Deep sky observing report, Mount Ceder - 2008 Dec 22

posted: 3091 days ago, on Monday, 2009 Jan 05 at 06:03
tags: astronomy, deep sky, observing report.

Mount Ceder is a farm in the southern reaches of the Cederberg Conservancy (32:38:58S, 19:24:31E) on which several four-star guest cottages have been built. I was invited by Dieter and Hilda Willasch to spend two evenings (2008 December 22/23) with them at Mount Ceder for some star gazing.

Dieter, an accomplished astrophotographer, took along some of his gear (including an 80mm APO and a Takahashi equatorial head), and I took Maphefo (an 8-inch Dobsonian).

After an early supper we set up on the lawn of the remote cottage and sat back to watch nightfall, one of Nature's understated spectacles. The sky was beautifully dark; sigma Octantis was no challenge, and my limiting magnitude was around 6.3 (based on a star count within the False Cross).

Maphefo showed the Keyhole in the eta Carinae nebula to be rich in detail, and the Orion Nebula showed equally delicate structure.

Walking to the side of the house, facing north, and Pegasus is seen vaulting over the distant mountains. Messier 31, the Andromeda Galaxy, is a naked-eye smudge low above the mountains, this despite the fact that I'm not properly dark adapted. Through Dieter's 16x70 Fujinons, the galaxy appears to stretch across the full four-degree field of view.

And Messier 33, the Triangulum Galaxy, looks like it could be a naked-eye object (but isn't). Yet the view through binoculars is incredible it looks a bit like Omega Centauri! (In 1997, observing from within the Jonkershoek conservation area, I noted it resembled a "large a-nuclear globular cluster".)

Flushed with excitement, I decide to surprise Dieter and show him the Horsehead. Turning Maphefo onto zeta Orionis as the starting point of the starhop immediately shows NGC 2024 as a large bifurcated nebula east of the Belt Star. As is often the case, I see these types of objects as dark shapes surrounded by bright patches. William Herschel, for example, recorded it as a "wonderful black space included in remarkable milky nebulosity". Others see it as a bright nebula; Bailey, for example, called it a "nebula; 2 distinct, irregular patches, each 10' x 15' long." Horses for courses, I can't help thinking (with apologies to Barnard 33).

I'm impressed with how easy NGC 2024 is no real dark adaption yet, the background sky rather bright and contrast not particularly high (the Coal Sack is not punchy, and the Dark Doodad is rather dim).

Nearby NGC 2023 is a pretty small, distinct glow with its somewhat off centre 9th magnitude star.

But massive IC 434 is not apparent; maybe in the vicinity of zeta Ori, but hardly elsewhere. The uncomfortable position of the Dobsonian's eyepiece too high to sit, too low to stand makes prolonged high-magnification viewing impossible, and despite the Horsehead's position being dead-centre, it eludes me. Tomorrow night.

On the Carina-Vela border lies the moderately large & faint cluster IC 2488, its 20 or so stars making an obvious grouping at 48x (25mm). Its brighter members are clearly arranged in two parallel arcs, and there are more stars on offer. Third-magnitude N Carinae to the east acts like a beacon to draw attention to the cluster, which is a delight to sketch and study at higher powers.

Two degrees north lies kappa Velorum, and midway between N and kappa is the planetary nebula NGC 2899. At 48x and 96x the nebula is readily visible, appearing as a pretty faint, pretty large, irregularly round glow. The delicate nebula is noticeably bounded by four 12th magnitude stars, as if they are staking it out and have pinned it down. Ten arcminutes north-northwest of the nebula lie two 8th magnitude stars (SAO 236986 and SAO 236985) the nebula appears slightly larger than the separation between these two, so I'd peg it at 1.5-arcminutes in diameter.

As is often the case with objects that have detail that is at the limit of one's ability to see (or at least, at my limit, and particularly with round-ish objects), the initial impression of a round shape becomes less certain. I start "sensing" all sorts of slightly elliptical shapes instead, but the orientation refuses to remain constant. So with NGC 2899 in the 8-inch tonight I eventually cautiously settled for an ever so slightly elongated outline, oriented roughly north-south.

Later, looking at some of Dieter's spectacular astrophotos, he shows me examples of his favourite objects: the open clusters. He pauses at NGC 3766, "This is Hilda's Cluster," he grins. This beautiful grouping is embedded in the rich Milky Way, and bears a striking resemblance to the Jewel Box; in March 1997, observing from Jonkershoek, I noted it as a "triangular cluster appearing like a lop-sided Jewel Box". Both clusters feature a prominent stellar triangle, with a host of smaller stars scattered to one side. Dieter notes, however, that NGC 3766 is much richer in stars, so we decided that it should be called the Rich Man's Jewel Box.

Other proper names were soon discussed. The first was the awesome NGC 3532. Dieter calls it the Fish Cluster, placing 5th magnitude X Carinae as the eye of the creature. Not convinced, I take a look at it through his 80mm APO. With the fish bias in mind, I also see one, but trace it differently, with X Carinae not a part of the fish, but looking rather like a lure cast by a celestial angler. Dieter also noted that the stars can also be seen as the outline of Horus, the Egyptian god. However, the piscine precedent was set in my mind.

With interest I later noted that in all the collected observations I have of this cluster, even the most florid authors have avoided the "looks like a" game. The only exception is Bostonian Todd Gross (IAAC, 1998), who wrote that the "cluster roughly resembled the constellation Leo." Now that's something to check up on next time.

In the case of NGC 3114, however, things are much different, and many observers have had a go at "looks like a". The first indication that something is special about the stellar arrangement in this cluster is given by James Dunlop, who in the 1820s noted that its stars are "arranged in curvilinear lines intersecting each other."

Glen Cozens calls it "a snail's shape" and Magda Streicher says that "the appearance of a butterfly is called to mind". I first saw the cluster in 1980 with a 2-inch refractor and noted six bright curves of stars giving it the appearance of a spiral galaxy. Later, I likened it to an octopus.

Dieter's description of NGC 3114 as the Hand Cluster certainly deserves a high-five the curves of stars do indeed look like an X-ray of a hand. Check it out yourself and see what you think it looks like.

I never did get to look for the Horsehead the next evening (although we did see horses at breakfast) because the sky uncharacteristically clouded over. Yet of all the things I saw at Mount Ceder, that evening's partially cloudy night sky was surely the most impressive. The inky-black silhouette of the surrounding mountains gave way to vast, almost-black expanses of clouds, reaching from horizon to horizon and moving slowly, with vast tracts of open sky in-between. To the south, high up, the Magellanic Clouds were two small incongruous light-grey patches. And between the clouds, their edges dissolving almost imperceptibly into the background, shone the brilliant myriads of stars. This must be what it looks like to live on a planet orbiting a star embedded in a vast complex of dark nebulae. And dark nebulae, after all, are my passion.

Slide show

 Our cottage at Mount Ceder.  [click to start slide show]

nothing more to see. please move along.