Sunday night, December 16th, was the evening of the closest approach of Comet 46P/Wirtanen. The comet was close enough and bright enough with an apparent magnitude between 4.0 and 4.5 that you could see it with the naked eye if you had good, dark skies. Thankfully, that’s just what I have living out in rural Missouri, and we also had crystal clear skies. The comet can be seen between the Pleiades Cluster and Taurus through Wednesday, but as the Moon’s phase transitions from 1st Quarter to Waxing Gibbous, dim objects in the sky will be harder and harder to see. Throughout this coming week, the best time to view the comet will actually be in the very early morning after moonset. You can check out more about where to find and when to view the comet at Sky and Telescope, https://www.skyandtelescope.com/astronomy-news/observing-news/comet-46p-wirtanen-and-moon/.
The image below of Comet 46P/Wirtanen is the result of stacking 63 exposures each with a shutter speed of 20-seconds, ISO 6400, aperture f/8, and a focal length of 200 mm on a Nikon D500 through a Tamron 70-200mm f2.8 riding atop a Celestron 8″ SCT. The telescope was there just to provide the clock drive so that the camera moved with the stars’ diurnal motion. Each raw image file was corrected for dark current, bias current, and the response across the frame was normalized using a flat field image. I’ll write up a tutorial on how to collect these images and why they’re necessary later. The images were then aligned and stacked on the comet, which is why the stars appear as streaks. Since the comet is moving quite rapidly past us, its motion relative to the distant background stars is very noticeable, even in the short timespan of this image set.
You may have noticed the very green color to many of the images of Comet 46P/Wirtanen, including this one. The green color is not a image processing artifact, but is indicative of the comet’s composition. Most comets contain a enough cyanogen (CN) and diatomic carbon (C2). As a comet approaches the Sun and its surface warms, volatile materials such as cyanogen, water, and others begin to vaporize forming the comet’s coma and tail. When cyanogen and diatomic carbon interact with the Sun’s ultraviolet light and fluoresce to create the characteristic greenish glow of many comets.
We were at Cocoa Beach for three nights where during the day we interacted with visitors to the Kennedy Space Center where we had a large display assembled sharing information about the mission, its objectives, and its importance to improving our understanding of space weather. As invited guests, we were given the opportunity to witness the launch from the same grandstands in which the families of the Apollo astronauts watched their husbands, brothers, and sons blast off on their epic voyage to the Moon. It was an awe-inspiring, thrilling, and ultimately frustrating experience.
The launch window opened at 0430 which meant that we needed to arrive at Kennedy by 0030 to meet the shuttle busses that would take us to the viewing stands. Once at the viewing location, we had a magnificent view of our launch vehicle standing on its pad and illuminated by the brightest lights you can imagine. The atmosphere at the viewing site was thick with tension, anticipation, and mosquitoes. Lots of mosquitoes! During the long countdown, several speakers gave talks about the mission, which we all knew about already, and details about the launch sequence and timeline, which many of us did not know. What was truly special is that Maj. Gen. Charles Frank Bolden, Jr., Director of NASA, came out to address us and witness the launch with us.
At 0400, we reached the T-4 minute hold. This was a preplanned hold during which final checks on the launch vehicle, the two Van Allen Probes spacecraft, and the launch conditions were made. Talk about tense and exciting! Movies always make the launch readiness poll sound over dramatic and you come away thinking, “Surely it’s not really that tense.” Yes it is; it really is. As each system was called out, the person responsible for that system would call out either “Go!” or “Go, Flight!” I get goosebumps even now just thinking about that moment.
The evening ended brilliantly. Professor Hanna and I made our way down to a region where my good friend and fellow photographer, Bash Beard, took me when I was in town for the AGU Fall Meeting, Beldon Place. At first, it just looks like a sketchy back alley, but when you peek around the corner, it’s lined with one amazing restaurant after another with just about every type of food you can think to eat. We tried the last restaurant at the end of the alley, Brindisi Cucina Di Mare. Of course I was going to sniff out a seafood joint. What else did you expect?