The Caldwell Objects

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Saturn Nebula; Venus Nebula;
Ghost of Saturn Nebula
NGC 7009
Type: Planetary Nebula
Con: Aquarius
RA: 21 h04 m 10.8 s
Dec: -11° 21' 49"
Mag: 8.0
Dim: 44" X 23"
Dist: 1,400 light-years
Disc: William Herschel, 1782
W . HERSCHEL: [Observed 7 September 1782] Very bright, nearly
round planetary disk not well defined. (Η IV-1)
GC / NGC: A magnificent object, planetary, very bright, small,
elliptic.
O N THE EVENING OF A UGUST 29, 1780,
Pierre Mechain, Charles Messier's contemporary
and rival comet hunter, discovered a faint glow
in Aquarius 4° southwest of 4.5-magni-tude Nu
(ν) Aquarii. Messier searched for Mechairis find
the following October (on the evenings of the 4th
and 5th) and determined its position relative to
Nu Aquarii. Now known to be a globular cluster,
this object became the 72nd in Messier's growing
list of non-comets. On those same two evenings,
Messier discovered a "[c]luster of three or four
faint stars, which, at first glance, resembles a
nebula." Again Messier determined the new
object's position relative to Nu Aquarii, and this
tiny asterism became the 73rd object to enter his
catalog. The irony of these discoveries and their
follow-up observations is that about 1¼° due
west of Nu Aquarii is one of the heavens'
brightest planetary nebulae — NGC 7009. And it
entirely escaped both Messier's gaze and
Mechairis.
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But this is not surprising. Although NGC 7009 is
bright, it is also small (its brightest part spans
only 23"), and it can be easily mistaken for a star
at low power, especially when seen through a
small telescope. The nebula did not fool William
Herschel, though; he discovered it in 1782,
finding it "very bright." He also classified the
object now known as NGC 7009 as a planetary
nebula because it was "nearly round," like a
planet, and bore magnification well, like a planet.
However, the nebula's hallmark ringlike
extensions remained undetected until Lord Rosse
(William Parsons, third Earl of Rosse) scrutinized
the nebula with his 72-inch reflector. In his 1850
paper, "Observations on the Nebulae," Rosse
described NGC 7009 as having a fairly uniform
luminous disk with "ansae which probably
indicate a surrounding nebulous ring seen
edgeways." Indeed, as Robert Burnham Jr. notes
in his Celestial Handbook "Rosse's drawing
portrays the nebula with a somewhat greater
degree of symmetry and
Deep-Sky Companions: The Caldwell Objects