The Missing Messier Objects
Unlike his contemporary and earlier colleagues,
Charles Messier was such a
careful observer that all objects in
his catalog (possibly with the exception
of M102) actually exist and could be identified with
real celestial objects. However, he was not always an error-free recorder and
data-reducer, making some few mistakes which have hidden 4 objects for more
than a century, so that they were missed.
The missing objects are
M47 was missed because Messier did a sign
error during the reduction of positional data. He computed the position of
this cluster from the differences to the star 2 Puppis (2 Navis in Messier’s
time), but mistook the sign of the right ascension difference. This fact was
recognized by T.F. Morris of the RAS of Canada in 1959, after Oswald Thomas
had identified it correctly as NGC 2422 in his 1934 book Astronomie.
Previously, John Herschel had given the wrong position a number in his
General Catalogue, and following him, J.L.E. Dreyer a NGC number, NGC 2478,
although at that position there’s no object at all.
M48 is not so obvious, but as (the same
astronomer) T.F. Morris pointed out in 1959, the only object matching Messier’s
description in this celestial area is NGC 2548, which is now generally
recognized as M48. It lies at the same right ascension, but almost exactly 5
degrees south of Messier’s position. The reasons for this error will probably
remain obscure unless Messier’s lost observing books of this period should
come to light one day.
M91 was much more difficult to reconstruct;
finally, Messier had measured the position of this galaxy from the previously
discovered M89, but thought he had used M58, as the amateur astronomer
William C. Williams of Texas had found out and thus identified M91 with
NGC 4548, now generally accepted and quite safe. Previously, it had been
assumed that M91 might be the 12 mag galaxy NGC 4571, the nearest to
Messier’s position – unlikely but not totally impossible. Many sources also
held the version that it was actually a comet that fooled Messier – even more
unlikely with regard to the fact that Messier was the comet specialist,
and Owen Gingerich had brought up the hypothesis that it might be a duplicate
observation of M58.
M102 finally could not be cleared up with
certainty up to now. At last, there are still two possibilities open:
It may be a duplication of M101, as its discoverer
Pierre Mechain believed when he wrote a letter to Bernoulli in Germany two
years later, but on the other hand, its description in Messier’s catalog
(which was actually Mechain’s description) matches well with
Moreover it may be that Charles Messier has observed this object when
measuring the position of M102 which he wrote by hand into his personal copy
of the catalog, but did a data reduction error again, plotting it exactly 5
degrees west (preceding) of its true position in right ascension.
The present author has discussed this topic and
thinks it depends on taste to believe which was erroneous: the observation or
the letter, or if Messier’s possible observation justifies the designation
`M102′ for this object.
To summarize: The four missing Messier objects were probably missed because of
errata of Messier in data reduction, in detail one sign error (for M47), one
mistaken comparison object (for M91) and one or, probably, two “grid” errors,
i.e. positions which are exactly 5 degrees off (for M48 in declination, for
the M102 candidate NGC 5866 in right ascension), which is the grid tick width
in the charts he used
(see e.g. this example)
and can thus be explained by wrong looks or labels.
Last Modification: 25 Jan 1998, 14:50 MET