers became associate editors of this periodic publication: Messier in 1785 and Mechain in 1786.

Moreover, Messier had added by hand a position for M102 to his personal copy of the catalog, which both Owen Gingerich and Kenneth Glyn Jones have claimed to be erroneous ``because there is no obvious object''. As Messier was certainly a careful observer, it is probable that he has seen `something', but maybe he did a reduction error again. The question arises if he found another object, either one of the candidates discussed below, a comet, or even some completely other one ? We will come back to this question later, as it suggests a very interesting possibility.

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

The most probable candidate is NGC 5866, as was first suggested by Harlow Shapley and Helen Davis in their article `The Messier Catalogue' in the PASP Vol. 29, and also printed in The Observatory Vol. 41 (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 5.25 mag star GC 20332 (= HD 134190, SAO 29407) 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' for 1950.0). A misestimate of a 5.25 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, though perhaps less probable, possibility is that the star mentioned is the 6.8 mag star HD 133666 (SAO 29393) lying only 0.4 degrees NW of NGC 5866. The good match of Mechain's description with this galaxy suggests that this may have been the object he had seen in his discovery observation.

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.

For me, the author of this article, some light came into this mystery when Dr. Don Greeley communicated to me the handwritten positions Messier had added to his personal copy of the catalog printed in the Connaissance des Temps for 1784. He points out:

The positions in Messier's catalog were very faded and difficult to interpret. It was necesary to make a copy of that page so dark that the printing on the page behind it showed through. I made a slide of the page and when projected on a flat white wall showed that M102 was "14.40" in RA and "56." in Dec. M103 was much harder to see but is probably "1.20" in RA and "61." in Dec. Now they must be corrected for precesion for modern charts.

The acuracy of Messier's values is probably indicated by the rough decimals, but for the following considerations I suppose them more acurate as they really are. When precessed to modern times, there is little surprise that the position for M103 becomes RA = 1:34.6, Dec = +62.1 (2000.0), close (little more than 1 degree north and very little east) to the correct position of this cluster, which is RA = 1:33.1, Dec = +60.7. Messier's position of M102 becomes

RA = 14:46.5, Dec = +55.1 (2000.0).

In accordance to the claims of Owen Gingerich and Kenneth Glyn Jones, there is actually no striking object close to this position in the sky. It is however interesting that the position lies between the stars iota Draconis and theta Bootis (so that at least it is apparently validated that the "omicron" in the description is a typo). On a closer look, one also fails with a sign error in a positional difference, as it had occured for M47, or a parallel shift due to taking a wrong reference star or object as for M91. But, and that is apparently most interesting, the position is almost exactly at the correct declination for NGC 5866 and M101, and it is almost exactly 5 degrees (20 min) west (preceding) of NGC 5866 in right ascension (is is also roughly 10 degrees east of M101, but much less acurately; the 2000.0 position of NGC 5866 is RA 15:06.5, Dec +55.7, while that of M101 is RA 14:03.2, Dec +54.3). The particular interest connected with this arises from the fact that another missing object, M48, was also measured nearly exactly 5 degrees false (in that case in declination, though). A look in the sources suggests that Messier has normally used sky charts with grids of lines every 5 degree, as e.g. his chart showing the path of the comet of 1779. Then a deviation of exactly 5 degrees may have several simple reasons: A wrongly labelled chart, an erroneous look on the neighboring label, a wrong count to an un-numbered tick, etc.

Therefore, in the opinion of the present author, it appears probable that Charles Messier has observed NGC 5866 when he measured the position of M102 (which he could probably locate without much difficulty because of Mechain's acurate description), but due to some reductional error, plotted it exactly 5 degrees west (preceding) of its correct position.

To summarize:

The object that really deserves the designation "Messier 102" should be identical to one of the two 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. Moreover, Messier has probably observed NGC 5866 and taken it for M102, but again made an error in data reduction. Once more, it is a question of taste if these facts entitle the lenticular galaxy NGC 5866 to bear the designation ``M102".

At least, observers who want to go for sure that they observed all Messier objects should thus turn their telescopes to aim NGC 5866. They will be rewarded by quite an easy, beautiful object.

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.
Before the integration of this article, the SEDS Messier internet database had joint this view; now we have adopted the arguments of the discussion here.

Sources identifying M102 with NGC 5866:

Harlow Shapley and Helen Davies, in `The Messier Catalogue', published in PASP Vol. 29 (1917) and also in The Observatory, No. 41, probably first suggested that M102 could be NGC 5866. They quote a letter of Prof. Bailley:
Messier's list comprises one hundred and three objects. For all of them, positions are given, except for 102 and 103. For these only the descriptions are given, as follows:
102. Nebuleuse entre les etoiles Omicron du Bouvier and [sic!] Jota du Dragon; elle est tres-faible; pres d'elle est une etoile de la sixieme grandeur [Nebula betrween the stars Omicron Bootis and Jota Draconis; it is very faint; near it is a star of sixth magnitude].
103. Amas d'etoiles entre Epsilon et Delta de la jambe de Cassiopeia [Cluster of stars between Epsilon and Delta Cassiopeiae].
By a star chart, or the sky, you will see that, taken as it stands, no object could be well selected for M102, since Omicron Bootis is too far from Jota Draconis. If, however, Omicron is a misprint for Theta, it becomes intelligible, and M102 is perhaps N.G.C. 5866, altho in Norton's Atlas it is apparently identified as N.G.C. 5979. On our photographs, however, N.G.C. 5866 appears to be the brightest object in this region.
Shapley and Davis remark that "The visual observations of these neighboring nebulae by the Herschels show N.G.C. 5866 much the brighter, and its identity with M 102 can be accepted as quite probable."
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. This claim is possibly based on a report by Paul Ahnert in his Kalender für Sternfreunde 1962, p. 164-166. It seems that this - presumably erroneous - claim also found its way into recent work such as Harvard Pennington's The Year-Round Messier Marathon and George R. Kepple's and Glen W. Sanner's The Night Sky Observer's Guide (Vol. 2).
RNGC [4], p. 273, gives M102 as alternative name for NGC 5866.
Landolt/Börnstein, in their monumental encyclopedia, list NGC 5866 as M102 in their Volume 6, 1, chapter 9, where they have a table of NGC numbers of Messier's galaxies.
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 (NED, also telnet ned.ipac.caltech.edu, login ned) has M102 as a name for NGC 5866.
Tony Cecce in his Twelve Month Tour of the Messier Catalog, May issue.
A data list from Finland, available on the internet via anonymous ftp: ftp://ftp.funet.fi/pub/astro/dbases/deepsky/messier.dat.

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 and William G. Tifft. The Revised New General Catalogue 
      of Nonstellar Astronomical Objects. The University of Arizona Press,
      1973.

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

Acknowledgements:

The author is grateful to all who have encouraged him to write this article and given helpful comments (especially Tony Cecce and Guy McArthur), and in particular to Dr. Don Greeley who communicated the handwritten positions of M102 and M103.

Copy of the original M102 article as posted on Usenet in May 1995

Hartmut Frommert
Christine Kronberg
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Last Modification: February 20, 2000