Solstice Sunset

Last night was the "sunset expedition" - the first time this season that the sun set behind Kitt Peak National Observatory (KPNO). After an announcement on the Tucson Amateur Astronomy Association's forum, there was a little interest in observing it, so the sunset hunt was on! In all we had 8 people and 7 scopes or lenses focused on the sunset.

We met at the McDonald's on Tanque Verde and Catalina Highway at 4pm. Melinda and I were the last to arrive with a few minutes to go, so made the drive up to just short of milepost 9 in short order with less than an hour to sunset. After indicating the spot to the group, we spread out and set up gear, some focusing and aligning on the sun, me - I did a quick focus on the sun then set up and aligned on the profile of KPNO. I was concerned about some thin clouds moving down from the north, but there wasn't much we could do, so we waited.

Time zipped by quickly and seemingly before I knew it, the disk of the sun became visible in the upper corner of the frame. By the time I determined the correct exposure, it had just touched the mountaintop observatory and I started the timer sequence with an exposure every 4 seconds. Bill, our former club president was worried it wouldn't span the mountaintop and announced he was going to move a few yards - but we assured him all was ok and besides, sunset would be over before he would be able to reacquire the image! And then it really was over. The alignment was perfect, everyone got some great images and all were carrying a silly ear to ear grin. And what was interesting, there was actually a group of sunspots visible - the first in a long time. In the shot here it is just above the University of Arizona's 90 inch telescope - second from the right.


I had read a notice online that the moon and planet Mercury would appear in the sky together, so some of tarried a bit while others packed up the the rapidly dropping temperatures. While we waited Melinda and Jennifer compared silly-looking hats.The moon was almost exactly 36 hours old - a skinny crescent that suddenly seemed to appear out of the darkening sky and a surprisingly bright Mercury less than 5 degrees away. A striking sight with the still orange clouds that glowed after the sunset.


We finally ambled to town and a small subgroup of us stopped for some pizza and beer before finally heading home to download images from our cameras. While my focus and the sunset alignment was great, I inadvertently had overexposed my shots very slightly and the red channel was saturated (since the setting sun is mostly red). It does affect the image some, but it is what it is - will just have to do it again and be a little more careful next time. I did make a quick movie of the exposures I took - we couldn't figure out how to display it here on the blog, but our friend and co-observer Tom Polakis agreed to host the .GIF file on his photo site. If your computer connection can tolerate downloading a 5MB file, take a look at the sunset movie. With the clouds moving in front of the sunset, it is quite incredible.


In the next few days the sun moves a little too far south to align with KPNO, but in a week it will be heading north and the alignment will happen again. The next chance is on Friday 25 December (yes, sunset on Christmas Day). It will be a good pass - if the weather is good I know at least one of our group will be doing it again with me...

(Click on the picture to open and view the .gif file. This is a 5MB .gif file, so it is very large!)