Star*Points for March, 2013
Comet PanSTARRS is Coming!

The astronomical star for this month is a hairy star, or comet.  The name is C/2011 L4 (PanSTARRS). Will 
it be visible to the naked eye, and if so where will it appear and when?  Will there be public viewing 
sessions with volunteers to help point it out?  Keep reading for answers to these questions, and more.

Modern comet names reflect the time of discovery as well as the names of the discoverers.   For 
example, Comet Hale-Bopp (C/1995 O1), or the great comet of 1997, was named after its co-
discoverers, Alan Hale and Thomas Bopp.  They were observing independently from New Mexico and 
Arizona, respectively, when they discovered the comet in the summer of 1995  

Comet PanSTARRS was discovered by an automated telescope in Hawaii that is part of the Panoramic 
Survey Telescope & Rapid Response System, or Pan-STARRS.  The objective of the survey is "to discover 
and characterize Earth-approaching objects, both asteroids & comets, that might pose a danger to our 
planet."  The telescope sweeps the sky automatically, taking images and looking for new objects.

The official designation of Comet PanSTARRS is C/2011 L4.  The letter C means comet and, in particular, 
one that is non-periodic. Non-periodic comets are those that have not been previously observed and 
aren't expected to return.   On the other hand, the letter P is used for denoting periodic comets, such as 
Halley's that returns every 76 years.  

The next value is the year of discovery, 2011, and finally the month and order of discover.  L4 indicates 
that PanSTARRS was the fourth comet discovered in the latter half of June.  

It wasn't the first comet to be discovered by Pan-STARRS. The survey discovered periodic comet P/2010 
T2.  It has also discovered two supernovas and two asteroids.  One of the latter is a Near Earth Asteroid 
(NEA) that has a slight possibility of colliding with the earth in 2098.

At the time of its discovery, Comet PanSTARRS was 759 million miles from the sun. By comparison 
Jupiter's average distance from the sun is only 483 million.  Based on its orbital characteristics, 
astronomers believe PanSTARRS is now making its first trip to the inner solar system.  Such fresh comets 
often brighten quickly as fresh ices sublimate, due to the increasing solar radiation as the comet draws 
nearer, forming a cloud around the nucleus, known as the coma.  Sometimes, however, new comets can 
fade just as quickly as they brighten.

Early expectations for Comet PanSTARRS were calling for it to achieve brightness similar to naked eye 
planets.  But as the new year opened, its brightening began to slow, and thus expectations were 
reduced.  Lately, it's been observed to be steadily brightening again such that it could reach naked eye 
brightness similar to the stars of the Big Dipper.

During the inbound trip, PanSTARRS bided its time in the southern sky, never rising above the horizon 
for Maryland viewers.  In March it finally makes its way to northern skies.  On May 5 the comet is at its 
closest point to earth.  At that time it will slightly farther away from us than the sun.  

Then, on March 10, PanStarrs reaches its closest point to the sun, known as perihelion.  By that time it 
may have begun making nightly appearances very low in our western sky in bright twilight after sunset.

The best time to see Comet PanSTARRS is starting 30 or 45 minutes after sunset.  This would be the 
period approximately between 6:45 and 7:00 p.m EST or, starting when the daylight time begins on 
March 10, between 7:45 and 8:00 p.m. EDT.  Each day the comet will be a little higher, where the sky 
will be darker, and will hang around longer before quickly setting.

You need a low unobstructed horizon to the west because the comet will be very low.  On the night of 
March 12, the comet will be low in the west just to the left of a crescent moon.  Finder charts can easily 
be found online by Googling Comet C/2011 L4 (PanSTARRS).

Public observing events will be held around the county on the night of Monday, March 11 at each 
branch of the Carroll County Public Library system.  Weather permitting, members of the Westminster 
Astronomical Society will be on hand at each site to help point out the comet between 7 and 9 p.m. EDT.  
They are recommending guests to bring their own binoculars and practice so that they can keep 
following the comet on subsequent nights.

The observing sessions will be held at the Eldersburg, Finksburg, Mt. Airy, North Carroll, Taneytown, and 
Westminster branches.  For more information about the event, check the library calendar site 
(http://library.carr.org/programs/calendar.asp).