A Great Alignment and Spectacular Sunset!

Last evening was our first opportunity this year

to observe the sunset alignment of Kitt Peak National Observatory.  About 4 or 5 days before and after the Winter Solstice, it can be observed from a broad pullout on the outside of a curve just below milepost 9.  There is an unimpeded view of the Observatory to the SSW, and though sometimes the cars passing on the road are pesky, it is a safe place to observe the alignment.  It seems a tradition leading up to the holiday season to observe or shoot it and it would seem strange not to chase it - any excuse to get out and observe!  While it can be quite cold here in December above 5,000 feet elevation, yesterday we set a high temperature record of 83F in Tucson, so it was comfortable in long sleeves even without a jacket...

I always have fun trying new imaging options every year, and there was no exception this year.  Our friend Roger, a telescope maker of some renown, built a 5.75" F/8 diameter triplet apochromat a few years back, and I talked him into joining us, and running Melinda's T1i on it.  The 1170mm focal length was perfect for the sun's diameter on the APS sensor.  I quickly adapted his mounting plate to a massive tripod I've had for decades, and the combination was quite robust.  The pictures were taken shortly after we arrived with the sun still a good 10 degrees off the horizon.  Yes, we had some thin clouds, but perfectly clear skies usually make for boring sunsets!

We had a few friends joining us this year from the Tucson Amateur Astronomy Association (TAAA).  Alan Strauss,director of the Mount Lemmon Sky Center, joined us with some small scopes, one for white light and another for H-alpha viewing.  In the image at left, Alan is standing at right talking to Roger, behind his blue telescope, with Melinda sitting in the back of the van.  Jim Miller and his wife Elaine also joined us, setting up his 10" telescope - the picture at right shows him focusing for the sunset.

Jim O'Connor and wife Susan also came along, Jim attempting to take video of the event with laptop and Imaging Source camera (shown at left image).  We all arrived in plenty of time to get our equipment setup, and had a chance to socialize a bit before the sun hit the horizon.  We even had a couple of normally speeding cars stop and ask what was going on...  The picture at right shows the wide-angle view with the spare camera once the button was pushed and pics came crashing in...

Our observing setup is shown in a little more detail at left.  Roger's APO is the blue scope at left.  It has an older Thousand Oakes glass solar filter - a type 2 filter designed for imaging with short exposures.  Not entirely safe for visual observing (a little too bright), but perfect for shooting a dimmed sun on the horizon!  You can also see the kludged saddle plate mount atop my binocular mount to hold the telescope...  We also observed the sunset visually with a C5 telescope with Mylar filter and roof prism diagonal to give a correctly oriented view.  Through trial and error, I found I could shoot a full-size jpeg every 2 seconds with Melinda's T1i without problems, so that is how I shot it.  While the images were quite sharp when we set up, the seeing got quite mediocre a little before sunset.  I'm thinking it was the inversion layer that was very near the level of Kitt Peak, Roger thought it was cooling air falling down the slopes of the mountain we were on.  Effects of the seeing can be readily seen in the time-lapse below...

As soon as the sun entered the field of view, I
checked the exposure to make sure it wouldn't be overexposed, then started the exposure-every-2-second sequence.  Running manually, each was about a 2000th of a second.  As soon as the sun set below the mountain, I switched it to aperture priority automatic, and even through the solar filter, an adequate exposure was about a 16th of a second.  The image at left shows the sun perfectly centered on the Observatory outline.  Yes, the clouds made the pictures a little more interesting, and fortunately, there was a clear zone at the level of the telescope domes above Kitt Peak.  The sun always seems to move a surprising amount from left to right as it sets (because we're in the northern hemisphere).  It also seems to happen so quickly through a telescope, but takes about 2 minutes, telescope or not!  The last piece of sun set between the 4-meter telescope at right and the Steward Observatory scopes to the sun's left, the last bit bifurcated by the flat-topped dome of the 90".

Of course, we get some spectacular sunsets in
Arizona - something about the clarity of the air and the normally clear skies of the drier, more desolate desert to the west.  And did we have a spectacular sunset.  While normally the show is over once the sun sets, it just got more and more spectacular for the next 10 minutes!  While some of the first color shows up in the wide shot above while the sun was still above the horizon, a few minutes later with the sun illuminating the underside of the clouds, they just glowed...  I took a couple different styles of images - at left is an HDR (High Dynamic Range) which combines 3 exposures of different lengths to preserve details in both shadows and highlights of the image.  I wanted to preserve the purple illumination of the front side of the mountains, as well as the bright colors in the clouds.  At right is a 4-frame mosaic with my zoom's maximum 200mm focal length to preserve details of our view to the west from Thimble Peak at right to the south past Kitt Peak.  Of course, I'm limited to the 1600 pixel wide frame here, but it is a good representation of the spectacular sky.  I'm sure you might think that I've photoshopped in the colors, but check out Alan Strauss' post of the sunset and you will see that I'm not pulling your leg!

So finally, the 173 images collected, of both the sun setting and a minute of twilight skies afterwards, were assembled into a movie using Windows Moviemaker, then uploaded to Youtube.  It makes a very nice 30 second sunset time lapse, showing not only the motion of the sun, but also the slight motion of the clouds past the mountaintop.  You should be able to play the movie right here in the blog post, or you can hit the youtube icon at the bottom of the viewer to go to that site for viewing.  Enjoy!