Sayonara, Comet Wirtanen! / Stars, Planets, Moon Parade At Dawn

Comet 46P/Wirtanen slows down and fades as it travels from Lynx to the Big Dipper in the next couple weeks. I’ve marked the comet’s position at 5-day intervals. You can interpolate between the marks for other days. Stars are shown to magnitude 6. Start at Capella and use it and other nearby stars like Delta Aurigae, 2 Lyncis and 15 Lyncis to help you point your binoculars toward the comet. Stellarium with additions by the author

As we come to the end of December, comet 46P/Wirtanen is fading. Comets can be unpredictable , but this one came pretty close to expectations, missing its brightness prediction by just one magnitude. Instead of an easy magnitude 3 (one level below the Big Dipper stars), it reached a dimmer magnitude 4. If you lived in or near a large city, 46P proved challenging. But from outer suburbs, it was visible in binoculars and from dark skies, you could easily spot it with the naked eye. I saw it routinely many nights because — incredibly — we had a week of clear weather when the comet was at its best at mid-month.

A recent photo of the comet from Dec. 26 — still a big, fuzzy ball with a brighter center or nuclear region. The stars are trailed because the photographer tracked on the comet during the time exposure. Gianluca Masi

If I could have wished for one thing it would have been a brighter, more obvious tail. That’s where much of a comet’s beauty lies. Wirtanen managed only a short, faint stub that required a good-sized telescope to see. Had we been able to view the comet from the side, the tail would have been more obvious, but as it was, 46P was best and brightest when it was at opposition to the sun with its tail pointing away from us and mostly hidden behind the fuzzy coma.

Nature is what it is. Certainly, the comet had its own sort of ghostly charm. And still does. You can still see it in binoculars as it crawls across the long, skinny constellation of the Lynx and from there into Ursa Major the Great Bear. The bright, twinkly star Capella, halfway up in the northeastern sky at nightfall, will help point the way. 46P lies about two fists to its lower left. Use the map provided, start at Capella and star-hop to the northeast until you land on a fuzzy patch.

Two nights ago (Dec. 28), I easily spotted 46P in a dark sky but noticed that it had faded to about magnitude 5. Although difficult to see with the naked eye, I saw it easily in binoculars as a soft, glowing patch of light. For the next 10 nights or so, without a moon to muss the view, the comet should remain visible in 40-50mm binoculars from reasonably dark skies. Once the moon returns, most casual observers will let go of Wirtanen and move onto other things. Even as you do, know that 46P/Wirtanen will hang out in the Great Bear all the way through early March, fading all the while.

Look for a prett lineup of planets, stars and the moon at year’s end and for the next few mornings. On Jan. 1, a thinner crescent will pass just a few degrees from Venus, a delightful sight. Click the image to find your sunrise time, so you can plan your morning outing. Stellarium

Winter’s a wonderful season for early morning skywatching because of the late hour of sunrise. I can get up a little before 7 and still see the brighter stars and of course the planets, Venus in particular. Tomorrow morning, the last day of the 2018, we have a great lineup at dawn that includes two stars, three planets and the waning crescent moon. Let’s go down the line from highest to lower: Spica, Virgo’s brightest star, followed by the moon, Venus, Jupiter and Mercury. We’ll throw in Antares (Scorpius’ brightest star) even if it’s out of line just because we’re feeling magnanimous at year’s end.

The map depicts the sky about an hour before sunrise. For the best view find a location with an open view to the east-southeast. Mercury will be quite low at map time, so you may want to wait a bit till it rises higher, about 15-20 minutes later. All the others should be easy to see.

12 Responses

  1. Dale Jacobs

    Thanks for the continued coverage of this comet Bob. What a great Christmas present it was and is! I’ve seen it on 7 nights so far through my 70mm binoculars. The binos performed much better than my telescope, a 12 1/2″ f3.6 Newtonian.This was due in no small part to the comet being so big and diffuse. Did anyone else notice this effect?

    1. astrobob

      You’re welcome, Dale. Except for detailed looks at the nuclear region, I enjoyed the overall appearance of the comet in binoculars more than in a telescope. It was too big in the scope — filled the field.

  2. Edward M. Boll

    I have devised my own formula, now exactly scientific. I divide magnitude into degrees high and then multiply degreesvtraveled in a week since most travel farther when near the Earth. With that Wirtanen has faded from a high December 21 from about 5700 to 3350. That lower number is at least 9 times that of the second brightest, Swift Gehrels.

  3. Witranens tail was invisible *because* it was so bright and large. This comet had the perigäum and the perihel at nearly the same time. That means that it was in opposition to the sun in December. The tail is directed away from us. Perhaps we see more of it in the following weeks.

    1. astrobob

      Hi Uwe,
      Yes, that would have been good to include to explain why it appeared so short — thank you for pointing that out! I will add it now.

  4. Dale wrote
    > The binos performed much better than my telescope, a 12 1/2″ f3.6 Newtonian.

    Pale, diffuse objects can be seen best if they have a angular diameter between 0.1 and 1 degree. Even in binoculars it was larger, the easy detectable part was the inner one. With a Newtonian, you minimal magnification is simply too large.

  5. Hi Bob! Another rare beauty! 🙂 I’ve been following you since I lived in Duluth and have happily continued after we moved in 2012. Thank you for sharing your beautiful photography and commentary! Wishing you a very joyous New Year and looking forward to seeing many more in 2019! Kind Regards, Sandra Bacigalupo

    1. astrobob

      Thanks for your kind words, Sandra. And the wishes, too. I send them back to your way and wish you clear nights ahead, especially for the Jan. 20 total lunar eclipse visible from Duluth. More details on that later 🙂

  6. Mike McCabe

    Really enjoyed this comet, Bob. I’ve used your map to follow it from Cetus through Eridanus, back to Cetus and all the way across to Lynx. I’ve also seen it in scopes ranging from 80mm to 12″, but by far the best view was through my mounted 20×80 binos. It’s been visible in 10×50’s every clear night except the 22nd (full moon) from my Bortle 6/7 skies, without fail. Tail or no tail, this has been our best comet in quite some time.


    1. astrobob

      Hi Mike,
      It’s sure been fun, hasn’t it? Plus there were some great photo opportunities when it was near the Pleiades. Great way to wind up the year, I’d say. Happy New Year to you, Mike as we look forward to the upcoming total lunar eclipse.

    1. astrobob

      Hi Edward,
      I wondered about that. Thanks for getting back on it. Happy New Year and let’s hope for a bright, new discovery in 2019!

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