What’s Going On With Comet SWAN?

Comet SWAN glows glows green-blue in morning twilight on May 13 from central Arizona. Chris Schur

Like many of you I’m hoping to see Comet SWAN for the first time at the end of this week or early next. For the northern U.S. the comet is still very low in the morning sky in twilight, but it climbs to around 5° by Monday, May 18, high enough to attempt in binoculars. Use the maps I posted earlier and start looking for it about 2 hours before sunrise around the start of dawn. If you live in the southern U.S. the comet’s not quite as low, so go for it now.

I have some disappointing news. Instead of brightening over the past week and a half as expected, SWAN has faded. For instance, it should be around magnitude 3.5 right now but it’s 5.5 or two magnitudes fainter (about 6 times dimmer than expected). Comets are dodgy like that. Prone to busting expectations. Things could easily go the other way, too with SWAN suddenly flaring when we least expect. My hunch is that it will likely get brighter because the comet is still two weeks from its closest approach to the sun on May 27.

The Oort Cloud, located far from the cozy realm of the planets, is home to billions of comets that periodically drop into the inner solar system. Its distance is given in A.U.s One A.U. or astronomical unit is equal to 93 million miles (150 million km) or the distance of the Earth from the sun. Wikimedia Commons

Comets that hail from the distant Oort Cloud and take thousands of years to orbit the sun often brighten up fast and soon. For many it’s the first time they’ve entered the inner solar system and truly “felt” the heat of the sun. The warming rays rapidly vaporize the comet’s ice which in turn releases the dust and gas that glow brightly in the sunlight. Sometimes, after that initial outburst, a comet stalls or even fades, having used up all of its easily vaporized ice. That’s what appears to be happening with SWAN right now.

This sketch I made of Comet ATLAS (C/2019 Y4) reveals a beautiful, faint tail streaming away from the coma or head on May 11. A small, separate “puff” from fragments ahead of the coma create a second smaller, fainter coma. Bob King

But it’s the comet’s very unpredictability that makes me hold out hope for a good show. That’s also one of the reasons I like comets so much aside from their beauty. Unlike many objects in the sky they change on a relatable time scale of days and weeks instead of centuries and millennia.

Take a look! A fragment within Comet ATLAS Y4’s tail appears to be growing a tail of its own. Photo taken on May 13. Nick James

Another great example of cometary whimsy is the recent breakup of the naked-eye comet that wasn’t — ATLAS Y4. Its core fragmented into many pieces in April, and the comet faded. But the dust released when those fragments vaporized helped ATLAS grow a beautiful if faint tail. Recently one or more of the pieces has gone on to become a comet-within-a-comet. My drawing shows a second object but the photo taken by Nick James, director of the British Astronomical Association’s Comet Section at the photo Nick James revealing a full-fledged comet growing inside the original.

From left: Mars, Saturn and Jupiter gather on April 30 at dawn. Bob King

Comets stoke our sense of wonder as do many other sky sights including the much-easier-to-find planets. When you’re out looking for the comet take in the sweep of the three morning planets: Mars, Saturn and Jupiter. The latter two are paired up 4.5° degrees apart low in the southern sky at dawn with Mars three horizontal fists off to the left (east). The thick crescent moon hangs a few degrees below Mars tomorrow morning (May 15).

Hang with the sky and you’ll have a happy life. A good friend who saw Nick’s photo today told me that even fragmented (like the comet) you can continue living and sharing beauty. Since we’re all a little fragmented I couldn’t agree more.

Special note: I had a very enjoyable interview with John Michael Godier, creator and host of Event Horizon, about my recent book Urban Legends from Space earlier this month. The episode is titled Jupiter a Failed Star? Nemesis?  You can listen to it here. Let me know what you think. We touched on many topics but always returned to the importance of science and the scientific method to get us through dark times. Urban Legends and my other books are available on Amazon.com, Barnes and Noble and Indiebound.

11 Responses

  1. Nathan

    I’m coming your way from John Michael Godier’s YouTube channel. I loved your interview and plan on following your blog and such. Keep up the great work! You’ve got a new fan in Wisconsin!

    1. astrobob

      Hi Nathan,
      I’m so glad you enjoyed it. Thank you very much for saying so. Glad to have you on board. Never hesitate to ask a question.

  2. Edward M Boll

    What would be easier to see? Swan now possibly magnitude 8, 3 degrees high, or Atlas at magnitude 9, 8 degrees high.

    1. astrobob

      Edward,
      That 8.0 observation is a CCD camera magnitude not visual. I saw ATLAS last night and it was a beautiful if faint sight. It’s about 9 with a small, 2-minute coma and very diffuse in my 15-inch. But what a beautiful tail! SWAN would look little brighter at 3° altitude but will very soon reach 5° and should be visible in binoculars. I’ll be out Monday for a look.

  3. Edward M Boll

    That is good to hear. That is all I had to go for on Swan. There was only one observation of it out of 20. It looks like Lemmon at 8, and Neowise at 9 are doing as well as can be expected. I think probably the easiest to see is T2 at 9, very well placed.

  4. Edward M Boll

    One observation came in with Swan in 25 magnification. Cloudy here. I may try with 20 tomorrow. Apparently Atlas is now 10.

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