Learn how to chase away the Moon to keep Comet 46P/Wirtanen in a dark sky. Here's an update on the comet's progress and what to look for in the coming nights. 

Big, bright Moons are comet killers. Those of you seeking Comet 46P/Wirtanen, now a naked-eye sight from rural areas, have probably noticed the waxing Moon creeping up in the comet's direction the past few nights. Some comets are compact and bright and do OK in moonlight, but 46P is large and diffuse and best seen in a dark sky.

Comet at Christmas
This map tracks Comet 46P/Wirtanen nightly through December 25th. While the spots marked here show its position at 8 p.m. Central Time, it will be close to the same position if you observe it earlier or later that night. The comet is brightest when near the familiar Pleiades and Hyades, making it easier to find.
Stellarium with additions by the author

I've prepared a fresh map to help you follow our fuzzy friend through Christmas and a list showing when the comet will be visible in a dark, moonless sky. These times will vary somewhat depending on your location, so use them as guidelines. Check the moonrise and moonset calculator to find out exactly when the Moon sets where you live. As it gains on the comet each night, you'll need to stay up later and later for moonset and dark skies.

Naked eye trio
Comet 46P/Wirtanen (lower right) aims for the Hyades and Pleiades on December 10th. At the time, the comet was easy to see  with direct vision under Bortle 3 rural skies as a soft, 4th-magnitude glow. The comet passed perihelion on December 12th. This shot was captured with a 35-mm lens at f/2.8, ISO 800, and a single 80-second exposure on a tracking mount
Bob King

The best times to see 46P/Wirtanen under moonless skies:

  • Friday, December 14th — Moon at first quarter phase and sets 11:30 to midnight. Some light but still not a comet-quencher.
  • Saturday, December 15th — Moon sets 12:30–1 a.m. Sunday morning.
  • Sunday, December 16th — Moon sets 1:30–2 a.m. Monday morning. Moon getting bright now.
  • Monday, December 17th — Moon sets 2:30–3 a.m Tuesday morning.
  • Tuesday, December 18th — Moon sets 4 a.m. Wednesday morning.
  • Wednesday, December 19th — Probably the final moonless night for diehard observers. Moon sets around 5 a.m., with the comet low in the northwestern sky.

Comet 46P/Wirtanen swoops closest to Earth on Sunday, December16th, and then passes about 1° from bright Capella in Auriga in the wee hours of December 23rd. When closest for several nights around the 16th, the comet will be moving at more 4° per day, or 11 arc minutes an hour, fast enough to notice its motion through a telescope in a matter of minutes. After a full-Moon hiatus, dark skies return to the early evening hours starting December 24th at which time the comet will have faded about half a magnitude. The object is expected to remain brighter than 6th magnitude through mid-January.

Two tails?
A careful look at this narrow-field image of the comet taken on December 8th shows the start of the short ion tail sticking out to the right and below the nuclear region and a vague, tail-like structure perpendicular to it to the southwest.
Joseph Brimacombe

Visually, 46P glows around magnitude 4.0–4.5 with a diameter of nearly a degree. Binoculars easily show the hazy outer coma and more compact, bright inner coma. Through a telescope of about 8-inches or larger, its exotic blue-green color from carbon emission is obvious.

Cooking a nucleus
This sketch of the comet's inner coma on December 11th UT shows the features described in the text.
Bob King

I've drilled down into the nucleus in my 15-inch with a magnification of 357× hoping to discern small fans of denser material emitted by the nucleus. With patience and averted vision I could make out a V-shaped structure either side of the false nucleus consisting of beginning of the ion tail pointing northeast and a short, diffuse ray perpendicular to it, pointing southeast. Both are subtle and captured well in Joseph Brimacombe's photo, above.

Comet's twisted ways
Watch as the solar wind wiggles and twists the comet's delicate tail in this time lapse made on December 3, 2018.
Gerald Rhemann

Photos reveal small fans and other structures that might be possible to see visually on a night of good seeing through larger instruments. I encourage you to work the inner coma with high magnification and share what you see via the comments section. Even in moonlight, you can make gainful observations of this bright region.

While it's always exciting for long-time comet observers to see any comet with the naked eye, the average person probably won't be visually impressed by this fuzzball. It doesn't show a tail — except a short stub in a telescope — and essentially appears as a soft, diffuse glow. One might compare it to a painting done in minimalist style versus a Van Gogh or a da Vinci. As so often happens in astronomy, it's what you bring to the object that helps in appreciating it.

Knowing you're witnessing a rare, close flyby of a kilometer-wide spinning ball of dusty ice that originally formed in the outer part of the solar protoplanetary disk 4.6 billion years ago just might raise the hairs on your back.

Comments


Image of Dave Mitsky

Dave Mitsky

December 14, 2018 at 2:35 pm

I've observed Comet 46P/Wirtanen on several occasions from two different locations (the Blue Mountain Vista Observatory and the Naylor Observatory) using my 8x42 and 12x50 binoculars, two 15x70 binoculars (one of which I own), two different 80mm Orion ShortTube 80 refractors (one of which I own), a 105mm Edmund Scientific Astroscan, an 8" Hardin Dob, my 10" Sky-Watcher Collapsible Dob, a 12.5" Teeter's Telescopes Journey Dob, a 12.5" Cave Astrola equatorial Newtonian, and an 18" StarStructure Dob.

A central condensation was evident at 210x through the 18" Dob.

On Tuesday night from the brighter orange-zone Naylor Observatory, I may have been able to see the comet naked-eye.

You must be logged in to post a comment.

Image of Rod

Rod

December 14, 2018 at 2:50 pm

Dave-Mitsky, that is quite a list. I have enjoyed some views of 46P/Wirtanen this December using 10x50 binoculars, 90-mm refractor (alt-az mount) with 1.25 inch eyepieces and barlow lenses, and my 10-inch Newtonian. The comet on 16-Dec passing by the Pleiades in Taurus, where I live looks like rain starting tonight through Sunday. Hope you can get a good view. If you do, post a note, thanks.

You must be logged in to post a comment.

Image of Bob King

Bob King

December 14, 2018 at 5:54 pm

Thanks for your note, Dave. It sounds like you've brought everything to bear on this comet!

You must be logged in to post a comment.

Image of BadyRenee61

BadyRenee61

December 16, 2018 at 9:59 pm

I seen for the first time Dec. 13 naked eye from my backyard and it.sent me looking for answers here. I have no special equipment.

You must be logged in to post a comment.

Image of Tom-Reiland

Tom-Reiland

December 15, 2018 at 4:25 am

Wednesday and Thursday nights were the first observable nights here in Western Pa in several nights, though Thursday night was the best. I was able to locate Comet Wirtanen through my 10 X 50 binocs between 8:30 and 9 PM while the Moon was still up. It wasn't easy and it looked like a round smudge in the area f Western Taurus. I went inside to wait for Moonset and take a nap. I turned off all my lights and placed my binoculars next to my resting place so that I could find them in the dark and preserve my night vision. I put on my shoes, coat and hat and headed downstairs and out my basement door. It worked. I was able to locate the comet immediately. The sky was fairly dark for my suburban neighborhood. I compared to M31 and estimated it to be 1 to 1.5 mag fainted than M31, putting it at 4.5 to 5 mag. Probably closer to 4.5 mag. I observed two Geminids before I went in, but I didn't spend more than 5 minutes looking for them. It's raining tonight and it doesn't look good for the next few nights here. It's nice to observe a moderately bright comet, but it doesn't excite as much as Comet Holmes in 2007-8 and IRAS-Araki-Alcock in 1983. I'm still waiting for the next Comet West or Hale-Bopp.

You must be logged in to post a comment.

Image of Niall MacNeill

Niall MacNeill

December 15, 2018 at 7:47 am

Is the time-lapse running backwards? In the cases where I've imaged the comet it is moving towards the ion trail.

You must be logged in to post a comment.

Image of Bob King

Bob King

December 15, 2018 at 10:41 am

Hi Niall,

Very perceptive! You're absolutely right. It IS in reverse. I don't know why that's so, but another time lapse made by the same photographer on Dec. 8 shows it moving in the correct direction. See here: http://spaceweathergallery.com/indiv_upload.php?upload_id=149755

You must be logged in to post a comment.

Image of wallymountz

wallymountz

December 17, 2018 at 7:19 am

Thanks for the great article Niall. I am certainly not in the same class as your previous posters, but because of your excellent chart, I'd thought I give it a try. I use a Star Blast 6i. I was able to find it by using the greenish color but it certainly was not a good image. Like you said, I probably need an 8-inch scope. Nonetheless, I gave it a good try.

You must be logged in to post a comment.

Image of Rod

Rod

December 17, 2018 at 7:51 am

2300-2330 EST last night I was able to observe 46P/Wirtanen again. We had 3 inches of rain move through my area from Friday evening until early Sunday evening but skies are clearing now. I used 10x50 binoculars and located comet 46P/Wirtanen in Taurus near 10:00 position of the Pleiades (as I viewed looking up high). It was in the area of 36 Tauri star (37 Tauri star in the area too). The comet was an easy large fuzzy shape in binocular view. I could faintly see with unaided eye. 36 Tauri at 70 degrees altitude and 226 degrees azimuth for my location at 2330 EST. The Moon was just past First Quarter and 21 degrees altitude and 252 degrees azimuth for my location. Bob King's chart shows the comet on 23-Dec-18 near 2000 EST will be close to the star Capella. That could make for a very good view in the telescope.

You must be logged in to post a comment.

Image of Tom-Reiland

Tom-Reiland

December 18, 2018 at 9:49 pm

First clear night here in Western Penna since the 13th of Dec. I grabbed my 10 X 50 binoculars and ran outside to see if I could spot Wirtanen, with the Moon about 30 degrees West of it. I saw a glow around a 5.3 mag star in Perseus, SAO 57229 (HR 1390). It is the Comet almost dead center in front of the star. Hard to judge the magnitude and size because of the Moon. I guess about 4 to 4.5 mag and at least 30 minutes in size as viewed through my binocs. Transparency is very good to excellent, but the neighbors' lights and the Moon hinder my observation of the comet and estimates. It seems that we seldom have excellent conditions like tonight without the Moon interfering. At least it's clear for a change.

You must be logged in to post a comment.

Image of Rod

Rod

December 19, 2018 at 8:28 am

FYI. The waxing gibbous Moon last night in Maryland along the Patuxent river farms, waxed eloquently so I did not view the comet last night. However, 17-Dec-18 evening I did near 8:30 PM or 2030 EST. The Moon at 2030 EST altitude 55 degrees and 192 degrees azimuth in Pisces. The double star Phi Tauri (52 Tau) altitude 60 degrees and azimuth 103 degrees in Taurus 2030 EST at my location. "Good view of 46P/Wirtanen in 10x50 binoculars and 25x telescope view despite waxing gibbous Moon in Pisces. Double star 52 Tau or Phi Tauri (split as double) and comet, same field of view (FoV) at 25x, 1.8 degree true FoV. Fuzzy shape comet. It was a fun seeing the double star in 7:00 position of eyepiece view (mirror reverse image) and comet near 1:00 position with the double star (Phi Tauri or 52 Tau) split in the telescope view. 46P/Wirtanen in Taurus tonight was framed by 4 stars in 10x50 binocular view, Phi Tauri or 52 Tau, 44 Tau, 41 Tau, and 42 Tau. The Moon was about 382000 km distance while I viewed and the four stars ranged from 90 to 420 light-years away from Earth. The comet is more than 30x lunar distance from Earth heading towards Capella encounter in Auriga on 23-Dec-18. The four stars in Taurus framing the comet in binocular view are all near 5th magnitude or a bit fainter."

You must be logged in to post a comment.

Image of Dave Mitsky

Dave Mitsky

December 19, 2018 at 7:36 pm

Due to a commitment, I was unable to observe until quite late last night. I stayed in the shadow of my neighbor's house to avoid direct moonlight and did runs with my 12x50 and 15x70 binoculars. The transparency was rather good and I was able to log Comet 46P/Wirtanen, Alcor and Mizar, Cr 65, Cr 69, Cr 70, Mel 20, Mel 25, M34, M35, M36, M37, M38, M41, M42, M44, M45, M47, M48, M67, and NGC 1981.

The comet was almost exactly at the position indicated at 12/19 7h on the finder chart posted at https://cometchasing.skyhound.com/comets/46P.pdf and was relatively easy to spot with the 15x70s, despite the bright moonlight and my red-zone skies.

I also viewed the star field that's discussed in the Binocular Highlight column on page 43 of the February issue of Sky & Telescope. It lies approximately five degrees north of Mel 25 (the Hyades) and includes Omega2 Tauri, 51 Tauri, 56 Tauri, Kappa1 Tauri, Kappa2 Tauri, Upsilon Tauri, and 72 Tauri.

Before going back inside, I spent a few minutes looking at the 11.8-day-old, 83.4%-illuminated waxing gibbous Moon.

You must be logged in to post a comment.

Image of Aqua4U

Aqua4U

December 25, 2018 at 6:36 pm

Bob.. always a pleasure reading your stuff! Thank you so much for being who you are and being there for us!

I saw Comet Wirtanen five nights in a row last week.. what a thrill! (The first night was the best - the rest thru too much haze and fog) This was my 56th visual comet observation and what what a 'doozy' it was! Now, it's Christmas Day and even though the comet has passed we have clear skies, I get another Christmas present! Am hoping to see this comet again tonight and that the tail(s) are more apparent..? It's all in the angle of the dangle!

Merry Christmas! Happy New Year.. and ROCK ON!

You must be logged in to post a comment.

You must be logged in to post a comment.