Comet ISON Update


Article by Suzy Webb.

These last couple of weeks have been a real roller coaster ride with comet ISON as it’s certainly been behaving with some attitude and pretty much doing the exact opposite of what’s expected. The month of November started with a very slow climb in brightness. In fact, just three weeks ago comet C/2013 R1 Lovejoy was outperforming ISON and stealing the show reaching magnitude 5.5. ISON’s nucleus at this stage wasn’t rotating so only one side was facing the sun. There was hope that once it got closer to the sun it would reveal its other side causing more dust to appear (we want lots of dust for a nice tail!). Observations were showing it to have a lot of gas, hence the blue/green colour.

Come November 12th, ISON was rapidly racing below our horizon. When comets get closer to the sun, the faster they travel. At the time, it was barely visible through even a 12” telescope from a dark site, sitting around magnitude 8 and just 16 days off perihelion (closest approach to the Sun).
Then all of a sudden on November 13th, something unexpected happened. It’s very unusual for a comet to have such a quick and sharp rise in brightness- it brightened to magnitude 5. Then on November 21st it brightened further to magnitude 3.7, where it was easily observed in binoculars. On the 21st, at 4am here in Brisbane, ISON was sitting just 10 degrees above my horizon in a brightening dawn sky. But despite this, and a bright moon in the way, it was still an easy catch in binoculars! It was such a thrill for those who had clear skies to just catch it just in time before it disappeared to the northern hemisphere.

The APOD image above is when ISON was in outburst. Very few pre-perihelion widefield nightscape images were shared out as there was such a small window of opportunity and the weather wasn’t co-operating for many.

Then, uh-oh! Photometry observations were now coming in thick and fast about a possible fragmentation or disintegration event causing the brightness outburst. The “angel wings” noted on images fed this further. Then, within the same week, it started to dim again. This was not looking good a week off its November 28th perihelion (29th for us Aussies). Karl Battams who operates the NASA funded Sungrazing Comets Project, summed it by saying, “It’s either fine, completely broken up or somewhere in between.” Everyone was left scratching their heads. On November 28th, there was much relief when the brightness picked up again, indicating that perhaps it’s nucleus is still intact. Time will tell. Perihelion is just a few hours away. So now we wait and see, if it survives its close encounter with the Sun.....

On a final note, and now, just a few short hours before perihelion, I leave you with words from Astroblogger, Ian Musgrave: “Now on the last leg of its long journey, which began around a million years ago in the Oort cloud at the edge of the solar system, in a few short hours it will skim around a solar diameter from the surface of the sun, being exposed to almost unimaginable heat which will vaporise the very dust on its surface.”

UPDATE 8am Friday:

Well it seems "that unimaginable heat which will vaporise the very dust on its surface" took out the whole comet all together! No visible fragments can be seen at this stage. No nucleus of any form is visible and the the tail's appearance resembles one of a debris tail. They don't hold much hope for it. So it's not looking good at all for this morning's perihelion encounter.

Carl Battams said they were going to give it another couple more hours before they start writing ISON's obituary and that was an hour and a half ago.

C. Alex Young said that there will be no meteor shower either, as ISON will not be making its closest approach to Earth on the 26th December for that to happen.

This was a very special comet of interest.

It's the first time in observable history that a first time Oort Cloud comet was to graze the Sun (Sungrazer). There was much science to be learned from this event which would've helped us further understand the formation of our solar system. This is why there was a global observing campaign on ISON to watch it closely.

Phil Plait remaining optimistic, said that hopefully we will still be able to get some information from the debris.

UPDATE Tuesday 7am:

The comet definitely looks to have broken up. Click the image below to watch a movie of the comet approaching the Sun and then breaking up as it comes around the other side.

It also takes you to the IceInSpace Facebook page where there's some FAQ's courtesy Karl Battam's blog about what's left of Comet ISON.


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