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(IAAC) Obj: NGC 6804 (PK45-4.1, HVI-38, PNG45.7-4.5) - Inst: 17.5" f/4.5 dob
Observer: Lew Gramer; Steve Clougherty
Your skills: Intermediate (some years); Advanced (many years)
Date/time of observation: 2220 Local, 17 Sep 2001
Location of site: ATMoB Clubhouse, Westford MA USA (42oN, 86m elev)
Site classification: Suburban
Sky darkness: 4+ <Bortle Scale (9 worst)>
Seeing: 8 <1-10 Seeing Scale (10 best)>
Moon presence: None - moon not in sky
Instrument: 17.5" f/4.5 dob
Magnification: 90x, 222x, 285x, 500x
Filter(s): None. UHC.
Object(s): NGC 6804 (PK45-4.1, HVI-38, PNG45.7-4.5)
Category: Planetary nebula.
Class: 4+2
Constellation: Aql
Data: Mag 12.2 14.23m*; size 63"x50" irreg
Position: 193135.43 +091330.6
Description:
NGC 6804 is one of a startling number of interesting Planetary
Nebulae, within the body of Aquila the Eagle. It can be quickly
found at the NW vertex of a right triangle with Altair (Alpha Aql)
and Mu Aql, lying just 11' SW of mag 7 white finder star HD 184061,
about 2o NNE of Mu. The PN appears readily as a non-stellar object
at lower power even sans nebula filter, though the filter helps.
--
At all magnifications up to 285x, our initial impression of this
unusual PN was of an irregular "peanut" bipolar shape, with dual
(somewhat irregular) lobes oriented to SE-NW. However, at highest
power, especially with the UHC filter, both observers immediately
noted a broad-tailed "comet" shape to the nebulosity! Note that the
"comet" tail essentially replaced the bipolar shape which our minds
filled in for us at lower powers: the tail appeared to fan out from
a bright, loose "coma" of nebulosity on the SE edge, broadening into
a "tail" which swept out at least a 60 degree angle, from W to NNW.
The "tail" was perhaps an arcminute long, and engulfed three bright
stars near the center and the NE edge of the whole nebula. Most
interestingly, no hint of annularity was noted in NGC 6804 at any
of these powers, with or without the UHC. Perhaps if we had tried
an OIII, yet another view of this little blob would have appeared?
--
A near-central star was readily seen at all powers, being easiest
at 285x with no filter. Finally, only at higher powers (especially
285x) and only with the UHC filter, a hint of an outer halo ring
was noted by one observer (me) but not the other. This outer arc,
if it existed, lay out about twice the radius from center of the
bright inner nebula, and even with concentrated averted vision it
could only be glimpsed E and N of the main nebula. Does NGC6804 in
fact have a halo?? The DSS Red and Blue plates both fail to show
any, though there may be the merest hint on the Blue Survey plate.
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