A Comet To Warm A Winter’s Night — How To See 46P/Wirtanen

This is Comet Wirtanen last night around 7:30 p.m. seen from just north of Duluth, Minn. An airplane blinked through the frame during the 1-minute, tracked time exposure with a 200mm lens. Through the binoculars, the comet looked like a diffuse glow with a brighter center. It was easy enough to see but overall vague and what most people would consider faint. Bob King

Some of us have been anticipating the close approach of comet 46P/Wirtanen for years. The time is nigh! Every 5.4 years, the comet drops into the inner solar system from out past Jupiter and occasionally passes near Earth at the same time it’s at perihelion or closest to the sun. This happy set of circumstances unfolds next month, when the comet reaches perihelion on Dec. 12 just four days before it zips closest to Earth.

Right now, 46P is slowly climbing northward through the stars of Cetus the Whale and visible from mid-northern latitudes starting about 7 p.m. till midnight. I found it in 10×50 and 8×40 binoculars last night both from a dark, rural sky and from my home closer to town. Although its magnitude or brightness stands right at the naked-eye limit of 6, the comet is a very diffuse glow in binoculars and generally still not visible without some kind of optical aid.

This beautiful image of Comet Wirtanen was taken on Nov. 28 and shows a big, fuzzy coma with a brighter center and a short, faint gas tail pointing northeast. Fluorescing carbon colors the coma green. Rolando Ligustri

But it’s expected to brighten three more magnitudes as it moves northward into into darker, more transparent skies. Throughout, Wirtanen will probably NOT show much of a tail, but it the head of the comet — called the coma — will become increasingly obvious in binoculars as we move into December. By that time, folks living in the country should have no problem just looking up to the left and below the Pleiades star cluster to see it with the naked eye  — 46P will look like a ghostly, glowing patch in the sky.

You can use this map to help you find 46P over the next few weeks. I set it for around 9 p.m., but the comet will still be very close to the marked positions earlier in the evening and later at night. Key bright stars are circled. I’ve also added a couple hints like lining up stars or following an arc of stars to help point you to the comet. Click the map, then right-click to save and print out for use outside. Stellarium with additions by the author

Right now, it’s very difficult to spot from light-polluted locations in binoculars, but if you live in the outer suburbs or have access to a rural sky, it’s relatively easy if you know just where to look. That’s why I’ve included a map that includes with easy, bright stuff like Aldebaran, Orion and the Pleiades to help you get oriented.

If you’re not a fan of black stars on a white sky, this chart’s for you! Share these maps to help others see the comet.  Stellarium with additions by the author

For the next week or so, the comet will be moving across Cetus and Eridanus, big, gangly constellations with few bright stars, so it will take just a bit more effort to find. Your key stars / references are the Pleiades, Aldebaran (Taurus’ brightest star) and Menkar, the second brightest star in Cetus and equal in brightness to several of the stars in the Big Dipper. Use them and the other labeled stars to shoot a line to the comet or include the comet as an apex in a triangle. I always find that if make my target part of a simple pattern — line, triangle, square — involving easy-to-see stars, I have a much better chance of spotting it.

Comet Wirtanen brushes closest to Earth on Saturday, Dec. 16 when it will pair up with the Pleiades. We have until about Dec. 13 with little to no interference from a bright moon. After that, the moon gets brighter and higher, diminishing the comet’s brightness and its contrast with the sky. You can also elect to stay up late AFTER moonset, in which case you’ll have through Dec. 19 to see 46P in a dark sky. Starting on the 20th, the moon will be inescapable. To plan your observing nights, check your local time of moonset and moonrise here.

Stop back here for updates on the comet in case it does crazy stuff like go into outburst. Yes, comets have “fits” when they suddenly brighten as fresh ice gets exposed due to solar heating. That ice vaporizes in a quick, carrying off loads of fresh dust that shines brightly in sunlight.

While 46P is no Hale-Bopp, I want you to be excited about seeing the comet and wish you clear skies for a good look. Onward!

5 Responses

  1. Edward M. Boll

    Should be a good comet to see with the Gemini’s. I have yet to look for it. It is still quite low and the last 5 observations into COBS only averaged a magnitude of 6.3. Right now I am excited about comets 64 and 38. But after Dec.1, I will start attending to 46. Comet 38 and V1 should both be at their brightest on Nov. 30, even though V1 is hidden by the Sun.

  2. Edward M. Boll

    Pardon my ignorance. I understand a lot of terminology for comets, but I am not quite sure what APP T stands for. Often it is accompanied by a number and letter. I have noted that for naked eye it is 0.0. By the way Wirtanen reports are now averaging 5.6, and the last report on COBS put comet 64 at magnitude 8.2, about 2 magnitudes above last months predictions.

    1. astrobob

      Hi Edward,
      No problem. APP means aperture of the instrument in cm and T stands for “type” as in “B” for binoculars, “L” for reflecting telescope and so on.

  3. Richard K. Mitchell

    I have been observing comet 46P over the last few nights and I can see it with 10×50 binoculars with only a little difficulty, but the skies are too bright to see it with the naked eye. In binoculars it reminds me of the M33 Galaxy, maybe a bit brighter.

    1. astrobob

      Hi Richard,

      Good description — thanks for writing. I finally got a good view from a dark sky last night just north of Duluth, Minn., and the comet was visible without too much difficulty with the naked eye. Mag. 5.5. It’s’ coming along nicely.

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