Comet 21P/Giacobini-Zinner
Comet 21P/Giacobini-Zinner has made a grand tour of our summer sky as it approached the perihelion portion of its orbit. In September, as it passed closest to both Earth and the Sun, it has been “posing” with other deep sky targets.
I took advantage of one of our rare clear nights – September 16th – to catch the comet in these colorful tableaux. The green comet – only 1.2 miles in diameter – is approaching the star Eta Gemini, or Propus, which shows reddish orange.
To the left (East ) the brighter portion of the Jellyfish Nebula (IC3443) glows bright red. To the north and west lies M35, an open cluster with baby blue stars, and its companion smaller cluster NGC 2158 with a distinctive golden glow. For the second image I repositioned his scope, leaving M35 behind but adding the bright red Monkey Head Nebula to the southwest.
“The distinctive colors are a bonus of long exposure photography, not a trick or artifact of image processing, and they are associated with specific attributes of these celestial objects: Comets glow green from cyanide and other carbon forms; the red nebulae are principally ionized hydrogen gas, and the blue and gold stars in the clusters speak to the age, type, and velocity of the stars – the blues get a blue Doppler shift because they’re moving towards us!”
I shot these from my Yonkers backyard through a Borg 55FL astrograph with an IDAS LPS-D2 filter on a ZWO ASI1600MC cooled astro cam, tracking with an iOptron CubePro 8200 mount. Four second exposures were used throughout, accumulated into 3 minute stacks via SharpCap, and processed with PixInsight (PI). These images used the Comet Alignment utility in PI to create a “comet only” image freezing the comet’s movement, and a background image to combine with the comet.
