Comet 21P Giacobini-Zinner is continuing its remarkable trek along the Milky Way. The comet is past perihelion now and moving further from the both the Sun and Earth.
Over the coming weeks the comet will follow the Milky Way south. From Gemini, through Monoceros (east of Orion) and towards Sirius in Canis Major. Here finder chart for the comet during September and October.
The Milky Way in this part of the sky is dotted with open clusters and bright emission nebulae so there are interesting photographic opportunities as the comet fades. It will pass close to NGC 2264 (Cone Nebula / Christmas Tree Cluster) on Sep 24. And then Messier 50 on Oct 8.
I was lucky to get clear sky for an encounter between 21P and the cluster Messier 35 in Gemini a little while back:
21P has been a tricky comet to image : long exposures weren’t possible because the comet moved too quickly. My strategy was do shorter exposures (say, 30 seconds) and stack images on the comet (producing star trails) and stack again on the stars (giving a motion blurred comet). The two images could be tidied up and blended in Photoshop. More science than art, but giving nice pictures like the one above. This is all good practice for the forthcoming appearance of Comet Wirtanen in December!