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NGC 7293
Helix Nebula
Ben 129, ESO602-PN022, PK036-57.01
RA 22:29:37
Dec
-21° 11.5'
Planetary nebula 
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The NGC notes that it was observed by Harding,
and describes it as "remarkable, pretty faint, very large, elongated or
bi-nuclear."
Innes, in Union Obs. Circ., 1-44, p 345,
notes: “Seen in both the 3-inch and 9-inch telescopes. Large, but no
detail. Helix or ring not seen. 1917, September 13.”
Burnham calls it "remarkable, pretty
faint, very large, very slightly elongated, annular, diam. 12' with 13th mag
central star." He notes that despites its large size (12' x 16') it is
faint and has a low surface brightness. He estimates the total magnitude as
6.5. Binoculars will show the object as a large circular hazy spot, and it is
not a difficult object for a small telescope if a low power ocular is used. "Yet,"
notes Burnham, "it is said that this nebula was never observed by either of
the Herschels with their giant telescopes!" The annular appearace, notes
Burnham, similar to the Ring Nebula in Lyra, is not clearly seen visually, but
is well shown on long exposure photographs. The general structure resembles a
coil with two turns; a much smaller planetary in Draco (NGC 6543) has a very
similar pattern.
Hartung writes: "This remarkable object
... is a large rather faint annulus about 14' x 12' with a dark centre about 6'
across and a 12th mag central star. The brightest parts of the ring as N.f. and
S.p., and the faintest part is N.p. where the luminous haze is broadest and four
small stars are involved ... the nebula may be seen as a faint round haze with a
3-inch telescope."
Houston notes it has a very low surface
brightness because of its unusually large quarter degree diameter. "Nevertheless
there are reports of it being seen in 7x35 binoculars and 6x30 finders."
He notes that it has a total magnitude of 6.5, but because of its great size it
has a low surface brightness; "its pale hazy disk is often missed by
amateurs who are accustomed to seeking much smaller objects. Averted vision is
needed, and the eyepoiece field should be at least half a degree in order to
surround the nebula with some contrasting dark sky."
According to Phil Harrington, it is a real
challenge for a 2- to 3-inch binocular. It has, however, been found easily with
a 10x40 binocular, appearing as a faint spherical glow with direct vision. In "Touring
the Universe through Binoculars (Harrington, 1990) notes that "under prime
conditions, this celestial smoke ring looks like a round, hazy patch of dim gray
light. Giant binoculars hint at the cloud's subtle texture, but the central
star will remain unconfirmed. Due to its low surface brightness and large
expanse, NGC 7293 is frequently much easier to pick out in the wider fields of
binoculars than with comparatively narrow-field telescopes."
Sanford notes that it is "large (15'
diameter) but faint ... This wonderful object appears like a large, dim
smokering in 20x80 binoculars. A dark, clear night is necessary to view it
well, when it can be seen in steadily held 7x50 binoculars. In a rich-field
telescope with an O-III filter, the contrast is increased, and the object
becomes easy to see."
John Bortle (Webb Society Quarterly Journal,
January 1976) using 10x50 binoculars, estimates the visual magnitude as 7.4.
James B. Kaler ("The Amateur Scientist",
Scientific American, May 1992) notes: "The closest known planetary nebula
to the earth, it is a mere 500 light years away. Because it is so old, the
nebula is enormous. Furthermore, because it is so close, it covers a region of
sky almost half the angular diameter of the full mon . . even with binoculars,
Wyrick picked it out as a 'grayish blob' and saw a hint of its ring structure.
Using 10-inch scopes, Cadle and Mitchell clearly saw its ghostly ring set among
the stars."
Tom Lorenzin, in the e-version of "1000+
The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "7.3M;
13' diameter; N-filter helps greatly on this!; four faint stars on W side (two
NW and two SW); N-filter shows center more rarefied though 13M enter star not
visible in interior glow; visible in binoculars!."
Steve Coe, using a 17.5" f/4.5, notes: "Pretty
bright, Very large, annular at 100X. The UHC filter helps the contrast very
much. Seen as uniformly illuminated disk in 10X50 finder or binocs. The central
hole can be held steady at times, but is generally more prominent with averted
vision. There are 5 stars involved within the Helix shape. If you are looking
for a real observing challenge for your next observing session, the Helix can
supply a toughie! The picture of the Helix on page 195 in Burnham's Celestial
Handbook shows a very faint edge-on galaxy at the edge of the Helix Nebula. It
is located at the end of the Helix that opens up near a pretty bright star.
Using the 17.5" on a night I rated 9/10 at 8000 ft. in the Central
Mountains of Arizona, I could just pick it out at 300X. 13" Sentinel 8/10
11X80 easy, bright, large, round, several stars near and involved. 60X nice
view, 5 stars involved and nice double star at south edge, center darker, but no
"hole". 100X 7 stars involved, still no hole in middle, adding UHC
filter makes it a very contrasty view, much darker middle, only 5 stars
involved, but nice view. 150X best view, neby is about 60% of the field of view,
11 stars involved, several very faint, north side of nebulosity is brightest.
Adding the UHC at 150X shows the middle as very dark, but not completely free of
nebulosity at any time."
11x80: "Ill-viewed,
since the portion of sky was setting, in the light-pollution glow of
Stellenbosch, behind the mountain. The nebula showed as a delicate smudge, round
in shape. The nebulosity is unaffected by stars, and appears even; the 6-inch
shows several small stars involved. The nebula was readily seen, even on a
bright ligh-polluted background. Just to the north of the nebula lies an 8th mag
star, which is the start of a 4-star trail, ending in a 7th mag star to the
west; these stars are useful for estimating the size of the nebula; with averted
vision, I see it as about 17' across." (suburban skies, seeing 7/10,
transparency 7/10, darkness 4/10) [AS]
11x80: "Remarkable! A
bright glow, some 20' across. Small star nearby on the north-western edge,
another on the south-western edge. Had a look, also, at M33, and saw it as a
bright, round glow; just like a larger version of NGC 7293 - a formless nebulous
glow." (suburban skies, seeing 6/10, transparency 7/10, darkness 7/10, lim
mag 6.0 (naked eye, pole) [AS]
6-inch f/8.6 Newtonian: "What
an amazing sight! At least 10 arcmin across, it is a large, round ghostly glow
of light. There are several small stars enveloped in the nebulosity. A unique
and charming object." (exurban skies, Franschoek mountain pass summit,
obvious haze and thin clouds, sky fairly bright around horizon.) [AS]
Meade 8 inch, Super wide-angle 18mm
eyepiece; 36' fov: Extremely large, very faint, roundish gracious disk.
Darker to the inside with some stars, a bright one just off center to the south.
Nebula shades out brighter, with a fading north west side. Very low surface
brightness. I estimate this nebula about 20 arc minutes. At last the Helix, what
a pleasure! [MS] |
