Sunday evening 19 July 2020 the skies cleared providing another viewing opportunity for C/2020 F3 (NEOWISE). We went just outside our garage door and looked northwest below the Big Dipper. A large River Birch tree shades us from the glare of the nearby streetlamp. We first looked at the comet through our 30x telescope.
I then set my digital camera on the tripod and zoomed all the way in for a photo. It was 9:53 pm local time. Several features are labeled in the resulting photograph. Comets have a core nucleus composed of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. Some describe them as freeze dried dirty snowballs. Their surface is littered with a thick layer of very dark material. The Sun heats this dark material and causes the ices to vaporize and escape into a cloud of gas around the core called a coma. The pressure of the solar wind forces the gas to stream away from the Sun producing the comet tail. It is very faint extending upward in this photograph. The Sun is out of view far below the bottom of this photo frame. Two reference stars were in view shining through the thin comet tail and coma.
During the next 15 minutes, I experimented with different camera and zoom settings with varying success. In the last few photos, I noticed the two reference stars were not in the same places as before. Comets are in orbit around the Sun and thus moving quite fast. I was seeing the result of this rapid motion.
I selected three photos taken at 9:53 and 9:56 and 10:07 pm. All were at ISO 3200 and the same full zoom. Using Photoshop Elements, I superimposed them with the reference stars aligned. It was easy to see the movement of the comet core in that short 14 minute interval.
I was very pleased to see that unexpected result. Before quitting, I turned in the opposite direction facing southeast. Jupiter and Saturn had risen and were watching over my shoulder as I paid attention to NEOWISE. When a planet is at opposition, it is opposite the direction of the Sun from our viewpoint of Earth. They deserved to be photographed. Here they are at the same scale. Jupiter’s four Galilean Moons are spread across the frame. Saturn’s Rings even showed tiny gaps between them and the planet. It was a fitting end to a beautiful night.