A new comet is in our neighborhood passing by at a relatively close 28 million miles from Earth.  It is a very long period comet that we have not seen before, but it has visited the inner solar system over 1300 years ago.  However, nobody noticed it because it was probably too dim to see naked eye.   It was discovered late last year by Japanese astronomer Masayuki Iwamoto.

Below is the Star-Streaks version with minimal processing.   Both images were treated minimally in these first iterations of processing.  There is probably room for improvement, but I doubt I’ll get much more than what I have here.

I shot this from a Bortle Red/White zone in the middle of a metro area.   It was moving so fast that even 30 sec shots showed trailing.   So, I went with ISO 3200 and 30 sec exposures even though it trailed a bit, which was about max for the sky conditions I had this night.  I shot some 1 minute subs while trying to guide on the comet, but my DEC calibration was not working, so they showed some trailing in DEC.  Plus, I was barely able to pick it up with 4 sec subs, so it was not tracking too well at that setting.

These two didn’t come out too bad, I guess.   A darker location would have shown the tail better, probably and there is some hint of it here.  Reports are the comet can be seen in binoculars from dark sites, which is pretty good for any comet.   But, I knew from experience that when they are barely visible in binos from dark sites, binoculars are almost useless from inside a metro area, so I didn’t even try.

So far, I’ve managed to image Comet 46P/Wirtanen four times during this apparition with my TV-85 scope and twice with camera lenses.  For this time of the year, that is pretty good.   December and January are usually months of unending rain and clouds down here in Cajun Country.

Now that the main part of Comet Wirtanen’s visit is over, it is a good time to do a roundup of the data and see the bigger picture.   So, I took the best four star-freeze versions from those four times with the telescope and combined them into one display image above.    That way, you can easily compare the shape of the comet and see how it changed depending on our angle of view at the time.

The dust and ion tails were both mostly hidden behind the huge coma on this comet.  It was huge because it was so close to us.   But, since it was still further from the Sun than we are and the Sun, Earth and comet were in a line, the tails were pointing directly away from us.   That foreshortens the length of the tail and makes it look like it doesn’t even have one at times.   It is just the geometry of the view angle and the way the coma can overwhelm the dim tails when they are behind it from our vantage point.

When we were more at an angle to the Sun-comet angle, the tail appeared longer.   When we were in-line with it and the Sun, the tail decreased.   So, it is not totally comet activity at this point that controls tail length, it is view angle and how much is behind a thick coma.   You still have the solar wind and how chaotic it is that causes the tail to “flap” like a flag when the wind varies.  But, mostly view angle.

46P came in low going high and crossed our orbit then angled above the elliptic plane heading away from the Sun.  Our view now is from underneath, you would say.   That is why the tail is south now when it was mostly on the north side when it was below the elliptic.

I had been wanting to try imaging 46P with the 200mm telephoto lens I have.   I thought I could bust through the LP with the addition of the Lumicon 72mm Deep Sky filter that fits that lens.  Oh, well… not enough pass-through for the comet wavelengths and blocking of the LP.  It helped, but not enough in the white zone I was shooting from.  It works for H-Alpha nebulae, but not much for other stuff.

After a long spate of cloudy and wet weather, it finally cleared enough for imaging on the night of Jan 4th/5th, 2019.  My last imaging session was just before Christmas, so it had been a while.

The imaging went reasonably well, just getting home was a little difficult due to car trouble, but I made it.  Then, I locked myself out the vehicle before I could unload my stuff.  Doh!   Oh, well… $60 bucks later I was busy working on this image (without getting any sleep, either. )    🙂

After doing the above images, i did another take on the star-freeze version with this cropped and more gaudy version  below.  I think it catches more of the extent of the whole comet like the star-streaks version does:

Speaking of the star-streak version, the one I did below is almost pristine.   I barely did anything to it.  It shows the ion tail much better than the first star-freeze versions, too:

Terrible conditions (and location) for this imaging session.  I tried several things before settling on one minute sub-images as my best bet for the conditions.  (Bortle 7/Orange zone, high-altitude jet stream clouds with bad seeing and temps near 60 degrees, which while nice and cool for us, is a bit warm for a Canon sensor inside a camera body. )

What can I say?  At least there was some photogenic aspect with Capella in the image.  Processing was difficult with lots of residual noise from all the LP, clouds and warm temps.  But, it was an opportunity to image.   Late December usually doesn’t offer much in the way of clear night time skies.

After these 1 minute subs, I took a chance and shot 20 x 300 sec images at ISO 100 while tracking the comet with the guider.  I was able to add those in to the above image and I came out with this as a result:

As you can see, the longer subs managed to pull more of the ion tail out of the muck.  I also added some of this to the star-freeze version and updated the display images.

The first shots of the night of Dec 10, 2018 were some 30 second ISO 6400 sub-images of Comet 46P/Wirtanen and the last 4 shots were 5 minute subs at ISO 3200 of the same, but guided on the comet instead of the stars.  I mixed in some 60 sec ISO 6400 and ISO 3200 subs in the middle.  The first image above is a combination of three sets – the 300 sec ISO 3200 subs and all of the ISO 6400 ones.   The second image is just the 30 second ISO 6400 subs alone in a star streaks rendition.

Before I could even start shooting, I had to take the mount apart in the field and unstick a stuck motor that was giving me lots of trouble.  I almost thought I would scratch and not get any shots of this naked eye comet.   Luckily, I had tools and was able to rectify the situation.

I had trouble seeing the comet naked eye at first, but as soon as it rose high enough out of the muck, I was able to spot it without optical aid.  I was at my Bortle 4/Green zone site and it was probably the clearest night so far this season.   So, conditions were exceptional and it was cold enough (down to 37 degrees F) to use ISO 6400 without too much noise.

I still have one other set of 1 minute, ISO 3200 subs left to process.  I’ll probably be updating this post later after I do them.

Edit:

Yep, I was able to get these 40×60 sec ISO 3200 sub-images calibrated and stacked.   Here’s the result of them by themselves:

Not too bad for 1 minute exposures.   Color could have been better.    Oh, well….

For an encore, I have this animated GIF showing the movement of the comet  for just under an hour of time:

While the comet is moving and will blur if you expose too long while tracking the stars, you can also track it and expose for much longer.  I tried 5 minute ISO 3200 sub-images and managed to get 4 like that before I tore down the rig.   Here are two of them together for a total of 10 minutes of exposure:

Finally, here is the set of 40 x 1 minute ISO 6400 sub-images with a little bit of the above data and labels describing the image:

I was surprised at how well ISO 6400 worked out.  Usually, it is too warm to shoot at this setting.   It was 37 F when I got back to my place and shot the darks.   I just left the scope outside and did them while I napped.  It was probably a little warmer when I took these subs, but close enough to calibrate the extra noise out of them.

Here is 64P/Swift-Gehrels, a comet that was near M33 recently.   I missed it then, but I finally caught up with it Saturday night, Dec 1, 2018.

I used 4 minute subs and I could have gone even longer at this location, but my guiding was iffy with bad seeing.   Out of 20 minutes of subs, I lost one, so this is only 16 minutes of exposure.

Since it was so few, I just stacked the subs once while aligned on the stars and then used one sub of the central core to hide the streak  caused by the comet’s movement in the sky.  A quick and dirty star-freeze job.    lol   🙂

Comet Wirtanen is looking to be the best comet this season.  It is a short-period comet that comes around every 5.6 years.  It should be at it’s best as it passes closest to Earth:

• Occurs Dec 16, 2018
• Less than 4 days after perihelion
• The comet is near its brightest

• Geocentric Distance 0.0775 AU
• 30 Lunar distances
• 11.5 million km
• 7.1 million miles

So, it has 2 more weeks until that happens and look at the size of that thing already.   It is huge!  See the comparison with the moon taken with the same scope below:

BTW, the above image appeared on the home page of SpaceWeather.com on Dec 4th and 5th, 2018  and is also featured in an article on the Televue Optics blog, which are the guys that make my scope and focal reducer/flattener.   🙂

I re-vamped the above image with the better version star-freeze image (and also with both the comet and the moon oriented north) and that is here:

I shot two sets of data for this comet.  Both were 40 sub-images.  The first image and the image below are from the first set.  The moon/comet comparison image above was done from the second set.

Taking another crack at processing the first data set, I made this version below that has a slightly different comet position, is a little lighter and shows more coma, but less tail:

Here’s the second set of data with a star streaks and star freeze version of the comet with extra processing plus a red boost on the former and minimal processing for the latter:

Finally, here are both sets of the comet together, but with the background stars from only one set of 40 x 2 min subs:

Lots more coma is visible, plus the tail from the fist set of subs shows as well.  I think here we have a coma that is so bright it is blowing out the faint tail as seen in the second set above.   Not as much coma was picked up when it was lower in the sky muck, but the wavelengths from the tail got through and made it more obvious, as seen in the first set of subs.

So, it is possible that shorter “core” sub-images mixed in with longer exposures to get the coma might be a way to tame this comet and get a good final image with DSLR equipment.   I will try that the next time I get to image this beast.

Edit Dec 23 2018:  Reprocess of 2nd set of 120 sec ISO 3200 shots and added in all other data taken that night.

I just knew there was more there.   I just had to strive for the right stretch and do selective red channel boosting.   The tail was mostly in the red channel and that gets clipped a bit with the removal of LP and background noise.   So, I had to leave as much as possible of the red in the tail area but suppress it everywhere else.  Some selective masks for various saturation and color balance adjustments did the trick.

Edit Dec 27, 2018:

I had a chance to take another crack at the star-streaks version of the image with the above data and considerations and also added Larson Sekanina filtering for the tail: