Thursday, December 20, 2018

Comet 46P/Wirtanen

On December 18th, 2018, Comet 46P/Wirtanen was naked eye visible from my backyard.  Just barely.  

If you waited for moonset and knew exactly where to look and used averted vision.  Yup.  There it was.  A dim grayish-green splotch in the sky.

It was even better when looking through binoculars.  It became a dim green blob.

Then, I aimed the 10 inch Dob at it.  It became a much bigger, brighter, but still dim green blob, but now with the increased aperture and magnification, I could see the comet's motion against the starfield.

Using the ZWO ASI294MC imager, I captured this.

46P Zooming by
This data was captured and live stacked with SharpCap.  It's 151 frames at 8 seconds exposure, each.  So, basically, this is a 20 minute exposure with the starfield being tracked so the relative motion of the comet is apparent.

What if I wanted to track the comet instead of the starfield?  It turns out that is a much harder problem.  The scope only has tracking modes for lunar, solar, and sidereal.

This was a perfect time to gather data and give DeepSkyStacker a try! 

With the data, I could use DeepSkyStacker for post processing.

I captured over 500 frames of comet data during this session.  That ate a lot of room on the hard drive. Clearly, it is now time to increase the size of the storage in the astro laptop.  That'll be the subject of a future blog post.

With DeepSkyStacker, I had to mark the comet's position in each one of the data frames.  That was pretty tedious, but afterwards I found that it could be done algorithmically if the frames have an embedded date and time stamp. 

With that done, I started the stacking process.

Hours later, and with some tweaking, this is the best I could do.

46P Zooming by
The stacked brilliance of the comet swamps the resultant image and color is missing, but you can see the streaks of the starfield!

I will continue to use DeepSkyStacker for post processing data throughout the upcoming year.  Who knows what new things I'll learn?



  1. Pretty cool! (and pretty jealous you're on vacation) Enjoy yourself! Merry Christmas to you and Priscilla!

  2. I like both versions of the images. Impressive!

    1. SharpCap's live stacking is amazing. The image forms as the frames arrive from the camera. DeepSkyStacker promises to be another powerful tool, but with a steep learning curve!


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