Comets C/2017 T2 (PanSTARRS)
There are dozens of comets moving around the solar system but most are too faint to be of interest to amateur astronomers. Of those bright enough to be within range of amateurs in 2020, two are of particular interest:
- C/2017 T2 (PanSTARRS) is very well placed throughout the first half of the year high in the northern sky.
- 29P/Schwassmann-Wachmann is a very different type of comet. It shows frequent outbursts and is well worth monitoring.
C/2017 T2 (PanSTARRS)
Discovered in October 2017 when over 9 AU distant from the Sun, it was thought that this comet could become really bright. Unfortunately, that did not happen, but it is still a nice object for imaging, and is very well placed for observers in the northern hemisphere in early 2020. At the start of the year, the comet is high up in northern Perseus heading towards the Double Cluster on 26-27 January. From there, it starts to loop back and head towards Ursa Major, reaching perihelion on 04 May at a distance of 1.6 AU from the Sun and 1.7 AU from the Earth. (At perihelion, the comet is predicted to be almost 10 times brighter than it appears in figure 2 below.) Three weeks later, on 24 May, it encounters M81 and M82. Figure 1 shows a screen shot from the Guide 7.0 planetarium program showing the position of the comet in relation to the galaxies on 24 May. The circle is 3° in diameter.
The comet then moves south during June, July and August before becoming too low in the sky to view. Reference  provides its orbital elements and a map of its path.
Figure 2 shows the first image by Mike Harlow of the comet, taken on 29 November 2019 when it was just 3° west of Capella in Auriga. The image includes a foreground Apollo asteroid, number 99248, which just happened to be passing at the time! Field of view 16x16 arcmins for each pane. 30.5 cm f/3.6 astrograph, 47 x 30 s exposures with CCD and luminance filter.
In early December 2019, C/2017 T2 was at an altitude of approximately 85° at midnight, well-placed for observing. Nigel Evans attempted to image the object on 06 December, using a Celestron EdgeHD 200 mm Schmidt-Cassegrain telescope with SBIG 8300 camera and LPF, 2x2 binning. After hiding indoors from the cold weather for an hour while the telescope dutifully recorded the comet, he checked how it was going and was horrified to find that all the stellar images appeared as doughnuts! With the telescope pointed up so high, the camera had slowly slid out of the eyepiece holder by about 3 mm and only the first two images were sufficiently in focus to stack into the final image, presented as figure 3 below.
Fig. 1. Position of C/2017 T2 on 24 May 2020.
Fig. 2. Comet 2017 T2 (PanSTARRS), 29 November 2019, Mike Harlow.
Fig. 3. Comet 2017 T2 (PanSTARRS), 06 December 2019, Nigel Evans.
The comet is unusual in that its orbit is only slightly elliptical. With a period of 14.8 years it is always further from the Sun than Jupiter and, as a result, is usually faint, near magnitude 14. However, it undergoes frequent outbursts during which it can brighten significantly to nearer magnitude 10. I imaged it during 2008, and the images show the typical, almost circular, form of the coma, and a bright nucleus. Gradually, the comet moved into the southern sky out of range of my telescope. Now it has moved north again and is currently in Pisces, just 4.5° south-east of gamma Pegasi, so is well placed in the south for observation as darkness falls. The comet will be well placed for northern hemisphere observers for many years. Again, reference  has maps of its track (from 2012 to 2027) and orbital elements for planetarium programs.
Richard Miles of the BAA has studied 29P extensively over many years and regularly takes images with the Las Cumbres Observatory (LCO) network . All images from the network are freely available to download and process as long as LCO is credited if the results are used in any publications.
Jonathan Shanklin has written an article in the December 2019 JBAA  providing a summary of comets, visible in 2020, of interest to amateurs. The article also shows a nice sequence of images by Damian Peach of 29P in outburst.