Updates on Comet PanSTARRS
Comet PanSTARRS (C/2011 L4) peaked out at roughly magnitude +1 and is now fading with a very wide tail. We covered the comet in the February and March 2013 issues of Sky & Telescope. Here's the latest:
April 23: Crossing Cassiopeia. The comet is heading north, in Cassiopeia through the end of April. It's much better seen (from north temperate latitudes) before dawn now than after dusk. The comet has faded to about 6th magnitude, detectable in binoculars and very respectable in a telescope. Use the finder chart in the March Sky & Telescope, page 51.
Its tail has grown hugely wide! It's a fan spanning 160° in this photo of the comet passing the irregular galaxy IC 10, taken remotely by Rolando Ligustri on April 22nd.
April 10. It's moving farther north and fading on schedule, now 4th or 5th magnitude. Here are images from April 1 to 10 taken from the Orkney Islands, Scotland, by John C. Vetterlein of the Auroral & Magnetic Observatory in Rousay, latitude 59° north, where the comet is nicely circumpolar.
April 2. The comet passes the Andromeda Galaxy in the first week of April. They're closest (2° apart) on the evening of the 3rd and morning of the 4th. See article, Comet PanSTARRS Offers M31 Photo Op.
March 29. From Norway comes the gorgeous picture below, as PanSTARRS approaches the Andromeda Galaxy.
March 21. Last night Sean Walker, Sky & Telescope's imaging editor, took the shot below:
Walker writes, "Tried some wide-field shots tonight. Should have brought a slightly longer lens! 18-55mm zoom lens at 55mm, ISO 800; 60-second exposure with 0.5x tracking."
March 20: Broadening tail. The farther north you are now, the higher the fading comet appears in twilight and the darker the sky you can see it in. As predicted, this means that imagers are becoming able to capture more of the comet's big, wide, detail-filled tail — though its surface brightness is mostly too low to be seen visually.
For instance, last night Michael Jaeger in Austria (latitude 48° north) took the dramatic image below with the sky background suppressed and contrast enhanced.
March 18: Fading but higher. John Bortle writes, "I've been troubled for days regarding the broad range in reported magnitudes for this comet in recent days. Some ranked it near zero magnitude, while so many were indicating the comet was difficult or impossible to detect with the unaided eye.
Well, last evening [March 17th] I settled the matter as far as I am concerned. From careful observation I determined a total magnitude for the comet's head of only +2.6 , noting that even in a very clear sky the comet was only glimpsed with the unaided eye as twilight deepened. In my opinion the general lack of good comparison stars nearby has led to observers going far afield to stars much higher up for comparison, and then applying excessive atmospheric-extinction corrections to their estimates."
Many others disagree. Alan Whitman writes: "In my Canon 10x30 IS binoculars in excellent transparency, the nucleus was FAR brighter than adjacent magnitude 2.8 Gamma Pegasi. Magnitude 1 is a lot closer to its current magnitude, in my opinion."
Impressive time-lapse movie of PanSTARRS from the STEREO-B Sun-observing spacecraft, with coronal mass ejections passing by.
March 14: A little star with a dim tail. Many, many people saw it last evening, aided by the crescent Moon, but many others failed. S&T's Tony Flanders writes: "I caught it from the balcony of my mother's apartment at 7:55, 54 minutes after sunset [at latitude 41° N]. I'm sure I would have spotted it much, much earlier except that I had been looking too high, too far left, and for a very different kind of object.
"I'm sure this comet will never be obvious to the unaided eye from our latitude, much less spectacular. But it sure is a beauty through my 10x30 image-stabilized binoculars. I was looking for something larger and more diffuse; in fact, it's tiny and intensely bright, with a nearly stellar head (at 10x) and a short, very bright tail."
From S&T's Sean Walker at 43° N: "I was able to observe the comet with 70mm spotting scope and shared some great views with about 30 people. The comet was naked-eye visible, though barely, from about [50 minutes after sunset] until it was in the trees 15 minutes later.
"Not much of a tail, perhaps 1° with averted vision naked-eye. Never obvious; it was very reminiscent of the views we had in 2007 of Comet McNaught, though fainter. Still very orange due to low altitude. "This photo by UK amateur Jamie Cooper approximates the view through a small telescope perfectly. It looked exactly like this in my 70mm f/5 spotting scope:"
"But I agree with Tony that this will never be a showstopper. Edwin, Imelda, and I pointed out the comet to several passersby, and they had a very, very difficult time seeing it naked-eye, and also had difficulty finding it through binocs. And yet they had the three of us standing right next to them explaining in detail where to look. We also had airplanes in the sky right near the comet, and we used the positions of those planes to help these passersby find the comet."
Tonight, March 14th, look about two fist-widths at arm's length below the crescent Moon and perhaps a bit right.
March 13: To the Moon! It's getting easier now; each evening the comet is a little less low in the twilight. Last night lots of photographers shot the little "smudge of light" with the thin crescent Moon:
In tonight's twilight, look for the comet a fist-width at arm's length below the thicker Moon. Best view is roughly 40 minutes after sunset. You'll need an open view low due west.
Another nice Moon-and-comet pic from Fred Espenak, plus a movie of the two setting.
March 11: Speck, not spectacle. Last night lots of people in the north temperate latitudes finally began picking up the comet for the first time, but usually with binoculars, and only if they knew just where to look. Keep trying. It's moving a little higher out of the bright depths of twilight every day now.
This image matches a lot of people's visual impressions:
March 8: North to Florida. Longtime amateur astronomer Jim Brant writes from Homestead, Florida, latitude 25° N:
"I spotted the comet naked eye at 7 p.m. tonight (March 7th). It is much fainter than recent photos from the Southern Hemisphere, which is expected as they are time exposures. It looks like a faint straight jet contrail, about a degree long and fainter than I expected. It's a pretty sight in my f/6.25 80mm refractor at 11x."
Meanwhile, longtime Sky & Telescope comet analyst John Bortle writes,
"In spite of claims in recent weeks that the comet had suddenly begun to brighten rapidly, such was never the case. PanSTARRS' behavior has been very normal and uneventful since the beginning of the year.
"Now at its peak brightness, between +1.5 and +2.0 and passing its closest to both Sun and Earth, the comet will shortly begin a long, slow episode of fading as it retreats from the inner solar system. The comet's dust tail, seen so far only as a stubby appendage, should begin to apparently lengthen as the comet moves away from the brightest region of twilight.
"However, the tail is unlikely to attain spectacular proportions because of its almost perfectly side-on presentation to us, resulting in a low surface brightness. While comet dust tails can often be very broad, they are thin in cross section, making the density of PanSTARRS' tail very low from our current perspective. Long-exposure images of the comet in about 2-3 week will reveal far greater tail lengths than anyone will be able to detect visually."
March 7: Terry Lovejoy in Australia estimates the comet at about magnitude 1.5 as of March 6.38, after correcting for low-altitude atmospheric extinction that made it look like about magnitude 3.0.
March 6: Moving north! The latitudes where Comet PanSTARRS can be seen low after sunset are moving north day by day. The Southern Hemisphere has had a good look, as the reports and pictures of the last few weeks testify, and it's still in view there; here's a March 4th pic from Trevor Sellman in Australia.
But the zone of good visibility is heading north now through the tropics. For instance, last night (March 5th) came this report from "Preston in San Miguel de Allende" in central Mexico, latitude 21° N. He was at an elevation of 6,000 feet, certainly a big advantage. "I observed PanSTARRS last night at about 6:50 p.m. for 10 minutes before it descended into the smoke/haze. It was easily naked-eye visible, and the tail could be made out without binoculars."
How soon will you pick it up? Bring those binoculars.
And here in Sky & Telescope land, we're about to get a two-day snowstorm....
March 2: Still brightening.... Mariano Ribas writes from Buenos Aires: "Today (March 2nd) I could again see comet PanSTARRS in the twilight with my unaided eyes, but much easier than only two days ago. I estimated it a visual magnitude of 2.3, a half magnitude brighter than on Feb. 28th. With the help of my 10x50 binoculars, the comet looked very bright, with a coma very concentrated again, very stellar in appearance, and a tail at least 1° long. Each day the comet gets better and better!"
March 1: Yep, naked eye! From Buenos Aires, veteran comet observer and science journalist Mariano Ribas writes,
"Since last night (Feb. 28th) comet PanSTARRS is a naked-eye object in the Buenos Aires sky, despite its low altitude (a few degrees over the SW horizon at evening twilight) and the strong urban light pollution. I estimated it a magnitude around 2.8. Almost a full magnitude brighter than just 3 days ago!
"With 10x50 binoculars, the comet looks yellowish, and the center of its coma looks not only brighter now, but also shows a very high degree of concentration. Also, I could easily see a 1º tail against the light blue sky of twilight.
Feb. 28: "Magnitude 2.6." From southern Australia Michael Mattiazzo posts, "End of nautical twilight. At 6° altitude the comet and small portion of tail clearly visible with the unaided eye, appearing marginally fainter than comparison stars Alpha Gruis (mag. 1.8) and Alpha Pavonis (1.9). In 25x100mm binoculars, the dust tail measured 1.5°.... The ion tail was not visible visually but is at least 2° long in PA155° on a 3-minute exposure using a Canon 60Da camera and 300mm lens."
His picture, much cropped in, is at right. Here's a wider pic he took on February 23rd.
Feb. 25: Waiting time. As of February 20th PanSTARRS was reported at 4th magnitude with a 1° tail. Approaching the Sun from the south, it's now becoming lower as seen from the Southern Hemisphere.
Our longtime comet columnist John Bortle writes that its consistent behavior in the last six weeks suggests "a peak brightness of about +2.2 on or about March 10th, with a slow fading thereafter taking the comet to about magnitude +5.0 by month's end.
These parameters also imply a resemblance to Comet Mrkos, 1957 P1, both in regard to observational geometry and brightness. If this is true, PanSTARRS could put on a fairly respectable showing during late March and early April although heavily impacted by the inconvenient timing of the full Moon.
"If PanSTARRS attains 2nd magnitude it should exhibit a fairly broad, strongly curving dust tail between 5 and 15 degrees in extent. How much of this will be suppressed by the bright twilight in mid- to late March is, of course, open to question. Those with the lowest western horizons and clearest, darkest, skies are likely to be favored, since this will allow following the comet as late as possible in the dying twilight glow."
Feb. 17: The comet is still a Southern Hemisphere object, and observers there who are using optical aid are pretty happy with it. Michael Mattiazzo posts, "I imaged C/2011 L4 on Feb 15.75UT. It is looking quite impressive through 25x100mm binoculars; a 'great binocular' comet. The ion tail appears 2° long, and the much more visible dust fan is 50′ long, spanning an arc of 45°. Visual estimate was affected by light pollution, low altitude and twilight, but it is not fainter than magnitude 5.0."
Feb. 12: Gas tail appears; comet still on track for 3rd-magnitude peak. So far Comet PanSTARRS has shown an unusually large dust-to-gas ratio, but the thin, straight gas tail (pointing directly away from the Sun) has appeared and grown as the comet nears the Sun.
Meanwhile, the comet overall has been brightening smoothly along its new predicted light curve that peaks at about magnitude 3 on the March 10th perihelion date. See light curve (scroll to bottom), with observations (black dots) overlaid on the original and new predictions (gray and red lines).
Jan. 31: Dust-tail simulations. Uwe Pilz in Germany has created computer simulations of PanSTARRS' predicted dust tail. It curves away to the left of the straight gas tail symbolized on our charts above and below. On Pilz's graphs, the blue line is the direction away from the Sun; align this with the tail symbols on our charts. The black "1.0 grad" scale bar on his graphs is 0.9 degree long.
Jan. 18: Comet to reach only magnitude +3?! Based on recent brightness estimates from Southern Hemisphere observers, Seiichi Yoshida, editor of Weekly Information about Bright Comets, has changed his magnitude formula for Comet PanSTARRS. His new predicted light curve (scroll down) has the comet peaking at only magnitude +3 in early March.
As we warned in print, the slightly hyperbolic orbit of PanSTARRS indicates that it's a fresh comet from the outer Oort Cloud being warmed by the Sun for the first time. Such comets have quite a history of brightening early with the promise of great things to come, and then weakening after a thin, virgin coating of volatiles on the nucleus evaporates off.
As of now the comet is 8th magnitude with a short dust tail. It's visible from the Southern Hemisphere low in the sky and will remain so until mid-February. Then it returns north.
Of course, anything could still happen. PanSTARRS seems to have reduced its rate of brightening when it was about 2.8 a.u. from the Sun. At perihelion on March 10th its distance from the Sun will be only 0.30 a.u., where the solar heating is nearly 100 times more intense. But plan on bringing those binoculars.
Jan. 12, 2013: Comet falling behind predictions? Now that Comet PanSTARRS is out of conjunction with the Sun for Southern Hemisphere observers, Jakub Cerny in the Czech Republic writes today on the comets-ml Yahoo Group mailing list:
Growing number of post-conjunction visual observations lead me to try to analyse pure visual light curve of this comet. You can see it at this location. The analysis is based on 155 visual observations [including 14 recent ones, post-conjunction].If this trend continues, the comet will peak at magnitude +1 or +2 in March, not 0 or brighter as formerly predicted.
You can see that there is noticeable brightening slowdown for this comet, that was expected for it as a dynamically new comet from the Oort Cloud.