Comet Ison It

December 1, 2013 by staff 

Comet Ison It, Or… “That time I was right, then wrong, then probably right again like I was in the first place, more or less.”

The other day I wrote up a synopsis of the life and possible death of comet C/2012 S1 (ISON). Karl Battams, who runs the SungrazerComets Twitter feed and the Comet ISON Observing Campaign page, has an excellent summary of what we know so far (with a couple of very cool animations, too). The bottom line is that it’s been one surprise after another, with it getting bright, then dim, then bright again, then dim.

But, as we get more images of the comet as it heads away from the Sun, its ultimate fate is perhaps a little easier to see. The NASA / ESA spacecraft SOHO has been observing the comet since it entered its field of view on Nov. 28, and has told an interesting if somewhat head-scratchy tale. The solid nucleus of the comet started out about two kilometers wide, and got very bright. It faded rapidly as it approached the Sun, pretty much the opposite of what you might expect. But then it got bright again after it rounded the Sun, though not nearly as bright as before. And now it appears to be fading without stop.

Here’s a video I put together showing the comet starting on Nov. 28 at 07:00 UTC (02:00 EST), and ending 44 hours later on Nov. 30 at 04:00 (Nov. 29 at 11:00 p.m. EST):

You can see the comet head was so bright at the beginning it was saturating the SOHO detector, but then faded fast (I wrote a brief explanation of what you see in SOHO images in an earlier post). The other thing to note is that now, days later, the comet has faded substantially; there is no nucleus to be seen, and we can even see stars right through the comet (the image at the top of this post was taken on Nov. 30 at 20:42 UTC, and makes that clear; ISON is on the upper right and is now pretty well dispersed).

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