Object of the Week July 2, 2017 – NGC 6369 Little Ghost Nebula

Object of the Week July 2, 2017 – NGC 6369 Little Ghost Nebula

NGC 6369, Henize 2-232, Sanduleak 2-207, Wray 16-277, PK 2+5.1, PNG 2.4+5.8

Type: Planetary Nebula
Constellation: Ophiuchus
RA: 17h 29m 20.7s
DEC: -23° 45’ 35”
Magnitude: 11.4
Size: 58” x 34”
Magnitude (central star): 15.9


NGC 6369 is a small - about half the apparent diameter of Jupiter - but relatively bright – magnitude 11.4 - planetary nebula located in the constellation Ophiuchus. At a declination of -23° July is the prime time to catch it as it culminates - here at 41°N that means it doesn’t quite get to an altitude of 30°. However, don’t let that stop you because NGC 6369 is well worth a visit.

NGC 6369 was discovered by William Herschel on May 21, 1784. His discovery notation for H IV-11 reads: “pretty bright, round, pretty well defined planetary disk, 30” to 40” in diameter.” Some sixty-three years later in 1847 his son, John Herschel, observed NGC 6369 from the Cape Town, South Africa and noted his observation: “annular nebula. Exactly round, pF, 12 arcseconds diameter, well-terminated, but a very little cottony at the edge, and with a decided darkness in the middle, = star 10m at the most. Few stars in the field, a beautiful specimen of the planetary annular class of nebulae.”

This object is known to amateur astronomers as the "Little Ghost Nebula," because it appears as a small, ghostly cloud surrounding the faint, dying central star. It is a double-shell planetary nebula with a filamentary outer shell or envelope and faint bipolar extensions.

The Little Ghost Nebula is about 4° northeast of Theta Ophiuchi. You might expect it would be difficult to track this small planetary nebula down – but not so much. It lies within Barnard’s dark cloud B77, just north of the Pipe Nebula B78. Being in this sparse field helps facilitate its identification against the blackness of B77.

Attachment 2601
finder chart

Attachment 2600
The Little Ghost Nebula floating in the blackness of Barnard's dark cloud B77

The planetary nebula is readily detectable in scopes as small as 4 inches where it appears as a nearly perfect sphere. Increasing aperture and magnification will begin to yield more of the complex details hidden in this planetary nebula.

The following collection of observation notes will provide you guidance on items to note and consider when you observe the Little Ghost Nebula.

“A regular, nearly round ring...quite faint" says Curtis, “NGC 6369's faintness is no surprise, as the planetary nebula, in far southeastern Ophiuchus (two degrees northeast of Theta Oph) is only 7 degrees west of the center of the Galaxy (and of the Summer Solstice in Sagittarius), and is thus very much dimmed by intervening interstellar dust.” (H. D. Curtis in the Publications of the Lick Observatory, Volume 13, Part III, 1918)

Attachment 2603
H.D.Curtis sketch, Lick Observatory, 1918

"[I] was surprised to find it easily. The greenish tinge characteristic of planetaries was obvious, and the seemingly star-like object looked brighter than listed.” (Walter Scott Houston)

“Annulus is clearly visible in a 6-inch.” (Luginbuhl and Skiff)

“What I found remarkable is that Herschel failed to notice the object’s annularity, which is a perfect smoke ring…the nebula’s dim and imperceptible outer envelope (at least in small scopes) doubles the object’s size.” (O’Meara)

“…it appears like a translucent spirit materializing in the darkness. It appears very stellar at low power but swells with averted vision. With any moderate magnification, the nebula is a perfect opal – smooth, round, and, well, opalescent. At 303x (under good seeing), the ring has a sharp interior that gradually dims outward. The central star, which shines at 16th magnitude, cannot be seen.” (O’Meara)

In a 10-inch reflector at 87x “round, green, and with the edge quite sharp” and at 137x “easily make out the nebula’s dark center.” (R. Morales)

“A pretty planetary nebula, also discovered by William Herschel. Look for the mag 15.9 central star in this planetary nebula.” (Jane Houston Jones)

Attachment 2602
(c)Adam Block, Mt Lemmon Observatory, showing complex detail and the faint outer lobes

Now it’s your turn…
Give it a go and let us know!

I really need to look at this one again, now that I have better skies. My notes from my only observation (12.5" f/5 Dob; 14mm ES eyepiece [112x, 42' TFOV]):

7/4/14-7/5/14

CRAB ORCHARD WILDLIFE VIEWING LOOP
MOON: 7 days, still present at beginning
SEEING: 6
TRANSPARENCY: 4-6
NELM: 5.3; faint MW, not much detail in Rift, not much definition over by M7
WEATHER CONDITIONS: v. damp (humid); ground fog as departing

with LW and his friends (Jeff & Tammy??)

11:12
NGC 6369 (Oph) Little Ghost—v bright planetary, no filter, swept up super easily—about half an arcminute maj axis—seems to be annular— no central star—bright ring with tiny bit of fringe halo—slightly oblong in P-F direction—forms tip of almost equal triangle with 10th/11th stars—seeing not good enough for higher power

This one should be a favorite--it's a great little nebula!

Hi Mark,
I've observed the PN several years ago with a 12" newtonian at 208x magnification with [OIII]-filter. Here is my sketch:
Attachment 2604

Thanks Mark, this is a great object, and in reviewing my notes I've discovered that I haven't observed it with my 28 inch yet! So here's a screen shot of my notes made with my 20 inch f/5 scope from about 15 years ago.

Attachment 2605

Now I need to get out there and make a proper sketch with the 28.

I've observed NGC 6369 numerous times, but haven't taken any notes in the past 10 years. These are my last two logged observations with my 18". No mention of the central star.

18" (7/14/07): striking view of this annular planetary at 280x. The 30" halo is punctured by a relatively large ~18" hole. The rim is noticeably uneven in surface brightness with a brighter arc along the northern side. Spectacular at 700x and the brighter northern rim has a couple of very small brighter spots.

18" (7/22/06): beautiful view at 435x. The 30" annular ring is brightest along a "C" shaped section from NE moving clockwise to the SW and locally brighter at the NW end. The central hole is round, well-defined and relatively large compared to the rim.

Regarding Stephen O'Meara's comment "What I found remarkable is that Herschel failed to notice the object’s annularity, which is a perfect smoke ring…the nebula’s dim and imperceptible outer envelope (at least in small scopes) doubles the object’s size."

I checked William Herschel's discovery on 21 May 1784 (sweep 222), where he describes the planetary as "a curious round, tolerably defined pB nebula 30 or 40" in diameter." The observation was made in the late morning, nearly 15 minutes AFTER he logged the comment "Daylight very bright". Herschel often started observing in twilight and ended during morning twilight, so perhaps it's not so remarkable he didn't notice the annularity.

Nice object through very low in the sky for middle of Europe. Low filter effect, best view without filter. Ring not exactly round with some structure. Faint extension to the W suspected. Even with high magnification (16-inch) central star not visible.

16", 360x, no filter, NELM 6m5+, Seeing II
Attachment 2606