Donald R. Ferguson of Houston, Texas, contributed an extremely
detailed and informative article -- "Planetary Nebulae from the City" --
in the April, 1995 "OBSERVER'S PAGE" of SKY & TELESCOPE magazine.
Ferguson must be an absolutely wonderful observer, because he managed
to discern detail of some remarkably faint planetaries, using a 3.5"
aperture Questar (tm) and a Lumicon O-III(tm) filter, that at least in
a few cases during the 1990s had eluded my earliest searches in the
darker skies of the mountains south of San Jose.
By shielding his telescope from direct streetlight glare with a
large patio umbrella, and covering his head with a dark drape, this
gentlemen seems to have squeezed just about every photon that fell on
the tiny Questar mirror into his sensitive eye. Not only did he manage
to 'bag' tiny (nearly stellar) planetaries with high surface brightness
ratings, but also he was able to detect the the soft glow of NGC-7008,
the faint visible traces of the large, low-brightness Helix nebula, and
the extremely pale halo of gas around Campbell's Hydrogen Star (the last
of which I could not personally verify until numerous attemps over a year
and a half during observing sessions under a much darker high-altitude
rural site, using 17.5", 8", and 6" aperture scopes.)
During the late summer and fall of 1995, I utilized the Ferguson list
of planetaries for some very rewarding observing sessions. Most of the
items had been viewed by me in the past, but many of the smaller (nearly
stellar) ones had previously seemed not worth the effort of tracking down.
But aided by a new motorized equatorial mount that permitted high-magni-
fication scrutiny (an absolute MUST for easy detection of tiny faint
planetaries), I attempted to study the objects that were favorably
placed during the current seasons.
General comments are given below about most of the more interesting
and least-viewed of the planetaries. An accompanying graphic (above)
includes some of my eyepiece sketches, made with the 8-inch aperture
f5.2 Newtonian (which offers an inverted, reversed image orientation.)
Coordinates are Epoch 2000.0. Objects are in order of their inclusion
in Ferguson's table in SKY & TELESCOPE. Data of the objects were provided
for publication here by permission of John Sanford from OBSERVING THE
CONSTELLATIONS, and by Dr. Jack Marling of Lumicon. Observers may
find more information, plus photos and both narrow and wide field
finder charts, by clicking on the appropriate "Deep Sky Browser" page,
linked to the website of Mikkel Steine:
www.messier45.com.
Click for our updated report on this object.
NGC-1514 (PK165-15.1) Mv=10.9. Taurus: 4h, 9.2m; +30° 47'.
A moderate-sized planetary somewhat over 2 arcminutes in diameter.
Ferguson finds it an 'excellent' object, even with a Questar in
Houston! In the Santa Cruz mountains with an 8" scope, it is very
easily seen around a 9th magnitude star: a faint, irregular disk at
magnifications of 80 to 200X with an oxygen-line filter. Detectable
without the filter, but much better with it! Heber Curtis drew it
in 1918, based on photographs he made with the Lick Crossley reflector:
the detail of Curtis' rendition was not evident with a mere 8" scope.
Observed in a sky bright with light pollution, but blessed with
excellent transparency and steady seeing. Worth the effort of
searching!
Click for Deep-Sky Browser Page
for NGC-1514.
NGC-2392 (PK197+17.1) Mv=9.2. Clown or Eskimo Nebula in Gemini:
7h 29.2; +20° 55'.
This object of more than 40" diameter is so well known that it does
not require an extensive description, other than to add that the uneven
halo around the bright center is easy to spot in a small telescope. In
an 8" scope, the outer shell does not break up into the bright clumps
seen in a large instrument, but rather has a faintly mottled, uneven
appearance. I observed it last in a broad patch of zodiacal light before
dawn that had 'wiped out' the faint stars of the region: yet, the planetary
was clear and bright.
Click for Deep-Sky Browser Page
for NGC-2392.
NGC-3242 (PK261+32.1) Mv=7.8. The "Ghost of Jupiter" Hydra:
10h, 24.8m; -18° 38'.
Though the famed early 19th-century observer Admiral Smyth found it
to be pale greyish-white in his 6" equatorial refractor, Webb and most
later authorities compare its hue to the pale blue of the planet Jupiter,
which it resembles in angular diameter. In my 8" scope it was clearly
tinted blue, like an otherworldly and ghostly rendition of our relatively
nearby Jovian neighbor. A filter is not an absolute necessity, as the
object readily will be apparent even in a moderately light-polluted sky.
Click for Deep-Sky Browser Page
for NGC-3242.
NGC-6210 (PK43+37.1) Mv=8.8. Hercules: 16h, 44.5m; +23° 49'.
A large planetary (uneven shape: possibly about half an arcminute
long by somewhere from 8-14 arcseconds in width), featuring surprisingly-
high surface brightness. Dr. Jack Marling calculates a modern visual
magnitude figure of 8.8; our Waldee-Wood EYEPIECE program then
determines from that measurement an approximate surface brightness
of almost 6th magnitude per square arcminute of area! I observed it
clearly [c.1995] when it was elevated only about 40 degrees above the
horizon in a sky with a naked-eye stellar magnitude limit of about 5.2.
At 50x, the shape was evident. With 200x, I suspected the presence of
an outer halo, which was -- amazingly -- perfectly evident with a 2.5mm
ocular, providing over 400x! Usually nebular objects disappear in an
8" scope with such high magnification: this object bears scrutiny!
Click for Deep-Sky Browser Page
for NGC-6210.
NGC-6445 (PK8+3.1) Mv=11.2. Sagittarius: 17h, 49.2m; -20° 1'
("Little Gem")
At first I was perplexed by Ferguson's article, for he describes this
fairly large (3' circular) planetary without a nickname in his list; yet
he ascribes the name "Little Gem" to NGC-6818, also in Sagittarius.
However, practically every OTHER reference I consulted calls NGC-6445
the "Little Gem" nebula. [On the web, "Little Gem" is used more often
for 6445 than for 6818. Roger Sinnott's NGC 2000.0 ascribes "Little Gem"
to 6445, and most other references that stem from this volume also concur.
According to the NGC/IC Project, NGC-6445 was discovered by William
Herschel in 1786, with the 18" speculum telescope.
I determined that NGC-6445 is rather hard to find in the fall, with
Sagittarius irrevocably sinking further below the western horizon, but
that it could be detected with some diligent searching. Even in the
rough seeing just 20° above the skyline, this small speck of bright light
stood out from the sharper stellar points in a crowded, milky field.
I identified it positively, using a general narrowband nebular filter at
80x: with an oxygen filter at 200x, the nebula was bright, while the
surrounding stars almost disappeared. Under these poor viewing
conditions, it appeared to be a bland, uniform disk.
Click for Deep-Sky Browser Page
for NGC-6445.
NGC-6543 (PK96+29.1) Mv=8.1. The Cat's Eye Nebula in Draco:
17h, 58.6m; +66° 38'.
Ferguson discerned surface irregularity with his tiny Questar
scope; in my 8" aperture richfield instrument, this medium-sized (20"+
diameter) planetary was a bright, fairly even oval disk, with almost no
variance in luminosity until scrutinized with a 2.5 mm EP providing over
400x. Thus, differences in telescope, exit pupil, sky condition, and
observer cause a divergence of opinions! The high surface brightness
requires only a moderately-dark sky for a good view: an oxygen filter
seemed merely to help darken the background. An excellent object that
unfortunately yields little of its wild shapes and gorgeous colors,
depicted in the fabulous Hubble image on the cover of the April 1995
SKY & TELESCOPE magazine.
Click for Deep-Sky Browser Page
for NGC-6543.
NGC-6629 (PK9-5.1) Mv=11.3. Sagittarius: 18h, 25.7m; -23° 12'.
This is strictly a summertime object! As first sought at the end of
August with the 'Teapot' dipping into the smoggy air just above the
horizon, it was not detected by me. Three days later I was lucky to catch
it around midnight, when only about 30° above the distant Santa Cruz
horizon. A nearly-round 16-arcsecond-diameter grayish or bluish disk,
the planetary seemed fuzzy and non-stellar at 200x. It was discernible
at only 50x: an oxygen-line filter darkened the background, and would help
to reveal it in a sky suffering from severe photon pollution. In my 5th-
magnitude naked-eye-limit sky, NGC-6629 was detectable without the filter.
Click for Deep-Sky Browser Page
for NGC-6629.
PK64+ 5.1; ARO 11 Mv=11.3. Campbell's Hydrogen Star, Cygnus:
19h, 34.8m; +30° 31'.
After an initially-frustrating exploration of the region of this
object, I did a bit of research, utilizing the documentation in the CD-ROMs
REDSHIFT and PROJECT PLUTO: GUIDE. Campbell's star is currently rated
at a visual magnitude of 9.02 according to the Hubble guidestar data-
base, in which is it listed as GSC 2655:4032; in the 19th-century Bonner
Durchmusterung (sky survey) it is BD +30°3639; the old (sometimes rather
inaccurate) Henry Draper catalog, it is HD 184738, which lists it as 10th
magnitude. The star at the center of the planetary is unusual: its
spectral rating is Ocp (very hot: greater than 25,000K, with a peculiar
spectrum displaying sharp lines.) The star will be easily seen in binocu-
lars or almost any scope; the surrounding gases of the planetary are said
to be extremely faint. Search almost 4 degrees west in right ascension
from M-56 in the constellation of Cygnus.
This faint object will not be plotted on all star atlases: it is
included on p. 118 of the Uranometria's Vol. 1 under the Perek & Kohoutek
number 64+ 5.1. This object is the one that should really nail Ferguson's
reputation as a splendidly-gifted observer! With his little 3.5" Questar,
he reported that the tiny nebular core was barely detectable, employing an
oxygen-line filter; yet it seemed brighter with a broadband LPR filter.
Setting circles could not offer the accuracy needed to locate the object,
so I prepared a chart with the GUIDE CD-ROM that showed a field of 15 arc-
minutes radius around the nebula. Only by means of the excellent upright,
correct-orientation finder that I use could I be sure that I was even near
the right area. After trying during several fall nights in the Santa Cruz
mountains in late summer of 1995, I almost concluded that I had seen the
pale, evanescent shell of gas that surrounds the star, following Ferguson's
lead by utilizing an oxygen-line filter. But on reconsidering my (inconclusive)
notes and drawing, I was not certain WHICH of the objects in the field was
the planetary. A telescope with a very high focal ratio and little light-
scattering, such as the Questar 3.5", may be better suited to achieve
extreme high contrast views than my 8" f5.2 Newtonian!
"I was perplexed by the data on Campbell's Star," wrote Dr. Jack
Marling after reading my notes, recording Ferguson's positive observations
and my more tentative ones. "This [object] was always best seen by an H-
BETA [tm] filter, and was essentially invisible with an O-III filter,"
added Dr. Marling, who reported that with a 17.5" f/4.5 scope, the
planetary around Campbell's star was a compact shell surrounding a bright
star, which was resolved into a disc with the H-BETA filter, employing an
eyepiece providing about a 4.5 mm exit pupil for a magnification of 105x.
Slightly later than a year after my initial attempts to view the
nebula, I finally verified it using an associate's 17.5" Dobsonian
scope and the hydrogen-ß filter. Two months later, I was able to confirm
the sighting, using a mere 6" aperture f5 scope in a sky with about 6th-
magnitude naked-eye stellar limit, with the object near the zenith. With
an eyepiece field of 31' using a 4.8 mm ocular, 159x magnification, and
the filter, the star had a slightly fuzzy appearance, and was not
appreciably dim when compared to the image without the filter. The star
was obviously fuzzy when viewed with a 2.5 mm eyepiece at 305x. Using
the oxygen-line nebular filter with either eyepiece caused an almost
complete extinction of the image.
Owners of the H-BETA filter, which was primarily intended for viewing
faint H-II regions or large, low-surface brightness hydrogen nebulae (like
IC-434, the glowing region beyond the dark Horsehead cloud B-33), will be
delighted to discover another use for this filter.
Click for Deep-Sky Browser Page
for PK64+ 5.1.
NGC-6818 (PK25-17.1) Mv=9.3. ANOTHER "Little Gem" Nebula, in
Sagittarius: 19h, 44m; -14° 9'.
Frankly, I revelled in getting a view of nearby faint and elusive
Barnard's galaxy (NGC-6822) even more than I enjoyed seeing this medium-
sized (20"+) annulus. I agreed with Ferguson that the central region of
this planetary seemed darker than the outer envelope. In a sky with a
'seeing rating' of 7 - 8 (extremely calm), despite a little light pollu-
tion, this "little gem" had sufficient detail and contrast to be noted
as being distinctly sharper and more defined on the NW side. Another
very apt description, confirmed by this observer, was the entry in the
Skiff & Luginbuhl "Observing Handbook and Catalogue of Deep-Sky Objects".
This item definitely does NOT require a gigantic telescope in order to
make meaningful observations of its nature!
Click for Deep-Sky Browser Page
for NGC-6818.
IC-4997 (PK58-10.1) Mv=11.3. Sagitta: 20h, 20.2m; +16°, 45'.
This tiny (2") slightly oval planetary is almost stellar at low
powers; it is revealed as a near-disk at 200x to 400x in my 8" aperture
scope. It was not too difficult to verify once the proper eyepiece field
was found. In a heavily light-polluted environment, I am sure an oxygen-
nebula filter will make a great difference in being able to discern this
object as distinct from the field stars: in a sky with a naked-eye
stellar magnitude limit of about 5.5, the filter was not absolutely
necessary to confirm the object, though it did assist.
Click for Deep-Sky Browser Page
for IC-4997.
Click for our updated report on this object.
NGC-7008 (PK93+5.2) Mv=10.7. Cygnus: 21h, 0.6m; +54° 33'.
I don't recall looking at this marvelous object before a late-summer
1995 observing session with a professional companion, who was studying
the composition of planetaries as part of his astronomical work.
If this object had been given a nickname with which to attract the
fancy of amateur astronomers, it would be a sure-fire favorite!
For this wonderful planetary has a remarkable variety of stellar and
nebular features, and -- like M-17 -- looks good with just about any
aperture amateur scope! In my associate's 17.5" Dobsonian, an
asterism of finely-scattered stars, sporting a fine 18" double, opens
into a fan-shaped spray of nebulosity that is dramatically bright
and well-defined. Despite its length of nearly 100 arcseconds,
the surface brightness is high, so the nebula is easily visible in a
3-5 inch aperture scope. Less dramatic in my 8" than in the large
Dobsonian, NGC-7008 is nevertheless one of the few deep-sky objects whose
eyepiece-views really resemble photographs. Much detail was evident at
high magnification, using 200x and an oxygen-nebula filter. Don't miss
this one!
Click for Deep-Sky Browser Page
for NGC-7008.
NGC-7009 (PK37-34.1) Mv=8. "Saturn" Nebula in Aquarius:
21h, 4.2m; -11° 22'.
Yep, looks rather like Saturn if you use a little imagination. I
have looked at this object so many times in the past 15 years that I did
not make a special try while going through the Ferguson list. Yet, just
after Thanksgiving in 1995, I did briefly spy it while searching for other
objects in the constellation. The "ansae" which have little jiggly ends
when viewed in a deep photographic exposure are just at the 'imagination'
level in my 8" scope view; yet I have seen them clearly with a 17.5" Dob-
sonian. Well worth snaring if you are not tired of the object, for it
does offer interesting structural detail. With the oxygen-nebular-line
filter I would guess that it would be visible right in the middle of the
Santa Clara valley: it is BRIGHT!
Click for Deep-Sky Browser Page
for NGC-7009.
Click for our updated report on this object.
NGC-7026 (PK89+0.1) Mv=10.9. Cygnus: 21h, 6.3m; +47° 51'.
A most interesting object, also studied by Curtis, whose drawing
after a photograph is included on p. 20 of Lawrence Aller's monograph on
planetary nebulae, issued in 1971 by Sky Publishing. I did not find that
it looked at all like the drawing, since I was using a mere 8" scope in
indifferent skies that suffered from some streetlight pollution. Yet,
my notes recorded the comment "VERY INTERESTING LOOKING!", capitalized
to indicate my strong impression. The bi-nuclear detail (noted by
Skiff & Luginbuhl) was observed at 422x, using a 2.5 mm eyepiece. The
27x11 arcsecond diameter nebula was discernible as a planetary with
only 50x if an oxygen-line nebular filter was employed: a dark lane was
just barely visible with 200x and the filter.
Click for Deep-Sky Browser Page
for NGC-7026.
IC-5217 (PK100-5.1) Mv=11.3. Lacerta: 22h, 23.9m; +50° 58'.
Since this object was not included in Luginbuhl & Skiff's handbook
mentioned above, I was worried that it might not be easy to spot, despite
the inclusion in Ferguson's table of objects found with his Questar. Yet
Ferguson apparently noted its high surface brightness, since it was
visible to him despite its 6" diameter. I found it indeed hard to locate.
It was stellar-appearing at low powers; the oxygen-nebula filter helped
isolate it in the starry field. Without the filter, it seemed to have
about the same luminance as most of the stars nearby. Tenacity and
patience -- and the oxygen-line filter -- are called for in locating this
challenging object.
Click for Deep-Sky Browser Page
for NGC-5217.
Click for our updated report on this object.
NGC-7293 (PK36-57.1) Mv=7.3. "Helix" Nebula in Aquarius:
22h, 29.6m; -20° 48'.
I skipped this huge (12 arcminute diameter) object during my overview
of Ferguson's planetaries, since I had made a careful study the previous
year, while examining objects in order to create "eyepiece view" images
for our Waldee-Wood program EYEPIECE. If I may quote myself in the file I
wrote for the program:
The "Helix" looks different from typical planetary nebulae like
the round and fairly even M-97 or NGC-7662. [John] Sanford [in
"OBSERVING THE CONSTELLATIONS": quoted by permission] notes that the
broken filamentary structure indicates a rapid movement of expanding
gas. Deep photos reveal a faint irregular disk with striations leading
outward from the center...to get a clear eyepiece view: (1) use a very
wide-field scope at the lowest magnification; (2) view when the 'Helix'
is nearest the meridian... (3) use a dark sky site; and (4) be sure to
employ a nebular filter."
I am positively shocked and amazed that Ferguson could detect this
object with such a low surface brightness using a 3.5" Questar in the
light-polluted sky of Houston. Surely only the oxygen-nebula filter
permitted this observation to be made: in the Santa Cruz mountains, I have
often found the "Helix" to be nearly invisible without the filter, using
an 8" aperture scope. Only in a very dark-sky site does this object
clearly show up without a contrast-enhancing filter as a broken smoky oval:
in such a sky, adding the filter permits examination of the actual
apparently-helical coils of nebulosity.
Click for Deep-Sky Browser Page
for NGC-7293.
NGC-7662 (PK106-17.1) Mv=8.3. "Blue Snowball" in Andromeda:
23h 25.9'; +42° 33'.
After straining to see any trace of color while viewing the above
planetaries, it is a pleasure to end with the snowball: it is REALLY BLUE,
even in an 8" aperture scope. In a 17.5" instrument, it shines as a
veritable beacon in the sky! Though relatively large for a compact
planetary of its type (32 arcseconds in diameter), NGC-7662 has a very
high surface brightness. My pencil-drawing -- hard to reproduce through a
scanner -- shows a nice oval smudge growing much denser toward the middle
at 400x. Dreyer gave it a "!!" designation in the 1888 NGC: one notch
below the "!!!" for M-42. I agree.
Click for Deep-Sky Browser Page
for NGC-7662.
SELECTED REFERENCES
Articles and Books:
Data Drawn from OBSERVING THE CONSTELLATIONS by John Sanford, 1989,
Fireside/Simon & Schuster, and quoted by permission.
PLANETARY NEBULAE FROM THE CITY by Donald R. Ferguson, 3615 Ledgestone
Drive, Houston TX, 77059, from OBSERVER'S PAGE (edited by Dennis Di Cicco),
SKY & TELESCOPE, April, 1995.
NGC 2000.0, edited by Roger Sinott: 1988, Sky Publishing.
OBSERVING HANDBOOK AND CATALOGUE OF DEEP-SKY OBJECTS by Christian B.
Luginbuhl and Brian Skiff; 1989, Cambridge University Press.
URANOMETRIA 2000.0 by Tirion, Rappaport, Lovi; 1987-89, Willman-Bell.
THE BEDFORD CATALOGUE by Admiral William H. Smith; 1844; reprinted 1986,
Willman-Bell.
CELESTIAL OBJECTS FOR COMMON TELESCOPES, Vol. II, by Rev. T. W. Webb;
1859; reprinted 1917 and 1962, Dover Publications.
PLANETARY NEBULAE by Lawrence H. Aller; 1971, Sky Publishing.
VIEWING PLANETARY NEBULAE (Summer Constellations) by Dr. Jack
Marling, Summer 1986, DEEP-SKY Magazine, Kalmback Publishing.
Software:
REDSHIFT CD-ROM for Windows or Mac: Maris Multimedia, 3871 Piedmont
Avenue, Oakland, CA. 94611
GUIDE 4.0 (CD-ROM for DOS): Project Pluto, Ridge Road, Box 1607,
Bowdoinham, ME. 04008
Equipment:
O-III (tm) Filter; H-BETA (tm) Filter:
Lumicon Company
Data:
Visual Magnitude Data (Mv) by Dr. Jack Marling, Ph.D., included by
permission.
Other object data courtesy of John Sanford, from OBSERVING THE CONSTELLA-
TIONS, Fireside/Simon & Schuster, quoted by permission.
Images:
Most of the thumbnail images above were prepared by the author using
the Palomar Observatory Sky Survey I plates, obtained from the Digital
Sky Survey, available on the web:
http://archive.stsci.edu/cgi-bin/dss_form
Acknowledgments are required for use of the images, and may be found at:
http://archive.stsci.edu/dss/acknowledging.html
Other images were prepared from material in the Waldee-Wood Astronomical
Software program EYEPIECE, including the picture of NGC-7293, courtesy of
Chuck Vaughn. Several of the planetary nebula images were modified by
the author to improve their resemblance to eye views through telescopes,
such as NGC-6543, NGC-7009, and NGC-7026. Also please note that the nebulae
are not shown in proper proportional relationship, since some are very small
with details that are hard to discern (and had to be blown up in size) and
others, such as the "Helix" nebula, are extremely large and had to be
diminished to fit the thumbnail pictures.
Link:
Deep-Sky Browser Pages: www.messier45.com
Questar (tm) is (c) Questar Corporation, New Hope, PA. Lumicon, O-III,
H-BETA (tm) are (c) Lumicon Company. All other trademarks are copyright
(c) their original copyright holders. This article Copyright (c) 1996-2006,
Stephen R. Waldee. All Rights Reserved.
