ISON Image of the Week

A Surprisingly Well-behaved Comet (Aug 26, 2013)



Comet C/2012 S1 (ISON) is still a tricky object to spot in twilight skies, but French astronomer Jean-François Soulier has been successful in capturing several images of the comet over the past week or so.
It's hard to believe that it's only two weeks since comet ISON was recovered after being hidden by the Sun's glare for several weeks. Since then, observers have started to make more observations of the comet and report their findings, including the apparent brightness of the comet. In accordance with the latter, we have taken the measurements that have been submitted to the MPC and added them to our light-curve to show how ISON's current brightness is comparing to one particular model prediction of it's brightness behavior.

Since its recovery, there has been much speculation about ISON and how it may not be living up to expectations. Indeed, the term "dud" is starting to get used more than "Comet of the Century"! For the record, the CIOC does not support of condone the use of either of these terms. We have stated clearly that ISON's current brightness does not concern us, and indeed given the inherent unpredictability of comets, this one is actually being quite well-behaved and certainly very typical of an Oort Cloud comet!

We can offer absolutely no promise that ISON will shine bright in the night sky, but as of right now it is still alive and well and becoming increasingly visible. As a testament to this, French astronomer Jean-François Soulier has been successful at imaging comet ISON on a number of occasions, most recently just three days ago on August 23rd, 2013. In his latest image, opposite, we clearly see ISON's diffuse coma and faint tail trailing behind it. It's still not much to look at, but despite the recent concerns voiced by some astronomers, comet ISON is more or less looking exactly as we thought it would at this time.

By now, comet ISON has passed what we informally refer to as "the frost line", which means that it is now close enough to the Sun that its water ice -- it's main constituent -- is beginning to melt quite efficiently. It's as this water-ice melts that dust and gases trapped within the comet will be released in much greater quantities, leading to more material in the comet's coma and tail and a corresponding rise in its apparent brightness as sunlight illuminates this material. By the time ISON reaches its closest approach to Mars in October, we hope that it will be ready to put on a good show for the "Martian" spacecraft fleet that plan to attempt to observe it!

Every week this year we will put up a new image related to Comet C/2012 S1 (ISON). If you have a cool image you'd like us to consider, please send it to sungrazer@nrl.navy.mil, along with a description and any credits you would want applied. We'll contact you if we choose to use your image on the CIOC Website.

See our ISON Image of the Week Archives for earlier picks!