Imaging the Elusive Comet 46P/Wirtanen From the East Cost
Comet 46P/Wirtanen is making a swing through the inner solar system and AAA Astrophotographers were out trying their best to photograph the faint orb. It began to show up in photos as more than a green dot in mid-November to those with large telescopes. While advertised as about magnitude 5 or less, the diffuse comet wasn’t really visible to the naked eye.
Mauri Rosenthal led off with this post on the Astrophotography Google Groups:
“Ok, here’s how this all played out:
- We had a lot of rotten weather, or evening commitments, between Dec 1st and today.
- I managed to try out my 135mm lens on Dec 4th and got a nice shot of Pleiades (M45) with cute star shaped stars https://www.instagram.com/p/Bq_vp0RB5fZ/ . This is a fairly tight crop just to show off the fun stars; I think this effect would have been nice with the comet when the comet was close. The comet was not well positioned on that night for me.
- On Dec 10th I had my best shot at the comet; I used my best wide-field optics (Borg 55FL astrograph, same as my Highline rig) and got a couple of hours of the comet passing against a generic background in Cetus. I posted this movie https://www.instagram.com/p/BrUaqd7hOKJ/ which came out pretty well given the even background that night (no moon no clouds). I showed the still version of this at the meetup last week.
- The weather was foul on Dec 16th, described below for the comet’s proximity to M45. There are nice shots online from Japan and similar places far from here of the comet near Pleiades.
- The weather was better on the 18th and 19th (last night) but the moon has been brilliant. For the first time I attached my nice Canon zoom (17-55 f/2.8) to my ZWO astrocam and it gives decent stars as long as you ignore the coma in the corners. It gave me exactly the field of view (FOV) I wanted, though, to get the comet, M45, and California Nebula. Unfortunately I had wicked banding on the 18th; I spent some time trying to minimize it; clouds rolled in, and eventually I decided I needed to shoot at the comet when I could and just deal with it. I reluctantly posted this yesterday https://www.instagram.com/p/BrltMTlBrRq/ after I crushed the contrast to make it look interesting on a phone. In real life it’s a noisy mess, but people like it! What the heck.
- Last night (Dec. 19) we finally had very clear skies but the moon at 90% was a total pain. While I could have done a very wide shot to again incorporate the comet plus M45 and the California Nebula, I decided to forget about M45. I tried a different USB cable and I think this resolved the banding problem, but with the moonlight and no flats the subs are very messy with a big purple ring around the center. I’ve got about 3 hours of 3 minute subs (actually livestacks of 23 X 8 second exposures) so I have a lot of decent data, but with the nebula and the gradients comet processing is very challenging. So the comet subtraction step, for example, used in the 12/10 image (comet against a boring even background) just creates a hideous mess with last night’s images. Hence I’ve given up on fancy processing and just used the best hour of data. The comet smudges during this time but not too badly at the focal length I used. There’s no banding but I still used a lot of curves adjustments to hype the two objects and minimize the bright splotches from the gradient. Pretend you’re viewing this on a phone:
Instagram post: https://www.instagram.com/p/BrpOrMJh-Am/
- Technical data:
- Canon 17-55 mm f/2.8 zoom lens at approximately 50mm
- IDAS LPS-V4 Filter
- ZWO ASI 1600MC camera
- iOptron CubePro 8200 mount unguided
- Exposures- see text above
At this focal length no fancy comet processing was needed. Processed with PixInsight, mostly just stacking and exposure adjustments with final crop and contrast adjustment in Instagram on my phone.
Gowrishankar L. was probably the first from the group to get a good photo on Dec. 8 from Jenny Jump State Park in New Jersey:
“A single exposure shot of the approaching comet 46P/Wirtanen shot at 400mm FL. At this FL the movement of comet was very apparent, however I wasn’t able to capture the complete sequence as I felt completely incapacitated by the brutal weather (24F) & me stumbling with Backyard EOS which ran into all sorts of problem. This will probably be my best shot of 46P unless the weather becomes favorable next Saturday. The comet is still very faint and it needs a suburban sky at least. Check your local weather and make sure to head to dark sky place to image and see this comet next weekend (Dec 15-16) as it will be close to M45! Thanks to @charotarguy for the counter-weight without which this image would’ve never been captured in first place, thanks to @helicopterjeff for organizing the meetup & providing the nearest NGC and Thanks Adam @spacedoutpics for confirming the comet capture and wonderful gesture for getting us hot coffee and motivation to sustain the cold and keep going. https://www.instagram.com/p/BrLU5z5hAM-/
- EXIF: 1 shot @ 400mm
- ISO 3200, F5.6, 120 sec
- Canon 5D Mark III Astro-Modded
- Canon EF 100-400mm F4.5-F5.6 L Lens
- iOptron CEM60 Center Balanced German Equatorial Mount
- Photoshop CC Curves, WB adjustment”
John Bills planned an excursion to nearby Anthony Wayne Recreation Area in Harriman State Park, site of occasional AAA observing, in the early hours of Dec. 19, one of the few very clear nights available. Chirag Upreti and I accompanied him and we arrived about 2:30 am to the parking lot and set up in anticipation of the moon set at 3:30 am.
From John’s Instagram post:
“Crisp cool early morning capture of Comet 46P/Wirtanen just after moonset around 330am. Good times with @stanhonda and @tinchu_chi at Harriman State Park just 1 hour north of NYC. Here is a series of single frames to show how much the comet moved relative to the stars in just a couple of hours. Canon 200mm with 2x extender on a tracker. 46P hangs out mostly around Jupiter and its heavy content of cyanogen when turned to gas as it nears the sun, and us, ionizes by ultraviolet light from the sun. That gas cloud glow is from over 7 million miles away and is about the size of the full moon in the sky.
https://www.instagram.com/p/Brl6Wrchqqm/
- Canon 77D
- Canon 200mm f2.8 II with 2x TeleExtender
- 20” @f5.6 ISO 1600
- tracked on iOptron SkyTracker Pro
- processed on iPhone in Photos and SlideLab”
A second post used the zoom feature in iMovie:
“Crisp cool early morning capture of Comet 46P/Wirtanen just after moonset around 330am. Good times with @stanhonda and @tinchu_chi at Harriman State Park just 1 hour north of NYC. A single frame from a Canon 200mm with 2x extender – zoomed in Ken Burns style to show the greenish glow. 46P hangs out mostly around Jupiter and its heavy content of cyanogen when turned to gas as it nears the sun, and us, ionizes by ultraviolet light from the sun. That glow is from over 7 million miles away and is about the size of the full moon in the sky.
https://www.instagram.com/p/Brl3hJMBo-9/
- Canon 77D
- Canon 200mm f2.8 II with 2x TeleExtender
- 20” @f5.6 ISO 1600
- tracked on iOptron SkyTracker Pro
- processed on iPhone in Photos and iMovie”
Chirag reported in email his efforts:
“This is the image I got from the 200mm stack. ~20 minutes of stacking, 50sec each, ISO 3200, f/5.6 (70-200 f/2.8), slight crop in. Stacked in nebulosity. The comet moves noticeably, so I made two stack one for the stars and one for the comet and then blend them together.
Thoughts welcome and thanks you Stan for the invite and John for the drive, much fun!
California Nebula must have been low on the horizon, since I was avoiding the tree line and centered the comet in the frame. Maybe it’s in the 70mm shots I took earlier.”
Even with John’s image stabilized binoculars, the comet was a faint gray fuzzy object. In photographs it did show up greenish, which made finding and composing somewhat simple. After shooting some of it floating among the stars, I framed it with a nearby tree in this single frame shot.
https://www.instagram.com/p/BrlI4fcgbgV/
- Nikon D850
- 70-200mm lens at 200mm
- ISO 10,000, 6 seconds, f4
- iOptron SkyTracker Pro
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