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Friday, November 29, 2013


Comet C/2012 S1 ISON stays on track (29 November UT)

Comet C/2012 S1 ISON seen in the SOHO LASCO C3 instrument at 06:18 UT 29 November. Stars indicated for comparison with chart. Click to embiggenChart of the predicted position of ISON at 06:18 UT 29 November.Click to embiggen

In the wake of the dramatic breakup and revival of comet ISON as it rounded the Sun, once again there has been speculation that it is significantly off track.

Here I show one of the latest SOHO images together with the predicted position of ISON at the same time, using old orbit parameters. ISON is exactly where it should be, between Chi Ophiuchus and the dim star TYC-6210-254-1. Measuring their positions I find the present position of ISON is within 6" of teh predicted poition, well within the measurement error from the images.

Pre-perihelion track positions diagram and predictions are here.

Note the broad fan shape of comet ISON at the moment, comet ISON seems to be reviving, a bit. But it is still not clear what we are seeing is a pile of gravel with attitude, or a substantial chunk of comet remnant. Karl Battams and the STEREO team think it likely that there is a substantial chunk of material, Terry Lovejoy and Jacub Cerny think it likely there is not.

All I can say is keep on watching, even if it is just gravel with attitude, it is still beautiful and we can still learn a lot.

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Ian -

Thanks for your detailed tracking of Ison.

Difficult to find solid tracking info, given its popularity and the amount of people watching it and making comments.

Maybe it ought to be called the "Resurrection" comet. A "cross" shape before it gets buried, then "death", then "resurrection."

Could you explain what that cross shape was just before Ison went behind the sun?

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