Long awaited, Comet PanSTARRS is on track to peak at only magnitude +2 or +3 in the March evening twilight for Northern Hemisphere skywatchers, not –1 as originally predicted.

Looking west in bright twilight. The comet symbols are probably exaggerated.

Bring binoculars to pick Comet PanSTARRS (C/2011 L4) out of the twilight low in the west. Don't expect it to look as obvious as this!

Sky & Telescope diagram

As we report in the print edition of S&T, Comet PanSTARRS (C/2011 L4) will emerge from the Sun's glare low in the western twilight in early and mid-March of 2013. But how bright will it be?

Fainter than we originally predicted.

More than a month ago, using brightness measurements coming from Southern Hemisphere observers, Seiichi Yoshida, editor of Weekly Information about Bright Comets, changed his magnitude formula for Comet PanSTARRS. His new predicted light curve (scroll down there) had the comet peaking at only magnitude +3 in early March.


Comet PanSTARRS was still only 19th magnitude at its discovery on June 6, 2011. These four discovery images, taken 20 minutes apart, show its motion against background stars. They were taken as part of the Pan-STARRS sky survey, which uses a dedicated 1.8-meter telescope on Hawaii's Mount Haleakala.

PS1 Science Consortium

In the month since then, with many more brightness estimates coming in from Southern Hemisphere observers, there has been little or no change in that new prediction.

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.

For further news as it develops, and recent images, bookmark our Updates on Comet PanSTARRS.


Looking west in bright twilight

Look west after sunset in early and mid-March for Comet PanSTARRS. Binoculars may be needed to pick it out of the sunset glow. Look too early and the sky will be too bright; too late and the comet will be too low. On the altitude scale at left, 10° is about the width of your fist held at arm's length.

This diagram is drawn for a viewer near 40° north latitude. If you're south of there, the comet will be a little higher above your horizon early in the month than shown here. North of 40°, it will be even lower in early March than shown here, but higher than here as it fades after midmonth.

Sky & Telescope diagram


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