Physics Photo of the Week

March 28, 2014

Comet Lovejoy (C 2013 R1)
We had been hoping to get wonderful photos of Comet Ison this winter, but it did not survive the intense gravitational gradient when it passed close to the Sun.  It ended up in several small pieces that disappointed many comet viewers.  Comet Lovejoy came as a consolation "prize".  Terry Lovejoy, an Australian astronomer has discovered several comets that bear his name.  Perhaps his most famous comet was C/2011 W3, which was a brilliant sun-grazer.  Lovejoy's discovery of the 2013 comet is no small comet having reached naked eye brightness and almost naked eye visibility on the morning of Jan. 4 when I took this photo.  I took this photo with the college's CCD camera and a small lens.  The comet was too large for the long focal-length telescope - it would more than filled the field of view.

Comets are believed to be ancient remnants of the primordial solar system, most having spent billions of years in the outer reaches of the solar system called the Oort Cloud.  Every once in a while a comet is attracted by the gravity of the Sun and is drawn into sweep past the Sun and eventually return to the outer reaches of the Solar System.  Sometimes, comets interact with one of the large planets (Jupiter) and are "captured" by the planet to make a smaller periodic orbit completely about as long as the Jupiter-Sun distance.  Halley's comet is an example of a "captured" periodic comet that returns to the Sun every 76 years.  Other comets get flung further out of the Solar System by Jupiter's gravity.  In spite of the immense size of a comet's coma and tail (spanning millions of kilometers) the comet nucleus itself is rather small - often less than a kilometer in diameter.  Halley's nucleus was photographed by a spacecraft and found to be about 10 km across.  The comet consists of much volatile material that is blown away from the nucleus by the Sun's radiation pressure and the solar wind of charged particles.

Physics Photo of the Week has featured several other comets:  (Pan Starrs on March 15, 2013; Lulin on February 27, 2009; Comet Holmes on Dec. 7, 2007 and Nov. 1, 2007;   Other comets are featured in PPOW for Nov. 3, 2006 and Jan. 10, 2005).

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

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Observers are invited to submit digital photos to: