The Caldwell Objects

80
80
Omega Centauri
NGC 5139
Type: Globular Cluster
Con: Centaurus
RA: 13 h 26 m 46 s
Dec: -47° 28' 37"
Mag: 3.7; 3.9 (O'Meara)
Diam: 55'
Dist: 17,300 light-years
Disc: Listed as a star in Ptolemy's
Almagest of 150 A.D.; probably recognized
as a "star" by sky-watchers throughout
history
J. H ERSCHEL: Diameter full 20'.
It much more than fills the field.
When the centre is on the edge of
the field, the outer stars extend fully half a radius
beyond the middle of it. The stars are singularly equal,
and distributed with the most exact equality, the con-
densation being that of a sphere equally filled.
Looking attentively, I retract what is said about the
equal scattering and equal sizes of the stars. There are
two sizes 12th magnitude] and 13th magnitude],
without greater or less, and the larger stars form rings
like lace-work on it. One of these rings, 1.5' in diame-
ter, is so marked as to give the appearance of a com-
parative darkness like a hole in the centre. There must
DROP A VISUAL PLUMB LINE 36½° DUE SOUTH of
brilliant Spica in Virgo, and you will encounter a
soft and solitary 4th-magnitude glow that looks
slightly "hairy," like the fuzzy patina of a fading
comet — even under a direct gaze. That's Omega
(ω) Centauri (Caldwell 80). Omega Centauri also
marks the northwestern corner of an isosceles
triangle that also comprises the roughly 2ndmagnitude
stars Zeta (ζ) and Epsilon (ε)
Centauri, and it is 13° northeast of Gamma (γ)
Crucis, the northern tip of the Southern Cross.
318
be thousands of stars. To the naked eye it appears as a star of
5th magnitude] or 5[th to] 4th magnitude], rather hazy. There is
a 9th magnitude] star on the S.p. [southwestern] border of it,
about 4' or 5' south of centre, and several [of] 8th magnitude]
are scattered far away. My attendant [(John South)] called up,
who saw the hole and darkness, and described it as I have done
above. On further attention the hole is double, or an oval space
crossed by a bridge of stars. Position of axis = 150°. (h 3504)
GC/NGC: Remarkable, globular cluster, ω Centauri.
How is it that the Alpha of globular clusters
became known as Omega Centauri? The answer
lies with the way early astronomers assigned
Greek letters to the stars.
The Bavarian lawyer and astronomer Johann
Bayer (1572-1625) is usually credited with the
idea of attributing letters to stars, and the Greekletter
star labels used today are known as Bayer
designations. However, as the late Sky & Telescope
editor loseph Ashbrook writes in his Astronomical
Scrapbook} the "idea of using letters to designate
stars was. . . not
Deep-Sky Companions: The Caldwell Objects