Wednesday, December 25, 2013

Post-solstice KPNO sunset

The previous post detailed an annual trip to photograph the Sun setting behind Kitt Peak National Observatory as seen from the Catalina Highway.  As this alignment occurs 3 days prior to the Winter solstice (while the Sun is trekking southward), there is a second opportunity to observe the alignment approximately 3 days following solstice as the Sun is once again passing the same point on the horizon (while trekking northward).

Approximately 10 folks came out yesterday to take pictures of the Kitt Peak ridge line and observatories silhouetted by the Sun. Once again, I was taking pictures of the Sun using my Canon T2i through my Stellarvue 90mm triplet refractor with a Lunt Solar Systems Herschel Prism and a 2x Barlow lens.  This results in a focal ratio of approximately f/14.  Overall, the atmosphere was far less stable than the attempt last week which made focusing quite difficult.  At left is an image of the Sun about 20 minutes prior to sunset.  You can see there are some very nice spots on the disc and compared to the later images below how quickly the seeing (atmospheric stability) would continue to deteriorate.

As last time, here are two images of the Sun as it set behind the National Observatory.  The building that is on the left of the ridge line that appears as a "7" on its side, is the McMath-Pierce Solar Telescope.  At far right on the summit is the Mayall 4-meter Telescope.  Click the images to enlarge them to full size.

In addition to the generally poor seeing there was a thick inversion layer that was forming in the valley as temperatures quickly dropped around sunset.  It was easy to see this layer from our vantage point as it developed.  This resulted in a large amount of atmospheric dispersion and some amazing colors of the final bits of the setting Sun.  Below is an image of the nearly set Sun which shows the green rim as well as some blue-

Finally, here is an image at full resolution of the camera of the last fraction of a second of sunset-  The atmospheric dispersion shows colors from orange/yellow at the bottom to blue at the top!  None of this was visible to the eye, as expected, but I was surprised to see this amount of color in the image-  It is not much to look at due to the lack of context in the picture, however, knowing this is the Sun makes it impressive (to me anyway!)

Happy holidays!

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