Comet ISON News and Links - 2013

Re: Comet ISON News and Links - 2013

Postby william-kowalczyk » Sun Sep 01, 2013 5:08 pm

Baby arrived on Aug 26th. We are in our period of adjustment, but I plan to start updating this thread again soon. Glad you like the info!
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Re: Comet ISON News and Links - 2013

Postby rene-gedaly » Sun Sep 01, 2013 6:40 pm

CONGRATS! to you, your wife, and baby K!
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Re: Comet ISON News and Links - 2013

Postby Guest » Sun Sep 01, 2013 10:30 pm

Congratulations Bill!

Thought I would start off by posting this to help out. :D

September provides your first peek at Comet ISON

http://astronomy.com/en/News-Observing/ ... 0ISON.aspx
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Re: Comet ISON News and Links - 2013

Postby william-kowalczyk » Fri Oct 18, 2013 11:00 am

I found this information useful for considering ISONs survivability as new size estimates are coming in:

... the Kreutz comets demonstrate the range of outcomes that may befall ISON. The smallest comets, consistently estimated to be <0.2 km in radius (e.g., MacQueen & St. Cyr
1991; Raymond et al. 1998; Sekanina 2003; Knight et al. 2010) succumb to sublimation driven mass loss prior to perihelion. Intermediate sized comets, 0.2–1.0 km in radius, are large enough to survive mass loss due to sublimation (Iseli et al. 2002; Sekanina 2003), but likely disrupt with no individual fragment sufficiently large to remain a viable comet significantly beyond perihelion. The largest comets (radius >1 km) easily survive mass loss due to sublimation alone and, even if they fragment, remain viable comets that will return on a subsequent perihelion passage.

Ref: Will Comet ISON (C/2012 S1) Survive Perihelion? Matthew M. Knight, Kevin J. Walsh

Though Comet ISON is not officially in the Kreutz group as a "dynamically new comet"; the Kreutz group survivability scale can be used to characterize ISON's chances of survival. Some more recent discussions about comet ISON have suggested that the comet is larger than previously estimated in the paper referenced above (0.1-2.0 km) and is now estimated to be in the 1-4 km range. There is also new data characterizing ISON rotation as very stable with its axis possibly aligned with its velocity vector. What does that mean? It means that there could be a side of comet ISON that has not yet seen the sun, and if so, that side may only be exposed post-perihelion. If the comet is on the larger side, sublimation influence on rotation will be less significant, and will increase the likelihood of this outcome. With updated size estimates, and considering the Kreutz survivability study, ISON might just be a great Christmas present for sky gazers, but then again it might not. Guess that's what makes comet chasing so much fun.
Last edited by william-kowalczyk on Fri Oct 18, 2013 3:02 pm, edited 2 times in total.
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Re: Comet ISON News and Links - 2013

Postby william-kowalczyk » Fri Oct 18, 2013 11:51 am

Further discussion on the rotation of comet ISON and how it was determined:

The nucleus’s density and rotation have a big say in what the tidal forces will do to ISON, Knight explained. He and Walsh ran simulations using likely densities and spin speeds for comets and found that, in most scenarios, ISON should survive. But survival is less likely if the nucleus is spinning very fast or prograde (i.e. forward toward the Sun). He puts the odds of survival above 50%, but jokes that the error bars on that estimate are “plus or minus 100%.”

The prediction is so uncertain in part because astronomers don’t know ISON’s spin. Hubble observations by Jian-Yang Li (Planetary Science Institute) and his colleagues indicate that the comet’s rotational axis is pointing at the Sun. The team detected a slight uptick in brightness that they interpret as a jet from the nucleus, and because this jet appears in all the images they took over 19 hours (and in ground-based observations over a two-month period), its stationary-ness suggests it’s quite near the nucleus’s pole. But no one’s seen changes associated with which way the nucleus is spinning.

The sunward-pointing pole is where ISON’s mystery deepens. The comet is following a parabolic orbit, meaning that, thus far, it’s basically been on a straight-shot trajectory toward the Sun. If it’s pointing only one hemisphere at the Sun, the other hasn’t been heated yet — and won’t be until maybe a week before perihelion, when the comet passes within Mercury’s orbit. When that happens, pristine surface material such as carbon dioxide ice could “sublimate like crazy,” releasing a lot of dust and causing an outburst, Li said. But he cautions that his team determined the pole’s location from only one set of observations in April, and the result could change with follow-up. Hubble observed ISON this week, so that follow-up is imminent.

Any outburst could wreak havoc with the nucleus's spin, making its survival even harder to predict.

Of course there’s always the wild card. Knight noted that comets in the solar system spontaneously disrupt for unknown reasons maybe 1% of the time. That’s beyond researchers’ ability to simulate.

In other words, we’ll have to wait and see what we’re dealt.


Ref: ISON’s Chances for Survival 50/50
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Re: Comet ISON News and Links - 2013

Postby kdrake » Thu Oct 24, 2013 6:46 am

The paper by Zdenek Sekanina "BRIGHTNESS AND ORBITAL MOTION PECULIARITIES OF COMET C/2012 S1 (ISON): COMPARISON WITH TWO VERY DIFFERENT COMETS" has been updated 10/22.
http://arxiv.org/pdf/1310.1980v3.pdf

Especially note in the STATUS UPDATE REPORT #2

"The comet continues to brighten at a sluggish rate, but has not run out of breath."

So are we to conclude the comet still has gas?? How profound. I'm really waiting to see what will be left of this little fuzzball after perihelion passage.

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Re: Comet ISON News and Links - 2013

Postby william-kowalczyk » Sun Nov 17, 2013 10:17 am

Great ISON pictures at Spaceweather.com Gallery

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Last edited by william-kowalczyk on Mon Nov 18, 2013 8:16 am, edited 13 times in total.
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Re: Comet ISON News and Links - 2013

Postby william-kowalczyk » Sun Nov 17, 2013 10:49 am

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Re: Comet ISON News and Links - 2013

Postby william-kowalczyk » Mon Nov 18, 2013 8:06 am

Posted in the netslyder by Michael Galindo:

Astronomer Phil Plait also has some good info on ISON:

http://www.slate.com/blogs/bad_astronomy/2013/11/17/ison_spectacular_pictures_of_a_gorgeous_comet.html
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