Nightscapes & Deep Sky Colors

Astrophotography Brian A. Morganti


Comet C/2011 L4 PanSTARRS


Comet C/2011 L4 (PANSTARRS) is a non-periodic comet discovered in June 2011 that became visible to the naked eye when it was near perihelion in March 2013.The comet was discovered using the Pan-STARRS telescope located near the summit of Haleakala, on the island of Maui in Hawaii.

Comet C/2011 L4 had an apparent magnitude of 19 when it was discovered in June 2011.  By early May 2012, the comet had brightened to magnitude 13.5, and could be seen visually when using a large amateur telescope from a dark site. As of October 2012, the coma (expanding tenuous dust atmosphere) was estimated to be about 120000 kilometers (75000 miles) in diameter.  The comet was spotted without optical aid on 7 February 2013 at a magnitude of ~6. Comet PANSTARRS was visible from both hemispheres in the first weeks of March, and passed closest to Earth on 5 March 2013 at a distance of 1.09 au.  It came to perihelion (closest approach to the Sun) on 10 March 2013.  Original estimates predicted the comet would brighten to roughly apparent magnitude 0 (roughly the brightness of Alpha Centauri A or Vega).  An estimate in October 2012 predicted the comet might brighten to magnitude -4 (roughly equivalent to Venus).  In January 2013 there was a noticeable brightening slowdown that suggested the comet may only brighten to magnitude +1.   During February the brightness curve showed a further slowdown suggesting a perihelion magnitude of around +2.

However, a study using the secular light curve indicates that the comet had a "slowdown event" when it was 3.6 au from the Sun at a magnitude 5.6.  The brightness increase rate decreased and the estimated magnitude at perihelion was predicted as +3.5.  Comet Halley would be magnitude −1.0 at the same perihelion distance. The same study concluded that the comet is very young and belongs to the class of "baby comets".

When the comet reached perihelion in March 2013, the actual peak magnitude turned out to be around +1,  as estimated by various observers all over the world. However, the low altitude of the comet over the horizon made these estimates difficult and subject to significant uncertainties, both because of the lack of suitable reference stars in the area and the need for differential atmospheric extinction corrections.  As of mid March 2013, due the brightness of twilight and low elevation in the sky, the comet is best seen in binoculars about 40 minutes after sunset.

Comet C/2011 L4 probably took millions of years to come from the Oort cloud.  After leaving the planetary region of the Solar System, the post-perihelion orbital period (epoch 2050) is estimated to be roughly 106000 years!

All images below were taken with a Canon 5D MII with a Canon 70-200mm f2.8L lens mounted on a tripod and processed in Photoshop CS6. 

Wednesday - March 13, 2013

  8:00pm EDT - 78mm @ f2.8 - 1 second exposure - ISO800

8:09pm EDT - 200mm @ f2.8 - 3 second exposure - ISO 800

8:14pm EDT - 400mm @ f5.6 - 2 second exposure - ISO 1600 


Thursday - March 14, 2013

7:59pm EDT - 70mm @ f2.8 - 1 second exposure - ISO 800

8:01pm EDT - 108mm @ f2.8 - 1 second exposure - ISO 800

8:14pm EDT - 160mm @ f5.6 w/2x extender attached - 6 second exposure - ISO 1600

8:16pm EDT - 200mm @ f5.6 w/2x extender attached - 8 second exposure + 1 stop exposure compensation - ISO 2500

8:17pm EDT - 200mm @ f5.6 w2x extender attached - 3 second exposure + 1 stop exposure compensation - ISO 2500

8:23pm EDT - 250mm @ f5.6 - 2 second exposure - ISO 12,800



Astrophotography  -  Nightscapes & Deep Sky Colors