Sunday, May 20, 2012

 

My Favorite Fuzzies: M17, The Swan Nebula


There are some deep sky objects we hold dear from the beginning, muchachos. Most of us looked at the M42s and M13s early on, kept coming back to them, keep coming back to them, and have known them like the backs of our hands for our whole amateur astronomy careers. Then there are the ones that grow on us. With me that’s M8, M101, and M17, the Swan (a.k.a. Omega) Nebula.

My first look at M17 was from Mama and Daddy’s backyard the summer of my Palomar Junior 4.25-inch Newtonian reflector. The nebula is remarkably bright, certainly, at magnitude 6. 0 or so, but it didn’t impress me. It was low down in the south, and trees and the lights of the main body of our subdivision made it not much better, if any better, than the even lower Lagoon Nebula, which I didn't like much as a sprout either.

All my 1960s logbooks are gone—with the exception of one single page, my drawing of Copernicus—so, alas, I can’t give you my first impressions of The Swan verbatim. I do seem to recall it didn’t look a dern thing look like a swan or an omega no matter what the books said or how I held my mouth as I squinted into my Kellner eyepiece. All I was seeing in my Pal was the Swan’s body, which was nothing more than a short “dash” of dim light, a barely visible streak in the 1-inch (25mm) Kellner.

I’d expected a little more for my effort, since I’d found the nebula kinda trying to track down among the subdued stars near Scutum, but, well, it was what it was, and it wasn’t the only deep sky object, I was sadly realizing, that didn’t look as good in the eyepiece of my 4-inch as in the pictures from Mount Palomar.

Before we go further, let’s do the “just the facts, m’am” thing. M17, NGC 6618, The Swan Nebula, was probably discovered by Philippe Loys de Chéseaux in 1745, but his observations didn’t get much publicity, and the nebula was independently discovered by good old Chuck Messier almost twenty years later on the evening of June 3, 1764. Our pals William and Caroline Herschel had a look at M17 with their big guns, but the first person to comment on its odd shape seems to have been Willie’s son, John, who in his log entry said,  “The figure of this nebula is nearly that of a Greek capital omega, Ω, somewhat distorted, and very unequally bright.”

M17 is situated in the deep summer constellation, Sagittarius, which makes it a little low for observers at mid-northern latitudes, but at least it’s in the more northerly part of The Archer, almost over the border and into Scutum, the little constellation near the tail of Aquila the eagle.

How far away? Like most nebulae, the distance to M17 isn’t well known, but it is thought to be about 5,000 – 6,000 light-years from our pebble in the sky. Like the Orion Nebula and the nearby (and far more subtle) Eagle Nebula, M17 is a place of star birth, and the swan shape is just the brightest section of a huge complex of nebulosity.

Being a Messier, it shouldn’t surprise anybody that M17 is considered a “showpiece” object, whatever the hell that means. It is easy in surprisingly small telescopes—it is a treat in my Short Tube 80 under dark skies. It responds well to a UHC nebula filter, and the more aperture you can pour on, the more you will see. It is detail rich, being crisscrossed by dark lanes and spots. As above, it is just the brightest part of a huge cloud of nebulosity that in the deepest images looks more like a football than a swan or omega. 

It was nice to capture another Messier, but I didn’t linger; I just checked M17 off on my list and moved on. Like a lot of novices who’ve just found their deep sky feet, I was more interested in hunting than I was in looking. Unless an object was truly spectacular in the M13/M42 mold, I might give “the new one” a minute’s examination before I was on to something else.

Did I revisit M17 during my Arkansas sojourn, the years when I was stationed at Little Rock Air Force Base? I must have, but I don’t remember it. No doubt M17 would have looked far better from the rural Arkansas skies of the 1970s than it had from The Swamp, and my 8-inch Cave or the Orange Tube C8 that followed it would have brought the Swan’s neck into stark view. But at the time I was more interested in tackling Virgo-Coma’s galaxies and getting going with deep sky astrophotography than I was in looking at dumb old Messiers again.

The next time I paid Miss Swan the attention she so richly deserves? After I moved back to The Swamp in the early 1980s and thought up another one of my (sometimes slightly wacky) observing projects. I’d do the Messier, all the Messier, including M101, M74, and the rest of the list’s birds of ill omen from my light polluted backyard whose skies were every bit as sodium-streetlight-orange as Chaos Manor South’s are today.

The amazing thing is that my backyard quest for the Messiers turned out not to be as ridiculous as it sounds. By waiting till Ms culminated, and waiting for “special nights”, I got them all fairly quickly. How did my observation of The Swan compare to what I’d seen from Mama and Daddy’s considerably better backyard?

It was better, but not that much better. I had a larger scope and more experience, way more experience, under my belt, but like most nebulae, especially southern nebulae, M17 cries out for dark sites. It was pretty enough, and since I had a better idea how to attack faint stuff, I thought I could see the neck on good nights. But usually M17 was just that same old boring streak of nebulosity.

After my backyard Messier survey, whose observations went on to form the heart of my book, The Urban Astronomers Guide, I didn’t get back to The Swan for a few years, not till I began observing from the Possum Swamp Astronomical Society’s old Hurley, Mississippi dark site.

At the time, the PSAS was blessed to be under the leadership of one of those rare amateurs who can almost magically transform a sleepy little astronomy club. Whose excitement for the night sky is, yes, infectious. David wasn’t just on the cutting edge gear-wise—he bought an LX200 (Classic) the minute they became available—he almost singlehandedly put together a pretty good club newsletter, writing and printing it on, shazam, one of them new-fangled IBM compatible computers. And he undertook the usually thankless job of Club President.

Yep, David was a go-getter, and the first thing he set out to get was a new dark site for us. Clubs tend to wither away if there is no group observing under an at least half-way decent sky, and he was not about to let that happen to the PSAS, who’d been without a good observing location for a while. David made friends with a young farmer who had an unused patch of a field in the tiny community of Hurley.

The field was perfect for us, fairly secure, fairly dark, and only about 45-minutes from town. But it was not perfect. It was situated right next to a big pond, and all spring and summer played host to legions of vampire-class skeeters. The fire ants sometimes got out of control, too, building enough mounds to make the observing field a mine field.

As a matter of fact, a PSAS member who liked to use his telescope while he was moderately to heavily tipsy ran afoul of the fire ants and suffered some damage to himself and to his pretty TeleVue Genesis refractor one night. He punctured a nest with a tripod leg, causing his scope to tip over and the ants to attack him with their accustomed ferocity. It was hard not to laugh at Gomer doing the chicken dance across the field trying to shake off the critters, but I stifled myself. Fire ants can be serious business, and have put more than one person in the hospital—or worse.

As y’all know, it is not unknown for me to get spooked at a dark site when I am there all by my lonesome. That was just as true in the Hurley days as it is now. If anything, that site was more lonely and isolated than the current PSAS observing field. There was also a real cause for concern, since this was at the dawning of the meth trade, whose explosion left some formerly peaceful country spots more dangerous than inner-city slums. I could usually depend on one other person being on the site with me, but not always. President David had a pretty rigorous work schedule, and the club was in transition, with a couple of our most enthusiastic observers having moved away.

I had two things going for me on the evening I went Swan hunting. One was my Walther PPK—not that I ever needed it for anything other than emotional reassurance. The other was that it had been several years since I’d been able to observe from a dark site and was not about to be robbed of the deep sky delights by a cotton picking case of the nerves. To be honest, though, I was relieved rather than put out to be blinded by the approaching headlights of the cars of a couple of PSAS members just after dark.

The area to the northwest of Possum Swamp can still offer some good views, but our Hurley site to the southwest has been compromised by the construction of a huge truck stop on I-10 just south of the dark site. The final nail in the coffin was the coming of the Mississippi Gulf Coast casinos with their neon signs and their laser light shows. But in the early 90s the heavens were still surprisingly dark and deep. Which was attested to by me mistaking the summer Milky Way for incoming clouds on this night.

The Telrad, an Orion/Vixen 25mm Kellner, and Sky Atlas 2000 eventually got my brand new Coulter 8-inch on the field of M17, but it seemed just about as hard as when I’d been a kid. The Swan was one of the objects I found more difficult to find than I thought it should have been.

There are certainly plenty of stars visible in its area of Sagittarius to hop to The Swan from, but that never helped. I’d always be saying bad words well before I found the nebula.  Winter’s M37 is another “easy” one that would get me to spouting fire and brimstone in the pre go-to days. Don’t ask me why. Back when my ‘hopping skills were at their peak, I thought nothing of tracking down the dimmest sprites of NGC galaxies, but M17 and M37? Katy bar the door!

When I finally found The Swan, the first thing I focused on was the “neck,” which had eluded me as a sprout. This curving arc of nebulosity, which is also the omega if you see a Greek letter here, was unmistakable. Both it and the “body,” that dash of nebulosity leading away from it, were visibly crossed by dark lanes, just like in the pictures. I looked and looked, hoping to catch some of the outlying clouds that litter the area. No dice. That would have to wait for darker skies and maybe more aperture, I reckoned.

My logbooks from the 60s and 70s are gone, but I still have those from the 80s and 90s. My impression of the Swan on that hot August night in 1993?

Despite relatively poor skies (scattered clouds/haze), M17, The Swan Nebula, is bright. The neck is easy to see and the nebula shows dark details, including a lane that cuts the "body" in half. This was first light for the Coulter Odyssey 8-inch f/7, and it performed well and got quite a few favorable comments regarding its optics.

The sky at McComb, Mississippi’s Percy Quin State Park was at least a little darker than that of Hurley in 1994, but what made most of the difference was indeed extra aperture. If you are a novice, you’ve likely heard the silverbacks in your club recite the mantra:  “Aperture Always Wins.” That’s true, all things being equal. All things are not always equal, but there is no doubt going from 8-inches to 12.5-inches allowed me to see a lot more of M17 on my first dark site run with the Dobsonian that was eventually to become known as “Old Betsy.”

But aperture is sometimes only part of the equation. Given the DSRSG’s mid-fall date, M17 was darned low by the time it was dark. Even 12-inches should have been hampered. It was not. The neck and body were just like they’d been on that good night in Hurley, only moreso. The Swan wasn’t just brighter, more dark lanes and patches all along neck and body swam into view. The body of the bird actually began to look more like a fish, with a V-shaped "tail." Mer-swan? The frosting on the cake was that holy grail of Swan watchers, the “external” nebulae, the patches of nebulosity away from the main body. An elongated spot just above the Swan’s head was particularly easy to see.

And that was it for the old crow for a while. Till I decided I’d try CCD imaging again. For the second time. The first time had been something of a disaster. I got absolutely nowhere; the resulting CCD images I got after a lot of blood, sweat, and tears were decidedly worse than my 1990s vintage film astrophotos.

The reasons for that were several, but mainly it was that a dozen years ago affordable CCD cameras, those that hovered around the one-grand level, had very small imaging chips. “Web-cam size” we’d call ‘em today. That made it incredibly difficult to get targets in the field, since I was using Celeste, my Ultima C8, on her original fork. She had no go-to and no digital setting circles. If I’d a-had good sense, I’d have bought a set of DSCs before the camera. But I was so excited about the “CCD revolution” that all my mates were talking about and joining that I couldn’t restrain myself. I bought a Starlight Xpress MX5, and had at it. How hard could it be?

The MX5 was really not a bad camera for the day, it just wasn’t much fun to use. I’d spend hours in the backyard the summer I got it, come in hot and frustrated and snapping at everybody, and usually wouldn’t have much to show for it. Even though it wasn’t great shakes on the deep sky, the MX5 was capable of taking pretty good planetary images, and if it had only had color I’d have kept it for that reason. It didn’t, so just before the big Mars opposition of 2003 it went on Astromart and I bought a SAC 7b.

The story of the SAC camera, made by a tiny outfit down in Florida, is one I ought to tell y’all some time, but suffice to say it was a modified color webcam with a Peltier cooler and could take outstanding images of the Moon and planets. Deep sky? Its chip was even smaller than that of the MX5, though I did get recognizable shots of M57 and M13. I contented myself with imaging The Angry Red Planet, Jupiter, Saturn and the Moon with the SAC 7, but once Mars had sailed away, I felt the call of the Great Out There again.

Not that I was planning to buy another CCD camera. Till I got a call from my old pals at Anacortes Telescope and Wild Bird. Seems as they’d just got a shipment of the new Meade DSI CCD cameras. The DSIs were in short supply, and they were holding one for me. Wouldn’t I like to send them my credit card number?

The thing wasn’t much more than 300 bucks, so I didn’t see why not. Oh, I did a little resisting, but eventually stingy old me was won over by Meade’s COLOR camera, which had an at least somewhat bigger chip than the SAC, and reputedly had software that would allow you to “Get great pictures the first night out!”

Was that true? Meade has been known to use a little hyperbole in their ads, but for once it was. Yes, the software was kinda complicated. It did EVERYTHING except cook your supper, helping frame and focus and guide and process. It took me a night or three to figure out how the hell to work it; that’s for sure. But when I did, I finally began getting the CCD pictures I’d dreamed of. They were at least as good as the best of my film astrophotos and they dern sure were easier to get.

Not only was the DSI more sensitive than the MX5, I was able to stop worrying about drift polar alignments and guiding. By now I had my Celestron CG5 GEM, which had a built in polar-align routine. If I used that, I could take 30-second – 1-minute exposures with the C8 at about f/4 without guiding. Even better? The DSI would automatically stack my short subframes into a finished image—on the fly.

That was what Meade’s somewhat confusingly written manual said, anyway. I doubted the dang thing could possibly work like they said, but I intended to find out. One early summer night I dragged the Toshiba laptop, the CG5, the C8, and the DSI out to the in-town observing site which was all the PSAS had in the mid-oughts. Our once enthusiastic President Dave had burned himself out like a meteor in the mid 1990s, stepped down from his office, and soon dropped out of the club and amateur astronomy altogether.

Since none of us were acquainted with the farmer who owned the land in Hurley, we felt funny about continuing to use the site. Especially after we went one rainy summer without getting out there even once. Instead, we began observing from the same place we held out meetings, the public schools’ Environmental Studies Center. It had started life twenty years before in the midst of reasonably dark suburbs, but eventually even slow growing Possum Swamp had expanded enough to make its skies badly light polluted. But wasn’t that part of the supposed CCD allure? That you could get reasonable deep sky images from putrid skies? We’d see.

Hokay. Set up the CG5, aligned it, did the polar alignment procedure with the hand control. Removed the eyepiece and diagonal, screwed on the Meade f/3.3 focal reducer and mounted the DSI. Next step was picking a target.

Why M17? I figured it would damn sure show what my 300 buck CCD camera could do. While reasonably well placed in a somewhat darker part of the ESC sky, The Swan was low and it was hazy over thataway. After a little twitching of the focus control, the stars around the nebula, which was weakly visible with a few seconds of exposure, were good and sharp. I did a Preview 30-second test, adjusted the image histogram, and told the computer to take 30-second exposures till I told it to stop and to stack those that were of good quality. I clicked on a bright star to serve as the software’s alignment reference and let ‘er rip.

While the DSI did its thing I tried not to worry about the picture “developing” on my laptop’s screen, stealing worried peeks at the computer every once in a while. What I was seeing actually seemed to look pretty good. When we were done? The Swan would certainly need some processing with Adobe Photoshop—or with the antique but fairly effective image processing program that shipped with the DSI. But, not bad, not bad at all.

The color image above was the result, and the fact that I can still stand to look at it today says that—given my humble requirements—it is indeed OK. If there is a single fault to it, it is that it is overprocessed. I was just learning the difficult art of image processing, and tended to do too much rather than too little.

Back then? I was as happy as a schoolboy, I was as giddy as a drunken man. Not only was the swan shape as clear as day and as red as a glass of Chianti, I could finally “see” all that elusive nebulosity with my own telescope! I’ve since gone on to take video images of M17 like the black and white one here with even greater ease, and I’ve done “stills” with my DSLR and ST2000 CCD camera that far exceed the quality of that first humble M17 snapshot. But maybe I still love that DSI shot best—it was the CCD breakthrough I’d needed.

I’ve gone on to get better visual looks at M17, too. Since the 12-inch Dob is still my BIG GUN, though, that’s required better eyepieces and, most of all, light pollution reduction filters, UHCs and OIIIs. Come to think of it, maybe it is finally time we talk about LPR filters muchachos. Why don’t we do that Sunday after next?

Next time:  The Herschel Project Night 33…

Comments:
"By waiting till Ms culminated, and waiting for 'special nights', I got them all fairly quickly."

I'm impressed that you accomplished this. I've had nothing but frustration looking for low-surface-brightness objects from suburban/urban skies (limiting magnitude ~4.5 - 5.0). I have yet to see M74 or M101 from my deck, despite low levels of glare.

These days I put most of my efforts into objects with higher surface brightness -- globulars, open clusters, compact nebulae, etc. I saw M59 and M60 last night, so some galaxies can make it through.

Someone ought to draw up a thorough list of objects that can be seen through light pollution. I've found they can be surprisingly faint, as long as they are compact and take magnification well. Maybe call it the "Urban Astronomers Catalog" or something. :-)
 
I did that very thing a few years back in _The Urban Astronomer's Guide_ (Springer)... ;-)
 
Rod wrote: "I did that very thing a few years back in _The Urban Astronomer's Guide_ (Springer)... ;-)"

Yes, my comment was meant to be very tongue-in-cheek. Surely you didn't think that the similarity between "Urban Astronomer's Guide" and "Urban Astronomers Catalog" was a coincidence?

Humor doesn't translate well via HTML!
 
At o-dark-thirty in the morning, I am not at my most perceptive. LOL.
 
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