The Caldwell Objects

This entry is obviously in error, because
Omicron Bootis and Iota Draconis lie nearly 40°
apart — making them far too imprecise a marker
for visual stalwarts like Messier or his
contemporary, Pierre Mechain, who purportedly
discovered this nebulous object. So what is
M102?
One could reasonably argue that the star Theta
(θ) Boötis was misread as Omicron (o) Bootis,
since an observer can find several faint galaxies
between Iota Draconis and Theta Bootis, which
lie about 11° apart, and the brightest and most
conspicuous of these galaxies is NGC 5866. This
explanation is enticing, but there is no need for it,
nor for any other theories on Μ102 (though
cooking up such theories remains popular to this
day, probably because everyone enjoys a good
mystery). For Mechain explained the mystery of
Μ102 in a letter that he published in the 1786
Berliner Astronomisches Jahrbuch:
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.
Simply put, Μ102 is not a mystery unless
you want it to be; in light of the historical evidence,
NGC 5866 should lose any association
with the name "M102."
Certainly one can wonder why neither
Messier nor Mechain discovered NGC 5866,
because it is a wonderful blaze of light. In the
Genesis at 23x the galaxy is immediately obvious
as a condensed elliptical glow with white
winglike extensions. At higher powers the
galaxy shows a prominent ring with a tight
core that gradually focuses to a pinpoint. Overall,
NGC 5866 is a much more dramatic object than
M99 or Μ100, or Μ101, for that matter. So it is
understandable why some amateur organizations
include NGC 5866 in their Messier
Catalogs and Marathons. We like to think of
Messier's catalog as being chock full of the sky's
most magnificent objects, so why not insert the
meritorious NGC 5866 into that gap between
M101 and M103?
Unfortunately, creating a "hit list" of the sky's
most wonderful deep-sky objects was not
Messier's intent. His catalog was drafted to
document objects that masqueraded as comets,
objects that for the most part had been swept up
during comet hunts. Indeed, NGC 5866 cannot be
singled out, because Messier and Mechain did
not include other conspicuous deep-sky objects,
as the Caldwell Catalog amply demonstrates.
Not until 1789, when William Herschel was
methodically sweeping the heavens with his
telescopes, did anyone unambiguously
document an encounter with the object now
known as NGC 5866. We should be careful not to
let our modern desires interfere with history.
5
N G C 1 5 2 8
T y O p e C : n l u s t e r
C o P n e : r s e u s
RA: 04 h 15.3 m
Dec: +51° 13'
Mag: 6.4
Diam: 18'
Dist: 2,400 light-years
During the cool winter nights of the Northern
Hemisphere, our galaxy's outer arms arc gracefully
over the North Celestial Pole like a garden
trestle covered in snow. Night after night, the
Twenty Spectacular Non-Caldwell Objects 433