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.
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:
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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.
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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