Updating my previous posts concerning the evolution of C/2011 L4, it is significant to note that no sightings of the comet seem to have been reported by southern hemisphere observers over the past 3 days as the comet moves ever deeper into the twilight. At last report PanSTARRS was 4th magnitude with a 1 degree tail, situated very low in the afterglow of dusk about 29 degrees almost due south of the Sun and visible only briefly in nautical twilight. Although continuing to brighten steadily, it seems ever more likely that the comet may become temporarily lost in twilight as its elongation from the Sun dwindles to just 15 degrees between now and March 10th. Just when it might be visually recoverable by northern hemisphere observers remains open to question and highly dependent on just how bright the comet becomes.
As of today selected photometric observations covering the past 6 weeks indicates a very steady but slow rise in the comet's brightness and development. An analysis of these data indicate that they can be very well represented by the formula:
m1 = 5.6 + 5 log(D) + 6.9 log®
as can be seen from the graph presented below.
These parameters, only very slightly differing from those presented earlier, but now even more certain, suggest a peak brightness of about +2.2 on or about March 10th, with a slow progressive 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, then PanSTARRS could put on a fairly respectable showing during late March and early April although heavily impacted by the inconvenient timing of the March full moon.
If PanSTARRS attains 2nd magnitude it should likewise 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 March is, of course, open to question. However, 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.