How To Sidestep The Moon And Stay On 46P/Wirtanen’s Tail

This map tracks the comet through Dec. 25. I chose to show its position at 8 o’clock Central Time but it will be close to that location even if you observe it earlier or later that night. By good fortune, the comet is brightest when located near the familiar Pleiades and Hyades. On the 22nd and 23rd it passes very close to the bright star Capella in the constellation Auriga. Although the moon will be full then, you should still be able to see in binoculars. Chris Marriott’s SkyMap with additions by the author

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, but 46P is large and diffuse and best seen in a moonless sky. Almost everything other than the moon and planets is best seen in a moonless sky!

Here’s the comet on Dec. 10 from near my home taken on a tracking mount with a 200mm telephoto lens. It’s currently about magnitude 4.5. Skywatchers in large cities are having a difficult time seeing it, but from suburban areas it’s visible in binoculars and easy to see with the naked eye in the country. Look for a blob with a brighter center.  Bob King

I’ve prepared a fresh map to help you follow our fuzzy friend through Christmas and a table of sorts 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 then check the moonrise and moonset calculator to find exactly when the moon sets where you live. Because the moon has been gaining on the comet (as it moves east in its orbit), you’re going to have to stay up later and later for moonset.

Here’s the same view as above but with a 35mm lens, wide enough to include the comet, Seven Sisters cluster (top, left) and the Hyades (left, center) in the same view. Bob King

Best comet viewing times. If you go out after the moonset times, the sky will still be dark and ideal:

  • Tonight (Dec. 12) — Anytime. Moon’s not a problem.
  • Thurs., Dec. 13 — Moon starting to brighten the sky. Sets 10:30 – 11 p.m. local time.
  • Fri., Dec. 14 — Moon at first quarter phase (half-lit). Sets 11:30 to midnight. Some light but still not a comet-quencher.
  • Sat., Dec. 15 — Moon sets 12:30 – 1 a.m. Sunday morning.
  • Sun., Dec. 16 — Moon sets 1:30-2 a.m. Monday morning. Getting bright now.
  • Mon., Dec. 17 — Moon sets 2:30-3 a.m Tues. morning.
  • Tues., Dec. 18 — Moon sets 4 a.m. Weds. morning.
  • Weds., Dec. 19 — Probably the final moonless night for diehard observers. Moon sets around 5 a.m., and the comet is low in the northwestern sky.

Dark skies return during early evening hours starting Dec. 24. While it’s always exciting for long-time comet observers to see one with the naked eye, the average person won’t be visually impressed by this fuzzball. It doesn’t show a tail (except a short stub in a telescope) and it’s basically little more than soft, diffuse glow. You could compare it to a painting done in minimalist style vs. a Van Gogh. As so often happens in astronomy, it’s what you bring to the object that helps you to appreciate it. Knowing you’re looking at a kilometer-wide spinning ball of dusty ice as ancient as anything in the solar system is just cool. And it will soon be less than 30 times the moon’s distance as it swoops by Earth.

15 Responses

  1. Edward M. Boll

    I am not a late night observer most nights and I know I am in for a challenge but to me it will be a form of victory, if I can spot the comet even when the Moon is full. Of course I am looking forward to after Christmas when the comet will be fainter but then up high in a moonless sky.

  2. kevan hubbard

    I’ve aspied the comet twice now.first time from a pretty dark area and I am certain that in such areas you can see it naked eye.tonight I saw it through my 8×25 monocular from a very light polluted village,a light polluted village I hear you say well the light mainly is not from the village itself but from petrochemical works to the south,and a rather poorer view.although tonight I didn’t have a star map with me and found it from memory of my last sighting,basi basically checking in a line up to m45.

  3. Edward M. Boll

    I averaged the last 6 cons sightings and they averaged a magnitude of 4.2, so most likely it will just become a 4th magnitude comet at best. I am typing this at the minute of perihelion.

    1. kevan hubbard

      I think that this is the brightest comet I’ve seen since the Holmes comet. I saw another,cant remember it’s name about 5 years back,but it was dimmer.

      1. Edward M. Boll

        May I suggest the dimmer comet 5 years ago may have been 2011 L4 Panstaars. I just rechecked those coordinates, and it was about magnitude 1-2 in early 2013, but we could not see it easily until it was 20 degrees over the horizon and by then it had faded to magnitude 5 or 6.

        1. astrobob


          I remember that one. Nice little tail and easily visible naked eye at dusk. Great in a small scope with a bright, pale yellow nucleus.

        2. kevan hubbard

          I think you are right about panstars infact I recall two comets at a similar time.the Holmes was the last bright one and took everyone by surprise as it was expected to be dim but got to 3rd magnitude.

  4. Blake

    Cool site, just found it (and bookmarked), I’m heading outside in about 30 minutes (where it’s currently 1 degree) and this should be very helpful in finding 46P/Wirtanen! I’ve learned in Vermont, you better go outside if it’s clear, because that’s a rare thing. Tomorrow much warmer, hopefully the clouds stay away.

  5. Edward M. Boll

    Bob, you have a good memory to remember that one concerning all of the comets that you have seen. One who wrote mentioned a comet in 2007 about the same times as Holmes. Seems like I vaguely remember one. When I checked the records there was one Loneos but it apparently faded fast already magnitude 8 when it got about 15 degrees high. Maybe I was thinking of the other bright 2007 comet McNaught. Because of an extremely south declination I only saw it 3 evenings in January. But it was so bright you could use that comet as a guide to finding Venus!

    1. astrobob

      Hi Edward,
      McNaught was amazing. I remember seeing it shortly after sunset in late-Dec. or early Jan. with a bright, easy-to-see tail. I got a few nice images of it with a long lens at the time.

    2. kevan hubbard

      That one was very far south as I remember reports from new Zealand about the time it reached our northern skies it had faded.the Holmes was on the other hand was high up almost on the canopy and brighter than I thought,2.8 magnitude. I think after the hale bopp the Holmes would be the brightest at least in the northern skies.

  6. Richard K. Mitchell

    I observed comet 46P in 10×50 binoculars at about 4th magnitude last night and after my eyes dark adapted for about 20 minutes I could see it (barely) with the naked eye. I live in Albuquerque NM so the skies are only moderately dark. Oh,by the way I even saw a few Geminids!

  7. Edward M. Boll

    Well, I am at 44 degrees north latitude and I remember seeing McNaight with nothing but my own eyes easily half hour after sunset, not quite a daylight comet this far north but close.

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