Sunday, August 02, 2015

 

The (Sub) Urban Astronomer Night 1


If you’ve been with me for a while, you know I spent over twenty years under an urban sky in downtown Mobile, Alabama’s Garden (historic) District. Despite light pollution that at its worst could extinguish stars much dimmer than magnitude 3.5, I still wanted to observe from home—occasional trips to the club dark site and star parties weren’t nearly enough. So, shortly after I moved in at Chaos Manor South in 1994, I began  to survey the deep sky from my bright backyard.

At first, seeing much of anything other than open clusters under those conditions seemed a hopeless task. When you can only make out the three brightest stars in Ursa Minor, how can you hope to observe distant galaxies? But I persevered and eventually had surprising success. Not only did I conquer the entire Messier (even M101 and M74) from my backyard and similarly bad urban sites, I saw many objects from the NGC and more obscure catalogs.

What I saw of deep sky objects from the backyard of the legendary Chaos Manor South didn’t usually match what the objects would have looked like from good skies, but I had a ball anyway. I had so much fun I wanted to share my experience and my urban observing techniques. Which I eventually did in a book, The Urban Astronomer’s Guide. The Guide isn’t perfect, but I am still pretty happy with it today. Probably happier than I am with anything I’ve ever done. I still consult my own book at times, and that ought to tell you something.

If you’ve been hanging out here long, you also know that a little over a year ago I moved from downtown to the far western suburbs. Not only did I gain a mostly tree-free backyard, I went from magnitude 3.5 to a zenith limiting magnitude of 5.0 on clear winter’s nights. While a 1.5 magnitude gain doesn’t sound like a huge difference to newbies, old hands know that it increases the number of visible stars tremendously, and that the sky background in the eyepiece is much darker.

I had the occasion to pick up Urban Astronomer the other day after not looking at the book for a while, and after I got the information from it I was seeking, I got to thinking. My skies are better now, but they are still not perfect. Wouldn’t it be fun to go back through the The Urban Astronomer's Guide's list of DSOs and see how much, if any, better they looked from the new manse? I’d been seeking a visual project I could execute from my new backyard. Sounded like this might be it.

Going back through the urban objects would also give me a chance to share the tips and techniques I developed and/or employed for dealing with bright skies when you’re chasing dim objects. Over the years of working on Urban Astronomer—it began as a series of columns in my club newsletter in 1993 and didn’t become a book till over a decade later—I did a lot of thinking about and experimenting with what I called "city lights observing techniques," and developed some pretty strong opinions on everything from light pollution reduction filters to telescopes to star atlases.

Let’s start this first installment of the new project with a few preliminary tips. None of these is earth shattering; most are just common sense, but when you’re battling light pollution, whether from a red,orange, or yellow zone, forewarned is forearmed.

The size of your telescope, its aperture, is important. There’s an old urban legend (that’s appropriate) going around that says large aperture telescopes are useless for urban observing. That a big mirror gathers more sky glow than a smaller one and actually shows less of the deep sky. Nonsense.

Short and sweet? Set up a 12-inch and a 6-inch reflector side by side. You can even make  the 12 an f/5 and the 6 an f/8. Point ‘em both at Hercules' M13. In the 6, the Great Globular is just a bright blob. In the 12, even under poor conditions, it is a ball of tiny, tiny stars. If the sky background is too bright in the 12-inch, just pump up the power a little to spread out the background glow . All things being equal, more aperture always wins, and may be even more valuable in the suburbs than in the country.

Gain as much dark adaptation as you can. Even a little is better than none. There’s nothing you can do about light pollution—other than work to decrease it over the long run—but there is something you can do about ambient light, which is what mostly prevents you from gaining a modicum of dark adaptation, from allowing your eyes to become as sensitive to dim light as they can get. Begin by turning off your porch and other intruding lights, of course. If the people next door have lights on, shield yourself from them—it’s usually impossible to get people to turn off their yard lights, even for a little while, on a regular basis.

What I used to do was build stage flats. Frames of 1x4 lumber covered with muslin and painted black. Made stands for ‘em out of more 1 x 4s, and they could then be positioned as needed to shield me. Keeping ambient light out of my eyes and my telescope made a huge difference. This is so important that it wouldn’t be silly to consider building an actual observatory in your backyard. Really, one is even more helpful under bright sky conditions than under country ones. I would suggest a dome-type solution, since a dome will do more to block ambient light.

Baffle your telescope. I don't mean you should confuse the poor thing. More than a few Newtonians, especially imported Newtonians, are designed so that ambient light can enter the tube through the mirror end. A simple baffle like the one I cut out of paper in 5-minutes for my old Edmund Scientific Palomar Junior will definitely improve contrast.

Look for any places where ambient light can enter your optical system. If the telescope’s tube in front of the secondary mirror isn’t long enough, light is probably hitting that secondary and ruining contrast. Use plastic or paper or anything similar to extend the tube. This has the added benefit of helping keep dew off the secondary mirror.

Don’t be afraid of high power. In general terms, most amateur astronomers use too little rather than too much magnification under all sky conditions. Probably because when we were novices we were warned off “300x” by the veterans. For very good reason:  our imported 60mm refractors wouldn’t handle it. But your 8 or 10-inch telescope of today certainly will.

While it will make extended objects like galaxies and nebulae dimmer, higher magnification also spreads out the background sky glow and darkens the eyepiece field background, often making the target easier to see. Stars will not be spread out, so higher power will definitely increase contrast of star clusters.

Let me reiterate, keep ambient light out of your telescope and out of your eyes. Even if you’ve rigged up a light shield, it’s wise to go a step farther. Drape a black cloth over your head and your eyepiece. This will keep all the ambient light out, and that is particularly important when using light pollution reduction filters. If you allow light to enter the eye-lens of your eyepiece, the performance of any LPR filter, whether UHC, OIII, whatever, will be very adversely affected.

I often hear newbies say they are disappointed with their light pollution filters. That they don’t make as much difference in the backyard as they’d hoped. Part of the reason is the above. Filters, which screw onto the field lens end of an eyepiece, the telescope end, work by reflecting unwanted light away from the eyepiece. If you let ambient light enter the eyepiece from the eye lens end, it will be bounced right back into your eye from the “wrong” surface of the filter, the surface facing your eye, ruining any contrast gain you would otherwise have achieved.

Use light pollution filters, but understand their limitations. OIIIs, UHCs, H-betas, they all have their places in the backyard and can make the difference between seeing and not seeing dim nebulae. They can also reveal more details in the brighter objects, but be aware they are not a panacea. They do not work on everything.

Unfortunately, as many newbs are disappointed to hear, an LPR filter won’t do squat for a galaxy or a star cluster. Those objects are made of stars, and, unfortunately, the light of stars falls in the same range of wavelengths as the earthly light the filters are designed to reject. Some people will tell you a mild filter like the Lumicon Deep Sky will improve a galaxy by darkening the background sky without dimming the target object too much, but I’ve never noticed much improvement visually (mild filters can help with galaxies during imaging).

Wait for it…wait for it. Can’t snag M101? Wait for the best time. Wait for culmination, the time when the object you are chasing is as high as it ever gets, when it crosses the local Meridian, the imaginary line that divides the sky into east and west halves. Won’t do that over the course of the current evening? Come back when it will for a better shot. Even if an object is not very high when it crosses the Meridian, it is still as high then as it will ever get, and you will be looking through less air.

Also wait for those special nights, nights that are especially dry and clean, like evenings after a winter cold front has passed through and cleansed and dried the sky. Dust and humidity amplify light pollution, scattering any sky glow that is present and making things worse.

Finally, wait for an object to be positioned in the best part of your sky. If you’ve got a Wal-Mart to the east, wait till your prey begins to sink into the west. It’s sometimes the case that an area lower down in the sky might actually be better than the area closer to the Local Meridian.

Use a red light. It might seem obvious, but some newbies don’t grok that even in light pollution you want to use a red-filtered flashlight rather than a white one. Remember, you are trying to attain as much dark adaptation as possible.

How about those red-tinted "Astro-goggles" Orion  has sold for years? I tried 'em; sounded like a good idea. Not only would they protect my eyes from ambient light sources, I could put them on and run into the house if I needed to without blowing out my dark adaptation. Alas, not such a hot product. I didn’t mind that wearing them made me look like the king of the nerds, but they fogged up instantly even in the winter, and I was constantly tripping over stuff and bouncing off walls.

Use digital setting circles or a goto scope for object finding. While I am currently going through a non-computer “simplify” phase, there is no denying goto and DSCs are a godsend for the urban or suburban observer. If you can’t see many stars, it may be nearly impossible to find objects in star poor areas using a zero power finder like a Telrad. Even a 50mm finder may leave you lost in space.

You’ll be amazed what you can see of objects in the urban/suburban sky if only you can find them. For example, the first night I had my NexStar 11 GPS, I couldn’t resist giving her first light in the backyard of Chaos Manor South. Unfortunately, it was one of the haziest spring evenings in a while. Couple that with the light pollution of my red zone, and I didn’t expect to see galaxies. I keyed in M64, anyway, and when the goto stopped, I inserted my 12mm Nagler and had a look. At 233x, there it was, the good, old Black Eye galaxy. Not just visible, but showing off the dark spot, the black eye, almost as well as from the club site.

Use the same visual observing tricks you use from a dark site. Look away from a dim object instead of straight at it to bring your eye’s dim light receptors into play. Use averted vision, that is. Still can’t see your quarry? Jiggle the scope. The eye has an easier time seeing dim moving objects. Use all your standard tricks.

Most of all, don’t give up. Keep persevering and you will almost always be rewarded. No, you probably won’t ever see the Horsehead Nebula from your back 40, but it is more than likely you will eventually conquer M74 and the other hard Messiers. And many other besides. It took two seasons of trying before I picked up M101 from Chaos Manor South with my 8-inch f/5 Newt, but pick it up I finally did...

And so it was that on one recent evening that I again found myself out under a light polluted suburban sky with a telescope. Yes, the skies of the new manse are usually better, considerably better, than they were at Chaos Manor South, but not on this night. In addition to heavy haze and intermittent clouds—this has been such a lousy summer—there was a fat gibbous Moon hanging in the sky.

Seeing what the bright sky could offer up wasn’t my motivation for braving the bugs, anyway. My mission was to begin testing a set of eyepieces I am evaluating for a magazine article. That was exactly what I focused on for a couple of hours:  serious business. Once my work, which had been easy enough to accomplish in the horrible conditions—all I needed for ocular testing was the Moon, Saturn, and some bright stars—was done, I thought I’d have some fun. See what I could pick out of the mess.

Well, heck. How about M13? OK, but where was it? The telescope I was using this evening, as it has been on many recent evenings, was my low-tech GSO 10-inch Dobsonian, Zelda. She doesn’t have goto. She doesn’t even have DSCs; just a 50mm finder and a zero power sight. The problem was that the sky was now poor enough that I couldn’t make out a single star in the whole constellation of Hercules. The night had gone from “bad” to the proverbial “worse.”

“OK, then. No M13 or M92. What else?” I looked around. I could see the Dipper, but the idea of trying to find the Owl Nebula or M108, much less M101, on a night such as this seemed patently ridiculous. Out of all the “rules” I listed above, however, the one I’ve taken the most seriously is “Don’t Give Up.” If you want to be an urban or suburban astronomer, you have to banish “surrender” from your vocabulary. You will not go inside without seeing something. Well, I could see Vega shining bravely. If I couldn’t see the ring, I’d at least see the Double-Double.

I used the Rigel Quick Finder to position Zelda on the sapphire of a bright star. Then, looking through the scope’s RACI finder, I slewed across the little constellation, which was nearing zenith, to the two stars opposite Vega, Gamma and Beta, Sulafat and Sheliak. Once there, it was trivial to get on the Ring Nebula’s field. Since I was a boy, I’ve known the planetary nebula’s position well; it’s just about halfway down an imaginary line drawn between the two stars.

Nudged the scope one last smidge while looking through the finder (scope), and then put my eye to the 15mm 100-degree AFOV eyepiece. “OK, where are you, you little sucka?” One thing I remembered from my urban astro salad days was that you can’t always depend on even the brightest objects to jump out at you. Always examine the field carefully. I did that and there was M57, a somewhat ghostly smoke ring. Was it better in my 10-inch than it had been in my 4-inch Palomar Junior (which I often used in the early days of my urban observing)? Yes. Was it that much better? Not really. Frankly, it looked a lot like it does in this rather crude drawing from decades ago.

Conditions were so poor by now that even Zelda’s ten inches of aperture didn’t help much. When I added a UHC filter—I wanted to be sure the eyepieces I was testing were smoothly threaded for filters—the view improved a little. I could see that the center of the ring was filled with haze more easily than I ever could with my Pal, and I could pick up a few of the dimmer stars scattered across the field, but, no, it wasn’t that much better.

Which didn’t matter a bit. As I had been on so many city-bound nights, I was just bowled over to be able to see anything and surprised at how good a deep sky object could look under such atrocious conditions. I looked, and I looked, and I looked. Until a batch of real clouds shut us down. Had I seen as much as I would have on a clear, moon free night? Or from a dark site? No, not hardly. Had I had fun anyway? You betcha, and that is what matters most to me these days.

Comments:
Thanks for your light-pollution prisoner testimony. Gives strength to us mere mortals stuck in the near continuous twilight zones where we live. Northern VA requires a similar "never say die" attitude toward visual astronomy!
 
your book sits next to Luginbuhl and skiff "Observing Handbook" and it got me viewing from "in town". Don't go out to the old clubs dark sight much any more -old eyes and car lights at 3 am don't work well- but I still look at your book from time to time. Now when the mood hits, put my C8/LXD75 out, and use my d7000's intervalometers set to 60 images @ 30 seconds and about every 45 minutes go out and set a new subject and batch processing in the morning (let the computer do it while I'm doing something else). Without your book I might have sold my stuff but it kept me in the game.

A C8 on a LXD75/CG5 and a camera with a built-in intervalometers works great (and a LPR does help) in my 5.0 skies. Not how I expected my observing career to end but until the LXD dies that's my game plan.
 
Just came across this. Nice read. I found your section on DSCs and GoTo's pretty dead on. It brings to question this push of Dobs without setting circles at all as the most common first scope recommendation on some forums. It also makes me wonder how much of the sky these folks are missing because of it.
 
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