September 28, 2016: My Local Dark Site Ain’t So Dark, and Three Tough Messiers

It looks like the sky has cleared at last.  My long national monsoon nightmare is over.  So I got off my ass and took my scope out to my “local dark site”, the aptly named Creekside Park, which I had scoped out (pun intended) a few weeks ago.  This is a nice, grassy, tree-studded park, about half a mile from my apartment.  It’s reasonably dark.  And by “reasonably”, I mean kinda sorta.  This park is ringed by streetlights; it has office buildings all around, including a pair of “big” ones (by Denver standards, anyway, heh heh) off to the east that pretty much block the sky for about 10 degrees above the horizon in that direction.  Doesn’t sound like a great observing picture that I’m painting of this place, right?

However – you knew there had to be a however in there – with the exception of that 10 degrees to the east , where I wouldn’t really be observing anyway, I basically do have the entire sky open to me, so that’s pretty good.  And the trees do a halfway decent job at blocking out some, but not all, of the streetlights.  Depending on where I set up in the park, I can be relatively sure of not being shined down upon by them directly.  On the other hand, this will be problematic for almost half of the year as fall approaches and these trees start losing their leaves, going hand-in-hand with losing their ability to block out the streetlights.  So as “not dark” as it is now, it’s only going to get worse.  Not good.  Not to mention that I gotta pack up a shopping cart with all the gear – the scope, the tripod, the observing chair (oh, did I forget to mention that I have an observing chair?  More later), and wheel it all the way out there. So, it’s not a grab-and-go location by any means.  My limited southern view balcony will have to continue to serve in that capacity, and basically only for the moon.  Or will it?

To me, the key to observing in light-polluted skies (hey!  That’s what this blog is all about!) is dark adaptation.  There’s nothing that can be done about Denver’s sprawling light dome high above my head – except to get far, far out of town.  As I described when I watched the Perseids in 2015, it takes a loooong time for your eyes to adapt to darkness.  Yes, your pupils fully dilate within a second or two.  But the chemical reactions in your eye – the buildup of rhodopsin on your retina, to allow your eyes to become more and more light-sensitive and to truly adapt to the darkness – are cumulative, increasing your ability to see dimmer and dimmer sources of light for up to around half an hour.

The only way to achieve good dark adaptation is to get away from all sources of ground light shining into your eyes.  And by all, I do mean every single one, because one is all it takes to ruin your dark adaptation.  And that means, primarily, getting away from or blocking out all streetlights.  I was able to do this very well on the roof of my apartment building back in New York.  Being 17 stories above the street is definitely getting away from streetlights – and car headlights, and building security lights.  However, the light pollution in Manhattan is so god-awful that even on the, ahem, darkest nights there,  the skyglow made it so bright that I could always just about read my observing lists off of the back of the envelope I had written them on, without any additional light.  As I said during that first Perseid report in 2015, it took me a while to get sufficiently dark-adapted to be able to see Albireo, shining high in the sky at a relatively bright magnitude 3.05.

Here at Creekside Park, I could definitely see Albireo easily.  But I couldn’t really go much deeper than that visually, because my observing spot is about a hundred yards or so off of a well-travelled roadway, and the park is ringed with all those streetlights.  I just can’t get completely dark-adapted there.

When I went out there last week it was pretty clear for a while, with some clouds rolling in and out over different parts of the sky.  I was able to see M22, and it was pretty good.  I scanned around some of the other Sagittarius-area gems, M11, M8, M20, etc., and of course M13 and M92.  Everything was nice.  Nice.  Not thrilling.  Nice.  Nothing like how they appeared at the DAS dark site, of course, but still looking good for so close to home.  I was planning on staying out past midnight to check out the Pleiades, Andromeda, and the rising waning gibbous moon, but high clouds rolled in around 10:30, and I called it quits.

I have to say though that I was mildly disappointed with Creekside Park as a local observing site.  I left feeling like I needed a better location, one that was darker.  I have the cart.  As long as I’m loading it up with all my stuff anyway, it doesn’t matter that much to me if I have to haul it around for a ten-minute walk or a twenty-minute one.  However, after checking out a few of the local parks within about a mile of my place, they’re all pretty much the same:  ringed by streetlights, or with park pavillion lights that never turn off, or with cars driving by, shining their headlights directly at any observing spot.  Each one was really no better than the last.

But this may all be for naught because – shhhhh, don’t tell anyone! – the door to the roof of my apartment building somehow became unlocked!  I swear I had nothing to do with it, but I was thrilled!  Up I went, easy-peasy, two trips, one with the scope, the other with my new observing chair, up a couple flights of steps.  And it is nice and dark up there.  The key thing, the thing I’ve been discussing, is to get away from all sources of light.  This roof does that very well.  It is above the streetlights and parking lot security lights that normally shine right into my face from everywhere else in my neighborhood, including and especially, right in my face off of my balcony, as they are attached to the building on my floor.  And, there’s a three-foot high fence all around the roof that blocks even more light from other parking lots and such when I’m sitting down at the scope.

There are drawbacks, however.  There is no westerly view whatsoever, as that’s blocked by the rest of the sixth floor of the building, right behind me.  But then again, who cares what’s in the west?  That’s all the stuff that we’ve been looking at for the past three months anyway, so good riddance.  On the other hand, the east and south are wide open, and that’s where all the good, new stuff comes from.  The north isn’t too bad, and overhead is good and clear as well.

Another drawback is that there is a gigantic vent on the roof that pushes air in and out of the building on a timer every half hour or so for about three minutes at a time.  There’s no warning, so it just starts up instantly, REAL LOUD, and instantly activates my startle response.  Bigtime.  So much so that I gotta be careful not to shoot my eye out if I’m looking through the scope at that moment.

Hopefully, my roof access will continue.  In the meantime, the viewing there was excellent; noticeably better than at Creekside Park.  Well, in any case, it’s far better than the sky I’m used to off of my previous rooftop in Manhattan.  I was trying to estimate my limiting overhead magnitude, which is harder than you might think when you’re seeing all these dim stars for the first time.  I was seeing 4 out of the 6 stars in Orion’s shield, and most – but not all – of the stars in Gemini.  I would say it was right around 4.0, give or take a tenth, so I’m thinking that I’m able to go about a full magnitude deeper.

Oh, did I forget to mention that I was observing at 3:30am?  Yup.  I had been helping a friend move, and I was still pretty wired.  I got my first glimpse of the Orion Nebula of the season, and let me tell you, it was glorious.  No need for my Orion Ultrablock filter; I was seeing just gorgeous textured nebula clouds there, bright and sharply defined.  That extra magnitude deeper really helps.  The 4th star (B) of the Trapezium was trivially easy to see.  I tried mightily to see the E and F stars at 10.3 and 10.2 magnitude, respectively.  I used my TeleVue 8mm Plossl to bump up the magnification to 193x, and stared and stared, averted vision and all, but no dice.  Ah well, something to look forward to trying again this winter as Orion rises higher in the sky.  I never tire of the Orion Nebula.

I checked out Gemini and Auriga’s four Messier open clusters, M35 through 38, and they all looked a good bit more filled out with that extra magnitude of light.  The Pleiades were their usual bright selves, but still no hint of any nebulosity, even though this time I was, ahem, looking in the right area.  And no Milky Way anywhere to be found, so it wasn’t that dark.

And I bagged THREE NEW MESSIERS!  It’s one thing to find new Messiers from a dark site; that’s easy!  It’s something else again to find them from home under light pollution.  I went for M78, an 8th magnitude nebula in Orion, not too far from Alnitak and the area of the Horsehead Nebula.  This is an object that was well-nigh impossible from Manhattan.  Then I went for M79, an 8th magnitude glob not too far off in Lepus.  Both of these were dim, dim, dim.  M78 was just a very faint little patch, barely distinguishable from the background sky.  On the other hand, I could just tell that M79 was a globular cluster, albeit an exceedingly dim one.  And then I remembered another Messier that was out that I had never seen – my old nemesis – M1!!!

It was well after 4am by the time I looked for the Crab Nebula.  It was elevated high up in the sky, at least 60 degrees above the horizon, giving me my best chance to see it in terms of not being dimmed by atmospheric extinction.  Because it was so late, I was also giving myself my best chance in terms of there being the absolute minimum light pollution possible, as there would be almost no one awake and lighting up their homes, and virtually no one out driving on the streets.  Perfect conditions!

The mount duly slewed into place; I had aligned on nearby M42 and Pollux so that the mount was pointing pretty accurately.  I would be the first to admit that I may have fooled myself into thinking I saw it, if that were true.  But I don’t think it was.  It was still almost impossible to see.  Almost.  Because there, even dimmer than M78, was a very, very faint little patch.  As I manually slewed the field around, that exceedingly dim patch moved with the field.  Success!

Next time:  Broken Mount and New Observing Chair


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