(This article originally appeared in the Q2 2000 STAR news letter. -Ian)

Indulgence In Obscurity Part III – The Summer Planetaries
by Eric Honeycutt

Ever since last October, I have been waiting in earnest for the Summer Milky Way to present itself in an early enough hour to spend appreciable time hunting down the many wonderful and obscure objects that lie behind its structured and highly detailed, star-strewn belt. Now, of course this isn’t to rule out the many wonderful objects that correspond to the other seasons – not at all! It’s just that there is so much to observe in the Summer sky that it seems that I never even have enough time to revisit the once-observed objects, much less the many new and intriguing ones. I do want to establish a criteria for this article however. That criteria is very dark skies. Here in Raleigh area, the summertime is the worst for observing deep sky objects. Mainly because of the haze that tends to always turn a once-blue sky into a milky-white veil of transparent muck. For planets, this works out pretty good because haze usually results in steady skies – a real rarity for this area! However, there are many great dark sky locations within a three or four hour drive that will usually negate the hazy aspects of summertime. Thus, I encourage everyone who reads this to seek out the dark skies of the North Carolina mountains or better still, the darker Highlands area of Southwest Virginia. Many times, you will get above the haze layer. Also, the humidity is lower and the nights are much more comfortable and quite transparent. Though the objects that I will present below will be able to be observed form our Big Woods site, true appreciation for these fine gems shall only be realized when a transparent night envelops you.

There are some really fine objects that cover the entire spectrum of deep sky targets that grace the summer sky. However, I am going to take this opportunity to highlight my favorite type of deep sky object (“dso” for short): PLANETARY NEBULAE! I love these stellar tombs so much that many times I will go out and observe nothing but these diverse dsos for the entire lunar absence. Their size, shape, variety, and dynamics always compel me to make them a top priority on my observing list. Therefore, I am going to offer a detailed array of the many fine Planetaries that are tucked away behind the familiar constellations of the Summer sky. Another reason is to try to get you really hooked on these little buggers (sometimes big buggers) so I can stop boring some of my RAC colleagues with my incessant rambling about them.

First stop: Scorpius. There are many great planetaries (“Pn” for short) in the Scorpion that warrant recognition. This region of the sky is home to an interesting catalogue of Pn known a the “Wray Catalogue”, among others. As a point of interest, the majority of Wray Planetaries have actually been found to be questionable in nature. They were mostly discovered and/or rediscovered back in 1966 while James D. Wray was working on his PhD thesis concerning the compilation of a catalogue of H-alpha emitting objects of the southern hemisphere. He used the objective prism spectroscopic survey plates taken by Karl Henize, which primarily picked up a ton of H-alpha emitting early-type stars. This is the reason that the majority of Henize and Wray designated Pns are quite small in angular size (typically <30"). It seems that if an H-alpha emitting object picked up on the plates had any other odd emission features that were not known to emission-line stars of that time, they were automatically assumed to be Planetary Nebulae. Of course, the number of varying types of emission line stars and symbiotic systems has grown so much since then that the majority of these previously misclassified Pns have been debunked. There are many good Wray-designated targets out there however that are true Planetaries. Wray 16-314 is a Pn that should be visible under dark skies with a low southerly horizon. Its declination lies at -39 so you must go low for it. However, a 10″ scope and the all powerful O-III filter should reveal a 13.8 (P) mag disk at 8.6″ in diameter. I did not glimpse detail (possibly because I was looking through so much air since the scope was lower than horizontal) but I did “blink” the Pn into confirmation. Remember, photographic magnitudes of Pn are not to deter an attempt at observation. Usually the visual magnitude will be one to even two magnitudes brighter. Also, an observation of an object that has only recently been catalogued is a treat. The added benefit is to also have in your notes, a record of objects that many amateurs have never even heard of, much less observed. It does do something for the morale of someone who may be experiencing astronomical burn-out that I have talked about in an earlier article. Anyhow, the coordinates of Wray 16-314 are: 17h 50m 44.3″ and -39° 17′ 24″.

Another Wray-designated object also happens to be a relatively well known NGC object. Wray 16-259 (aka: NGC 6302) is also known as the “Bug Nebula because of its strange, unusual appearance that resembles a beetle or a butterfly (whichever “ink blot” you prefer). High power and an O-III should be used to observe this one. It is roughly 45″ in length and has a very bright center that should not be mistaken for a central star (CS magnitude is at an impossible 21.1v). The bright central core is flanked by two extensions that form a horizontal hourglass shape. This one is easily visible in an 8″ scope with an O-III. It lies halfway between Shaula (the inner-most stinger star) and Mu Scorpii at: 16h 51′ 52.24″ and -38° 02′ 50.6″. Another great Wray Pn that also is a NGC object is:

Wray16-267 or NGC 6337. This has also been dubbed “The Cheerio Nebula” because of its obvious ring structure in photographs. This one is visible in an 8″ scope as a relatively bright disk with a seemingly darker center. Dark skies, medium to high power, and an O-III filter should reveal the annular structure with close scrutinizing and averted vision. It is 49″ in diameter and has a photographic magnitude of 11.9(P). A magnitude 12 star is superimposed on the NE side. Larger instruments easily reveal the central hole at high power. You will find this one at: 17h 22′ 15.6″ and -38° 29′ 01″.

The last Wray Pn that I want to address is Wray 15-1607 and also has an IC designation (IC 4637). This Pn is at a respectable 13.6 photographic magnitude and is 18.5 in size. High power and an O-III reveal an oblong or oval disk with relatively even brightness. A pretty starfield compliments this Pn. This Pn also has a very bright CS at 12.5. Coordinates are: 17h 05′ 10.4″ and -40° 53′ 07″.

Now on to Sagittarius we go for a really nice Pn by the name of “The Little Gem”.

NGC 6445 is named this because of its nice green color, especially when viewed with an O-III filter. Its photographic magnitude is at 13.2 and it has a size of 33″. In an 8″, the Pn is roughly as bright as the nearby globular cluster NGC 6440 which lies 20+ minutes to the south. Medium to high power should begin to reveal a central hole that is not truly round. Higher apertures show this object to be elongated. At 508x in my 22″, the Pn’s shape takes on the shape of a box with an elongated central hole. No CS is visible as it shines at 19.0 visual magnitude. This one can be found at: 17h 49′ 15.1″ and -20° 00′ 34″. Another worthy Pn in Sagittarius is NGC 6818 and it has an appropriate name of “The Little Gem” because it is similar to the Pn listed above, just smaller. This planetary is 48.0″ and shines at a bright 9.9 photographic magnitude. An 8″ scope will reveal a bright bluish disk that is nearly the same color as the Blue Snowball (NGC 7662) in Pegasus or The Saturn Nebula (NGC 7009) in Aquarius. You will only observe a disk about 20″ in diameter. See if you can discern the slight darkening contrast in the central region that is the central hole. A 12+ mag star lies just to the NW and SW. You will not see the 16.9 CS. In larger apertures a faint outer halo can be seen which justifies the larger 48″ diameter. In my 22″, the Pn appeared greenish and very bright as well as concentric in relation to the central hole which appeared round but small. It reminded me of a bagel that had been stepped on and flattened. The coordinates for this object is: 19h 43′ and 57.8″ and -14° 09′ 11″.

A quick stop in Ophiuchus will lead us to a really interesting bipolar nebula known as Minkowski’s Butterfly. Minkowski 2-9 is a superb object that requires high power to observe best. If the seeing will allow, try to use powers of 300x or more. The Pn is 30″ x 60″ and has a magnitude of 13.2. The CS shines at 15.6 but is visually much brighter. It can be seen in a 12″ at high powers. On each side of the Pn are two flattened extensions with greater brightness toward the CS, and fading as they extend. A separation between the CS and the two extensions are evident in larger scopes. This one is well worth finding for the advancing amateur.

Lets go to Scutum now for a very large and very overlooked Pn. This one is designated as IC 1295. I strongly recommend an O-III for this one because of its large size (90″) and its subsequent low surface brightness but it definitely responds well to the O-III. Once you observe this one, you might be surprised that you have never heard of this one before as I was (that is, unless you have heard of this one before…). This great object lies very close to globular cluster NGC 6712. An 8″ will reveal a large, circular haze that is grey in color. Two faint stars can be detected on the SW edge of the object. In larger instruments, and medium to medium-high powers reveal a distinct “owl-eye” pattern within the diffuse disk. It is very impressive in apertures of 12″ and larger. CS is visible at 15.5 if your scope can accommodate that magnitude, just remove the O-III filter first! Coordinates for this showpiece are: 18h 54′ 37.0″ and -08° 49′ 37″.

A constellation that has a plethora of Pns lies just above Scutum. It is the constellation of Aquila. There are many really great planetaries here that could make for an entire article in itself. However, since I am limited to article-length instead of thesis length (despite what my editor says), I will just pick out a few that really are stand-outs. The first one is NGC 6751. This neat little Pn has a distinct annular structure that surrounds a 15.4 mag Central Star. However, the CS apparently is a wide ranging variable as it has been glimpsed in 8″ apertures and it certainly was not 15.4 mag in my 22″. The ring structure does need a transparent yet steady sky (an oxymoron here, I know) but it is possible. The color is green. What is so neat about this Pn is that there is a fantastic red variable (V Aquilae) that lies to the NW just under 2′ away. This is a very red star that is quite impressive for the observer who doesn’t expect it to be in the starfield. Do not forget to check it out if you have not ever observed this one. I know that many from the RAC have observed it in the 22″ and were taken back with the intense red color. The coordinates for NGC 6751 are: 19h 05′ 55.5″ and -05° 59′ 32″.

Now get ready for a favorite NGC Pn of mine. This one is NGC 6781. This Pn is a beautiful and very large 1.8′ disk. The starfield is rich and the Pn really stands out with an O-III. It seems to be missing a “bite” that has been taken out of its northern edge and has a central darkening that is apparent with averted vision in a dark sky. In larger apertures the central darkening is readily apparent and even gives the impression of a hole that is not truly round. If you have never observed this one before, do not pass it up! Coordinates are: 19h 18′ and +6°33′.

Onto a really cool Pn now that is far underrated in my opinion. NGC 6804 is a nice, 35″ disk that stands at 12.2 (P). If your seeing allows, try to use powers of 250x to 300x. With this power, don’t use an O-III. In my experience, you will see more detail. If you can’t get above 200x, use the O-III. At first, you will probably only see a disk. But higher powers and concentration will begin to show a conspicuous oblong or football shape, central hole. It reminds me of NGC 3242 “The Ghost of Jupiter” though not as pronounced. See if you can spot the 14th+ mag CS. If so, try to spot the 2 faint stars that are placed on either side of the CS. If that is obtainable, you are looking at a real treat: a bright disk, an inner, elliptical envelope, that has a chain of 3 stars that run right through the center of the planetary. In larger instruments, you will see this much easier and it is a great sight! Coordinates are: 19h 32′ and +9°13′.

Lets go to another area of the sky that is well known for its abundance of Planetary Nebula. This is the Cygnus region. There are many diverse Pns here that can show a wealth of appreciable detail under the right conditions and experience level. But first let us analyze a really neat object known as “Cambell’s Hydrogen Star”. The designation is PK64+5.1. Its visual magnitude is 11.3 and has a small diameter of 7.5″. It is a “Class 4″ Pn that has a very bright and distinct orange CS that shines at mag 12.5. The bright star makes it difficult to observe the faint outer disk but it is discernible. I have found that an O-III does not help a whole lot on this one but maybe it was the orange-red star that keeps distracting me. Use the highest usable power to see the circular haze around this unusual object. The Pn is also designated Henize 2-438. Coordinates are: 19h 34′ 45.2″ and +30° 30′ 59”.

The next Pn in Cygnus is one that is surrounded in controversy. Not because of being misclassified or because of strange properties that is has. No, it is because of its name. You see, in my 22″, I observe NGC 7008 and to me, it looks exactly like a fetus in profile (or as some English snob tried to straighten me out on IAAC chat – “feotus”). I would not call it this if it even began to resemble anything else but I as well as others, have totally agreed that the shape of this Pn looks exactly like a child in the womb. I know that this isn’t a fancy name like “Minkowski’s Butterfly” or “The Ghost of Jupiter” but come by my 22″ sometime this summer and I will show you what I mean. The Pn shines at 13.3 (P) magnitude and it is 86″ in diameter. The CS is relatively bright at 13.2. It responds very well to an O-III filter and the color is almost a pearl-white. The CS is where the umbilical chord should be; a faint star is there for the eye; and 2 brighter stars are where the feet are. There is a wealth of detail at higher powers if you take some time to observe it. The shape is well, fetus shaped! That’s all I can say. What do you think? You find this Pn at: 21h 00′ 32.8″ and +54° 32′ 36″.

Next we go to NGC 7048, a 1′ x 1′ oval of grey-white light. You can use low to medium powers to initially find and observe this one but pump up the power to try to detect some structure. “Owl eyes” can be seen at higher powers and s few faint stars touch the NNE and NNW edges. This is a really great object. Coordinates are: 21h 14′ 15.2″ and +46° 17′ 19″.

Another Cygnus favorite is NGC 6894. Be sure to use an O-III on this one as its surface brightness is low. It had a photographic magnitude of 14.4 and is 40″ in diameter. A central hole might be visible to you if you have the dark skies and use averted vision. Annular structure really begins to show itself pretty well at higher powers. SW and NW sectors are slightly brighter. No CS visible as it burns at 18.1 apparent visual magnitude. This is a great ring if you can observe it. Coordinates are: 20h 16′ 24.0″ and +30° 33′ 55″.

My final object for this “Indulgence” series is a neat little Pn with the designation NGC 7027. This is a 10.4 (P) magnitude, 14″ object. With an O-III and medium power, you should find it to be quite bright with a green color. The Pn seems to be stretched like NGC 6543 (“The Cat’s Eye”) with the western portion being much brighter than the rest of the nebula. At high powers, see if you can detect a box-like structure that has a distinct division by a dark lane. I have not been able to detect the CS which shines at 16.2, but seeing was bad when I observed this one. The coordinates are: 21h 07′ 10″ and +42° 14′ 10″.

One thing is for certain, you will now have many Planetary Nebulae to observe this summer if you take the time to get out and try them. You will be pleasantly surprised at a lot of these great dsos. It goes without saying that there are even many other great Pns such as NGC 6828 (The Blinking Planetary) in Cygnus, NGC 6543 (The Cat’s Eye Nebula) in Draco, Abell 50 in Draco, NGC 6210 in Hercules, Abell 46 in Lyra, Abell 62 in Cygnus, Abell 70 in Aquila, NGC 6369 (The Little Ghost) in Ophiuchus, NGC 6905 (The Blue Flash Nebula) in Delphinus, and IC 5148/50 in Grus.  I hope you too can find the sheer elation and indescribable enjoyment in the death of giant red stars as I do. Good luck!