The Caldwell Objects

96
96
Southern Beehive
NGC 2516
Type: Open Cluster
Con: Carina
RA: 07 h 58.0 m
Dec: -60° 45'
Mag: 3.8; 3.5 (O'Meara)
Diam: 22'
Dist: 1,300 light-years
Disc: Abbe Nicolas Louis de Lacaille,
included in his 1755 catalog
J. HERSCHEL: An orange-
coloured star 8th magni-
tude, in middle of a large and magnificent cluster of
perhaps 200 to 250 stars [of] 8[th to] 16thmagnitude].
Many of the [brighter] magnitudes, and really a superb
LIKE RIVETS, BRIGHT OPEN CLUSTERS SEEM TO
fasten the Milky Way to Carina, the Keel of the
Ship Argo. And among the most prominent is
NGC 2516. This 4th-magnitude cluster lies just
3¼° southwest of Epsilon (ε) Carinae (Avior), the
2nd-magnitude star marking the foot of the False
Cross; the long axis of the Cross points almost
right to it. Abbe Nicolas Louis de Lacaille
discovered the cluster during his pioneering
southern-sky survey. It is the third Class II object
(nebulous clusters) in his 1755 catalog, and he
recorded it as a "very close group of 10-12 stars."
(The "nebulosity" in this case was not dust or gas
but unresolved starlight.) lohn Herschel saw
"perhaps 200 to 250 stars" centered on an orange
8th-magni-tude star.
NGC 2516 is an easy naked-eye target. It is
sometimes mistakenly referred to as the
Southern Pleiades, but that name has already
384
object. Very visible to the naked eye. (h 3111)
GC / NGC: Cluster, very bright, very large, pretty rich, stars of
magnitude 7 to 13.
been claimed. IC 2602 (Caldwell 102) — also in
Carina, nearly 20° to the east-southeast — has
been known as the Southern Pleiades ever since
Lacaille commented on its similarity to that
northern wonder.
When I surveyed the literature on NGC 2516,
I discovered a trend: the cluster's reported
angular size has been diminishing over the years.
In his Celestial Handbook, Robert Burn-ham Ir.
describes NGC 2516 as a "brilliant group, easily
visible to the naked eye, with more than 100 stars
scattered over a field 1° in diameter." The first
edition of Sky Atlas 2000.0 (some versions of
which mislabel the cluster as NGC 2561)
represents this view fairly well, showing the
cluster as a 1°-wide circle centered on a dense
core of starlight; the circle extends toward a row
of three stars to the northeast but includes only
the two southernmost members of that row.
Indeed, when I first
Deep-Sky Companions: The Caldwell Objects