The Caldwell Objects

49 & 50
onto Indonesian soil. We see the cluster quite
clearly because the dust and gas at the Rosette's
center have been forced away by strong winds
from the cluster's hot, young stars. Blowing at
supersonic speeds of 10 km per second, these
winds have hollowed out the large cavity we see
at the center of the nebula, creating an interstellar
bubble. The powerhouse behind this activity
appears to be a star 50 times as massive as the
Sun and 1 million times as luminous. The cavity
will continue to expand until the stars are free of
nebulosity. Data from the now-defunct Infrared
Astronomical Satellite, or IRAS, have yielded
direct evidence of ongoing massive star
formation. Furthermore, at the northeastern
border of the Rosette Nebula, a large supernova
remnant, the Monoceros Loop, has been found.
Thus all stages of star formation, from the earliest
to the latest, are present in this region.
For centuries the Rosette and its attendant
cluster have been a historical enigma of sorts.
Experienced observers may note that the nebula's
NGC designation in the table on page 194 —
NGC 2237-8,46 — differs from the more popular
usage of NGC 2237-9, 46. There is a reason for
that, as we shall see. But first let's look at this
remarkable object's history.
Some sources credit England's first Astronomer
Royal, John Flamsteed (1646-1719),
with discovering the star cluster now called NGC
2244 in 1690 or thereabouts. However, this
appears to be a simple case of "close but no
cigar." A look at Flamsteed's 1729 Atlas Coelestis
reveals a single 6th-magnitude star, later
designated 12 Monocerotis, near the position of
NGC 2244. But 12 Monocerotis does not belong
to NGC 2244; it is a foreground star superposed
on the southeastern limb of the cluster's densest
portion. The brightest true cluster member shines
at 7th magnitude and hence would have been too
196
faint for Flamsteed's charts. Although the Rosette
cluster has a total integrated magnitude of 4.8, its
light is spread across an area of sky equal to that
of the full Moon. For Flamsteed to receive credit
for discovering the cluster, he would have had to
make note of stars other than 12 Monocerotis, or
of a general fuzziness near that star. To my
knowledge Flamsteed did neither. The irrefutable
discovery of the Rosette's cluster, then, belongs to
William Herschel, who found it in 1784 during
one of his now-famous sweeps of the heavens.
Some works credit John Herschel with the
cluster's discovery, but John merely rediscovered
it 30 years after his father. Contrary to popular
belief, neither William nor John Herschel saw any
nebulosity around the cluster. Why they didn't
remains a mystery.
An even greater mystery is that the renowned
18th-century French comet hunter
Charles Messier obviously missed (or ignored)
the Rosette and its cluster during his sweeps;
neither object is listed in his catalog. Certainly he
hunted this region for comets, because the 50th
object in his catalog, M50, is an open cluster in
Monoceros, and it is 4° farther south, and a
magnitude fainter, than NGC 2244. Messier
chanced upon M50 (which had already been
noted by at least one other astronomer) while
observing the comet of 1772, so, at least for him,
it was an accidental find. As for the Rosette
cluster, Messier certainly would not have
mistaken it for a telescopic comet. But what
about with the naked eye? Neither Messier nor
the Herschels noted this apparent fuzzy nakedeye
patch in the sky.
At times like this I have to wonder if perhaps
Messier and the Herschels were great
telescopic observers but not particularly keen
naked-eye skywatchers. I raise this point because
most observers today claim to have little trouble
seeing the Rosette cluster as a
Deep-Sky Companions: The Caldwell Objects