Will Comet L4 PANSTARRS Live Up To Expectations? A Reality Check

Comet C/2011 L4 PANSTARRS passes near the globular cluster NGC 6541 on the morning of Jan. 16, 2013 as photographed from Castlemaine, Victoria, Australia. The comet measures about 2 arc minutes in diameter with a 7-minute long tail. Click to see more southern comets. Credit: Michael Mattiazzo

Sometimes that shiny new phone or car doesn’t quite live up to expectations, but we often  overlook their deficiencies and make our peace. We may have to do the same with Comet L4 PANSTARRS.

Observers in the southern hemisphere have watched the comet closely since it emerged from the solar glare last month. It’s presently loping along through Corona Australis the Southern Crown and visible shortly before dawn for those living down under. Not too many months ago, PANSTARRS was forecast to reach a brilliant magnitude 0 (equal to the star Vega) come early March this year. In recent weeks however, the comet has been lagging.

Amateur astronomers have noticed that its rise in brightness has been slowing down or plateauing of late. As of Jan. 19, 2013 the comet is a small, dense fuzzball of about magnitude 8 with a short tail pointing west. Binoculars show it as a dim glow.

With less than two months to go before the “big show”, this lag has made some ardent comet watchers revise their expectations of just how bright PANSTARRS will become.

Lightcurve of Comet C/2011 L4 PANSTARRS. Each black dot represents an observation of the comet. The bottom line (axis) shows time, the vertical axis, brightness. PANSTARRS is clearly getting brighter over time but not as fast as expected. Credit: Seiichi Yoshida

Seiichi Yoshida, a Japanese amateur astronomer who maintains the excellent and most useful Weekly Information about Bright Comets site, originally pegged the comet at magnitude 0 in March but has now revised his lightcurve (graphical representation of a comet’s rise and fall in brightness) to show PANSTARRS topping out closer to magnitude 3 at best. His estimate is based upon past as well as the most recent observations.

Comet L4 PANSTARRS photographed on Jan. 19, 2013 with a 200mm lens and time exposure. Credit: Rob Kaufman

If this holds true, what does it mean for comet watchers? A magnitude 3 comet is 15 times fainter than one shining at mag. 0. While still visible with the naked eye, such a comet would not be a visual spectacle. Given that PANSTARRS will be brightest when relatively near the sun in evening twilight, it would appear faint without optical aid, but still be a stirking sight in binoculars and telescopes.

Of course this could change again, so I wouldn’t get too worried yet. Comets are wonderful to follow in part because of their unpredictability. L4 PANSTARRS may yet have a few tricks up its sleeve. Stay tuned for more updates in the coming weeks.

15 Responses

  1. H.Bob

    When will the next highly visible comet appear in the northern hemisphere. Do you recall how bright Hale-Bopp was in 1997? Any AstroBob photos of that one?

    1. astrobob

      H. Bob,
      L4 PANSTARRS may still turn out well, but I’ll put my money on Comet C/2012 S1 ISON. That one may rival Hale-Bopp come December this year. Hale-Bopp was around zero to -1 magnitude at best. Yes indeed I took many photos of it back in the days of film.

      1. Mark

        I’m always surprised by comparisons to Hale-Bopp as though it were a Great Comet. Sure, it was nice, but not terribly impressive, especially when compared with Comet Hyakutake just one year earlier. I think anyone who saw both would rate the visual impact of Hyakutake far higher. Of course, we take what we can get!

        1. astrobob

          A lot of people were more impressed with Hyakutake. Even though it had one heck of a tail, I was more taken with Hale-Bopp. It was brighter and lingered around a long time in the naked eye range.

    1. astrobob

      That MIGHT happen with PANSTARRS, but more and more it’s looking fainter. The most optimistic forecast is mag. 2 or as faint as 3.

  2. Edward M. BOll

    I am not making any predictions on ISON yet, but the most optimistic puts it at -21 magnitude. Even if it got that bright, it would not be brighter than Venus for more than 5 days.

    1. H.Bob

      -21 ?? Is that the brightness from Earth? I thought Venus was around -4 from what I have been reading here. A bit confused.

      1. astrobob

        H. Bob,
        That estimate is way, way over the top! I’ve heard estimates of -13 (which also seems a bit much). If that happens, it would only be around the time of perihelion when the comet is very close to the sun and only visible in the daytime sky. Of course I hope it does! With proper precautions, ISON might be visible to the naked eye despite the solar glare as a bright, small star-like point near the sun. Venus is around -4 magnitude and very bright when far from the sun in a dark sky. Close to the sun, it’s too faint to see with the naked eye.

        1. H.Bob

          Thanks AstroBob. I’m trying to get a feel for the magnitude scale so just wanted to double-check my understanding.

  3. Lukas

    Starry Night programs show the tail of ISON being visable all night in Yellowknife Canada… lets all hope! Panstarrs might be a bust!!! But you never know… we will see after perehelion..

  4. mike

    It was a bust last night, barely visible in Oklahoma even with strong binoculars. Not visible with the naked eye. Only found since it was next to the crescent moon, unable to find it the night before. sigh

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