Comet C/2022 E3 (ZTF) was discovered on March 2, 2022 by the Zwicky Transient Facility (ZTF), located at Mt. Palomar in southern California. Since it was the 3rd one discovered in the fifth half-month E (i.e. A, B, C, D, E) of the year, it is named 2022 E3 ZTF. The inbound trajectory from the Oort cloud to the Sun of this long period comet was 50,000 years. However, the outbound trajectory suggests at best it will not be back for millions of years, or it may be ejected totally ejected from the solar system, never to return—time will tell…

The green color is due to diatomic carbon (C2) produced by the photolysis of organic molecules that evaporate from the nucleus (note, watch for the error, while CN emission is strong from this comet, the green color is not due to CN which actually emits mainly in the violet). The Sun’s UV radiation excites C2 which then emits green light at 518 nm. The excited organic molecules however are not stable in the UV radiation and thus they degrade within a few days. For this reason, the green emission is always close to the nucleus, it does not survive long enough to get out into  the tail. 

Capture and Processing
This image was taken from January 31st 11.32 PM to 1.37 AM on February 1st at closest approach to Earth, 42.5 million km. A total of 215 exposures of 30 seconds each were taken over 2 hours, each image separated by about 3 minutes. 

Images were taken using an L-eNhance HO filter, as my Bortle 8 light pollution is especially bad lower to the north, with a streetlight and a brightly lit neighbor, so white light images were totally washed out. Fortunately, the OIII bandpass of this filter covers the major Swan band for C2 green emission, so captures most of the lovely green color. There also is some red glow from dust visible in the red channel, and perhaps just a trace of the ion tail pointing toward the lower left of the image.

In DeepSkyStacker, two average comet stacks were done, alternating frames in each of the stacks to produce an aligned comet with clearly defined stars as they moved relative to the comet.  The stacks were each processed identically in StarTools. Then in Photoshop, StarXterminator was used to remove all the stars from each of the stacks. The two comet stacks were then averaged. The stars were added back in using linear dodge (add), showing them as as they were at 11.37 PM . Final color adjustments were done to both layers, as well as noise reduction with NoiseXterminator.