Let's talk about planetary nebulae!

When I first got back into visual stargazing in 2001, one of the objects that was top on my list to re-discover and re-observe with my then largest telescope, a 76mm f/9.3 newtonian reflector, was a planetary nebula familiar to most amateur astronomers, M57, The Ring Nebula. I have always been fascinated with planetaries. However back in the day, when all I had was my trusty 40mm long focal length Celestron Cometron refractor, I was severely limited to only the brightest planetaries, M57 and M27. From my rather light polluted backyard in the 80's (back then probably red zone skies??!!), I spied a fuzzy star where M57 was to be. Yup no doughnut visage visible. The 3" reflector opened up a whole new world for me. The doughnut was not only there, it was rather bright too. And M27, the first planetary nebula to be discovered in 1764 by french comet ferret Charles Messier,  showed its dumbbell shape in my small scope. The nebula looked almost photographic in appearance after I obtained a Japanese made Orion SkyGlow filter in the 0.965" size. So began my love for planetary nebulae. With a narrowband filter, I began my quest to bag as many planetaries from my balcony observatory in Indooroopilly, and my dark sky site in Leyburn, Australia. Visually, mid sized planetaries were the easiest and showed the most detail. Large planetaries, such as the Helix Nebula in Aquarius, show up best in RFT's from dark sky sites with a narrowband filter. The most challenging of the planetaries were the small minute ones. These appear as tiny pinpricks no bigger than the stars themselves. The trick here is to "blink" them using a line filter such as a OIII filter. This is a trick used by advanced visual astronomers to confirm their quarry, since these filters dim the light from stars while allowing the light from the planetaries to pass through.

So what are planetary nebulae and how do they differ from supernova remnants? Well planetary nebulae are formed by stars that don't have sufficient mass to support a cataclysmic explosion to form a supernova. The usual suspects that puff out a shell of glowing gas after it has exhausted all its fuel are old red giant stars. Planetary nebulae are relatively short lived phenomenon, lasting only a few tens of thousands of years. As such they form all sorts of interesting shapes, some of which are visible to visual astronomers. Below are a selection of planetary nebulae that I have sketched and imaged. I have included a description of them and how to appear visually in a scope.

M57: The Ring Nebula, Magnitude: 8.8 Size: 230" x 230" (Lyra)

Discovered by Antoine Darquier in 1779, and a month later by the famous Charles Messier, this is one of the showcase planetary nebulae you see in the textbooks and observing manuals. Indeed it is one of the brighter and showier objects for beginners to deep sky observing. I remember seeing this object for the first time in my Cometron 40. It was nothing more than a blurry star. Probably due to its lack of light gathering power, no amount of magnifying allowed me to see the celestial doughnut visage. Years later, in 2001 to be precise, I saw this same object, as it should be seen, in my 76mm newtonian a ghostly ring of smoke! Now with several tens of years of visual observing under my belt, I can spot this object and make out its hollow tube visage even in a 60mm refractor. To see the inside of the hollow illuminated by ghostly luminiscensce you need at least an 8" scope. This object is even detectable as a out of focus star in my 8x40mm binoculars from dark sky sites. An easy object to image too!

M57 at 1000mm 102GT, DSI II

M57 at 400mm 70TS, DSI II

Sketch of M57 at 166x in the 6"

M27: The Dumbbell Nebula Magnitude: 7.5; Size: 8' x 5.6' (Vulpecula)

The first planetary nebula to ever be discovered, this is one of the few planetaries that looks like a planetary in small instruments. If all you have is a small pair of binoculars (most commonly available garden variety 7x50mm binoculars), this is the planetary I would recommend, since it is large and bright enough to cut through light pollution, and unlike the other smaller ones, this actually looks like its namesake! Through the telescope, it starts to strut its stuff, appearing almost photographic in appearance, with the help of narrowband filter of course. To me the nebula looks more like an apple-core from light polluted sites without a filter. Under dark skies, with a narrowband filter, this same nebula looks more like a football than a dumbbell or apple-core. What's cool about this nebula is you can actually see the background stars shining through the nebulosity!

M27 at 1000mm 102GT, DSI II

M27 at 400mm 70TS, DSI II

Sketch of M27 in at 47x the 6"

M76: The Little Dumbbell Magnitude: 10.1 ; Size: 2.7 x 1.8 arcmins (Perseus)

This is one of the supposedly harder objects to spot in the Messier list and one I had never seen due to its very northerly location. I found this object "easy" even from white zone skies in Los Angeles in my 6" (and later discovered that this object was also visible with a filter in my 102mm GOTO refractor), and this without the use of a narrowband filter. I guess the imposing visual magnitude discourages beginning observers from even trying. While it was "detectable" without the filter, I found the views to be vastly improved with the use of my DGM NPB narrowband filter. The views were even better when I obtained a OIII line filter! Appearing as a bar of light, this object need high magnification to do it justice. Imaging this was also ridiculously easy, and the CCD brought out the colors in the object!!!!

M76 at 1000mm 102GT, Meade DSI II

M76 at 400mm 70TS, Meade DSI II

Sketch of M76 at 37x in 6" and 50x in the 102GT

NGC 7293: The Helix Nebula Magnitude: 7.6; Size: 25' (Aquarius)

The largest and brightest of the planetary nebulae also happens to be one of the hardest ones to detect from light polluted locales. This is due to the fact that the object covers a very large portion of the sky and has a very low surface brightness. This is one object that is greatly enhanced by narrowband filters, and looks the best in very wide field instruments. This object is now detectable even from red zone skies with the help of OIII filters. Imaging wise, this is a brilliant object as it is so big. Color is also very evident, even with 30 second exposures!!!!!!

Helix at 400mm 70TS, DSI II

Helix Nebula at 56x in the 6" 

NGC2438 in M46 Magnitude: 1.8 ; Size: 1.1 arcmins (Puppis)

This is another very interesting planetary nebula that shows abundant detail in small scopes. Found in the southern constellation of Puppis, but high enough for northern hemisphere skywatchers to pick up, it is superimposed on the open cluster M46. Physically they are not associated, but they do make a very pretty pair. Greatly enhanced by the use of a narrowband filter, this one is large enough to not require too much magnification. Imaging this one required me to use a broadband imaging filter due to its altitude in the sky.

M46 and NGC2438 at 500mm 102GT, Meade DSI

Sketch of M46 and NGC2438 at 70x in the 6"

NGC7009: The Saturn Nebula Magnitude: 8; Size: 41" x 35" (Aquarius)

The famous Saturn Nebula does not reveal its secrets easily. I though I spied its famous ansae at 300x in my 10" dob, but that is a big "if" (big part of this is the seeing...and lil turbulence blurs this). Looking more like an bloated elongated star in smaller scopes, I have also yet to capture the "rings" using my 102GT at 1000mm.

Saturn Nebula at 1000mm 102GT, DSI II

NGC2392: The Eskimo Nebula Magnitude: 10.1; Size: 48" x 48" (Gemini)

This is another brilliant lil one that shows abundant detail in larger scopes. Visually I have detected the outer parka, and the subtle triangle in the central region making out the eskimo's face in my 10" at magnifications in excess of 300x. This same feature cannot be made out in the 6", but the outer parka is visible. Photographically I have been trying to get the exposure right to highlight its internal detail. All I have gotten so far is an outer and inner ring without any internal detail at 500mm focal length in the 102GT.

Eskimo Nebula at 500mm 102GT, DSI I

Clockwise: Eskimo Nebula at 400x in the 10", at 156x in the 6" and 70x in the 6"

NGC6818: Little Gem Nebula (Sagittarius)

This is another bright but small planetary that does not show much internal detail even in a 10" scope, but it does show a disc at higher magnifications. Color is evident visually in scopes 6" and larger. The best CCD image I have of this brilliant planetary was with the 102GT at 1000mm focal length, showing a nice lil green disc. 400mm just does not do justice to this object!

NGC6818 at 1000mm 102GT, DSI II

NGC7008: Fetus Nebula Magnitude: 12; Size: 1.4' x 1.1' (Cygnus)

Never knew what I was missing with this one. Amazingly bright and rather large, it is one of those you want to "scrutinise" at higher magnifications, if you have sufficient aperture. I have still yet to train my bigger scopes on this lil beauty. That said it looks pretty even in a 4" scope. CCD imaging brings out a whole level of detail. Even with my 70mm TS OTA there is abundant detail in this object. I need to re-image this at full focal length to see if I can get more detail out of this object.

NGC7008 at 400mm 70TS, DSI II

NGC3242: Ghost of Jupiter/ CBS eye Magnitude: 8.6 ; Size: 25" (Hydra)

One of the planetaries that actually looks like its namesake, this is a fairly large object which shows abundant detail in large apertures. Also known as the CBS eye, this curious feature is actually doable in apertures as small as 10". I have seen this at 300x magnification! This same feature is invisible in my C6! Have to try for it in my C8 next time I have a look at this. Imaging this with my Meade DSI II OSC was a lot harder than I though due to overexposure. I am still coming to grips with getting the exposure correct for the more compact and high surface brightness planetaries.

Clockwise: NGC3242 at 400x in the 10", 112x in the 6" and 56x in the 6"

NGC5189: Spiral Planetary Magnitude: 8.2; Size: 90 x 62 arcsec (Musca)

A strictly southern hemisphere object since this DSO is found in the small constellation of Musca, the fly. I remember my first views of this object through a SAS member's 16" truss dob (thanks Kevin Dixon!!) and though I was looking at a very detailed spiral galaxy!!! I later found out that this was a planetary nebula, and a very pretty and unique one at that. Also I discovered that it was bright and showed a lot of detail even in my C6 scope., even from light polluted Brisbane!!! Since it is a planetary nebula, it is greatly enhanced by narrowband filters. I have gotten great views of this in my 6" and 10" scopes even from red zone skies with the filter screwed on. A must see object if you are ever in the southern hemisphere!!!! Just wish I had a CCD cam and a tracking scope back in oz. This would have been an excellent subject to shoot!!!!!

Sketch of NGC5189 at 56x in the 6" 

NGC3132: Eight Burst Nebula/ Southern Ring Nebula Magnitude: 9.87; Size: 62" x 43" (Vela)

Technically this is still visible from the southern states in continental USA, although I have not tried to pick this up just yet. This was one of my favourite planetaries while living in Queensland, Australia, ranking right up there with M57 and M27! Big and bright, this one too needs magnification to do it justice, showing its multi-shell appearance at higher powers in my 6" and 10" scopes. In the 4.5", I can just make out its ringed appearance, although the multiple shell appearance eludes me. Like the rest of the mid sized planetaries, this also looks good from light polluted skies. All that is needed is higher magnification, or the use of a narrowband filter. Wish I could capture this on CCD! Maybe when I visit my old stomping grounds in the future!!!!

Clockwise: NGC3132 at 400x in the 10", 112x in the 6" and 56x in the 6"

NGC6302: Bug Nebula Magnitude: 7; Size: 3' (Scorpius)

This is one of my favourite southern planetaries, and also one which is visible from the northern hemisphere. It is brighter and exhibits more detail that most people realise, showing an elongated bar, with a pinch down the middle. Imaging this object with the Meade DSI II requires a SkyGlow Imaging filter as this object, while not a horizon skimmer, does not cumulate very high in the night sky. Visually, I find I can push the magnification pretty high on this one. Also does very well with a UHC or OIII type filter visually.

NGC6302 at 400mm 70TS, DSI II

Sketch of NGC6302 at 93x in the 6"