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

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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.

NGC_6369_map.jpg
finder chart

n6369dss.jpg
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)

n6369Curtis_sketch.jpg
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)

NGC6369_Planetary_Nebula_from_the_Mount_Lemmon_SkyCenter_Schulman_Telescope_courtesy_Adam_Block.jpg
(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!