Friday, August 29, 2014

Another Quick Trip in Search of Dark Skies

Our Summer rainy season is winding down.  Drier air and higher temperatures result as the weather pattern that brings the moisture moves elsewhere.  The result is blue skies through the afternoon, and with the moon still thin, I was tempted to make a run west towards Kitt Peak National Observatory for dark skies.  The program for the night?  Well, checking Heavens-Above, there was a pass of the International Space Station low in the south, passing the conjunction of Mars and Saturn, continuing towards the Milky Way.  That was a good enough excuse for me, so Melinda and I left during the height of rush hour to get up the mountain just before sunset.

Unfortunately, during the ISS pass, the sun was only 10 degrees below the horizon, so the sky was still bright enough that both satellite and Milky Way were barely visible, so am not even going to show it.  Had it happened 15 minutes later it might have been great!  Above is a 4-second test shot a bit before ISS came by - the planets and bright constellations are visible, but it was still too bright for the Milky Way.

Well, since it was a beautiful night and almost dark, what to work on next?  I'm a fan of dark dust clouds that become visible by obscuring more distant clouds of stars, and with the Summer Milky Way high in the sky, a perfect time to image some.  I was enamored of dark cloud complex LDN 673 in Aquila imaged by friend Adam Block with a 32" telescope a couple seasons ago.  You REALLY want to go to that link to check it out!  All the images I saw were of the dark clouds spilling out of the field, so figured it was worth a wide-field shot.  I set up a recently-acquired Astrotrac mount with my XSi and 200mm lens.  I was able to capture 9 frames of 2.5 minutes each, nearly 23 minutes of exposure.  With a moderate crop of the stack, shown at left, the dark complex is barely seen at center, with LDN 684 above it near the upper edge.   There is something to be said for 20 hours of exposure and a 32" telescope for Adam's shot, but a couple hours and longer focal length than my 200 would be an interesting shot too!

While the above shot was exposing, I also broke out another tracking mount, a smaller Polarie on a sturdy tripod.  I installed my "antique" (nearly 10 years old) Canon 20Da camera with a Nikon 135mm lens.  The 20Da works well on emission nebulae, so with the Milky Way still high, I chose to go after an interesting nebula, the Cat's Paw nebula, NGC 6334.  While a small nebula, it sits in an interesting part of the Milky Way.  It is low though, barely over 20 degrees off the horizon at its highest and already was lower than that.  I got 8 frames with the 135mm lens at F/4, combined and shown here (20 minutes of exposure).  The bright stars at left are the "stinger" of Scorpius.  The lower reddish cloud is the Cat's Paw Nebula, the upper red hydrogen cloud is NGC 6357.  There are a plethora of other objects in the field, certainly many dark clouds, so I was happy.  There might be a hint of greenish glow from natural airglow, shooting so near the horizon...

I promised Melinda we wouldn't be out late (she wasn't feeling great), but I really wanted to try to catch a bright comet that was in the evening sky.  Comet Jacques, C/2014 E2 is currently not visible to the naked eye, but is easily spotted in binoculars.  It is moving quite quickly though - its motion was visible even in binoculars over the period of 15 minutes!  While the color was not seen in binoculars, even a short exposure shows the green color of dissociated carbon molecules of the coma.  This is a 3-frame stack, barely 7 minutes total exposure centered on the comet.  There is a barely-imagined straight ion tail going off to the upper right.  There is a blurred red nebula at right center as well, I believe it is Sharpless 2-155, the Cave Nebula.  It looks pretty bright and would likely make a good future telescopic target.  Comet Jacques is getting further from the sun, but closer to the earth - it will stay just below naked-eye brightness, but should be visible for the next couple months...

Even with all the observing we got in, we were home a few minutes after 11pm, not bad for a school night!

No comments: