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steveward53
Pooh-Bah


Reged: 05/14/12

Loc: Newmarket,UK
Re: Comet ISON - Cooked well done? new [Re: SteveRosenow]
      #6222894 - 11/29/13 07:03 AM

On a lighter note ...

http://imgs.xkcd.com/comics/oort_cloud.png


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Mirzam
Post Laureate
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Reged: 04/01/08

Loc: Lovettsville, VA
Re: Comet ISON - Cooked well done? new [Re: steveward53]
      #6222935 - 11/29/13 07:59 AM

I am no expert on comets, but if a breakup into a number of large pieces occurred would not a large percentage of the fresh surface area be very cold, and thus, require a period (minutes, hours?) of heating to regain a high level of activity? Could something like this account for the sharply reduced activity near perihelion? Also, would large fragments spread out along the orbit more slowly than smaller fragments? In other words, can we infer anything about the size of remaining fragments from the expansion rate of the newly formed coma produced by multiple sources within a cloud like structure?

JimC

Liked the cartoon BTW!

Edited by Mirzam (11/29/13 08:02 AM)


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Dave M
Postmaster
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Reged: 08/03/04

Loc: Ohio
Re: Comet ISON - Cooked well done? new [Re: Mirzam]
      #6222966 - 11/29/13 08:33 AM Attachment (28 downloads)

"Courtesy of SOHO/[instrument] consortium. SOHO is a project of international cooperation between ESA and NASA." Link

C3 09:22


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Comet ISON - Cooked well done? new [Re: Mirzam]
      #6222968 - 11/29/13 08:37 AM

Tonk bear me to the punch; I feel the combination of velocity vectors and acceleration (including change of direction) to be largely responsible for the perihelion dimming. The nucleus is effectively stripped of its coma, or the nucleus outruns the coma.

And it's the coma we see, *not the nucleus*. (Even what we call the nucleus in high resolution images is really the pseudo nucleus, or brightest inner coma.) Even if albedo were 100%, a 2km body would be awfully dim at 1AU from us, even when near the Sun. (And near the Sun it has to compete with the quite bright corona.)

Therefore it takes time for the coma to build up again, and for a 'fresh' tail to develop.


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SteveRosenow
professor emeritus
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Reged: 07/10/12

Loc: Shelton, Washington
Re: Comet ISON - Cooked well done? new [Re: GlennLeDrew]
      #6222978 - 11/29/13 08:50 AM

12:30



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Jure Atanackov
super member


Reged: 05/04/10

Re: Comet ISON - Cooked well done? new [Re: SteveRosenow]
      #6222999 - 11/29/13 09:01 AM

At this time the comet still looks fainter than magnitude +1. But it does appear something made it through ...

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Mirzam
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Reged: 04/01/08

Loc: Lovettsville, VA
Re: Comet ISON - Cooked well done? new [Re: Jure Atanackov]
      #6223005 - 11/29/13 09:08 AM

Not sure why you say this? It looks to be a couple magnitudes brighter than Antares in the SOHO images? (Antares is +1.09 avg).

JimC


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Jure Atanackov
super member


Reged: 05/04/10

Re: Comet ISON - Cooked well done? new [Re: Mirzam]
      #6223013 - 11/29/13 09:14 AM

Antares is causing a bit of blooming, the comet at the moment is not.

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SteveRosenow
professor emeritus
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Reged: 07/10/12

Loc: Shelton, Washington
Re: Comet ISON - Cooked well done? new [Re: Jure Atanackov]
      #6223016 - 11/29/13 09:18 AM

Quote:

Antares is causing a bit of blooming, the comet at the moment is not.




Bear in mind, that Antares is a bright pinpoint of light.

The newly-developed coma from ISON (or its remnant) is a little more spread out.


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Tonk
Postmaster
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Reged: 08/19/04

Loc: Leeds, UK, 54N
Re: Comet ISON - Cooked well done? new [Re: SteveRosenow]
      #6223025 - 11/29/13 09:23 AM

Quote:

Not sure why you say this? It looks to be a couple magnitudes brighter than Antares in the SOHO images? (Antares is +1.09 avg).




Because there is a well established calibrated method to measure brightness of objects in SOHO images based on the integration of the blooming spikes - this method is reliable. You cannot go on how Antares "looks" because its image is saturated - its actually much brighter than the image shows and that can be worked out by adding in a factor for the blooming spikes

Antares is brighter than the comet


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Jure Atanackov
super member


Reged: 05/04/10

Re: Comet ISON - Cooked well done? new [Re: SteveRosenow]
      #6223029 - 11/29/13 09:24 AM

True. But to settle that we'd have to actually do some photometry I was looking at this from a visual observer's point of view. I actually planned to try and see the comet around noon today, but if it is not bright and really condensed (=blooming) it's pointless.
CS!Jure


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SteveRosenow
professor emeritus
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Reged: 07/10/12

Loc: Shelton, Washington
Re: Comet ISON - Cooked well done? new [Re: Jure Atanackov]
      #6223036 - 11/29/13 09:32 AM Attachment (32 downloads)

Even the alternative view of the LASCO C3 shows some brightening.

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Jure Atanackov
super member


Reged: 05/04/10

Re: Comet ISON - Cooked well done? new [Re: SteveRosenow]
      #6223049 - 11/29/13 09:42 AM

The current situation can still be (IMHO) well described with complete disruption of the nucleus into a cloud of large 'boulders'. The comet looked fainter at perihelion and now appears brighter. There are possibly 3 factors contributing to that:

1. At perihelion the debris cloud becomes more extended. The particles at perihelion have a higher velocity than before and after perihelion. Thus some of the particles are way ahead, some just passing perihelion and some lagging behind. After perihelion all particles catch up and the cloud condenses.

2. We're viewing the comet right into its tail.

3. The phase angle is now quite large, so forward scattering may be playing a significant role in this brightening. From Marcus' paper on fwd scattering brightness increase, there could be a 1 magnitude brightness surge today.


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Dave M
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Reged: 08/03/04

Loc: Ohio
Re: Comet ISON - Cooked well done? new [Re: Jure Atanackov]
      #6223099 - 11/29/13 10:18 AM

Spaceweather.com has now reseurrected ISON from the dead and says it is rapidly brightening.
http://spaceweather.com/
The coronagraph movie is awesome to watch.


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square_peg
Postmaster
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Reged: 03/26/04

Loc: Maple Valley, WA
Re: Comet ISON - Cooked well done? new [Re: Dave M]
      #6223124 - 11/29/13 10:37 AM

Thanks for the link, Dave. Great movie.

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djeber2
Pooh-Bah
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Reged: 07/02/04

Loc: Cloudy Midwest
Re: Comet ISON - Cooked well done? new [Re: Dave M]
      #6223133 - 11/29/13 10:41 AM

Quote:

Spaceweather.com has now reseurrected ISON from the dead and says it is rapidly brightening.
http://spaceweather.com/
The coronagraph movie is awesome to watch.



Sounds like good news.


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kevin M13
sage


Reged: 03/07/09

Loc: Upstate NY
Re: Comet ISON - Cooked well done? new [Re: djeber2]
      #6223170 - 11/29/13 11:02 AM

That is a cool clip !

Kevin


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MawkHawk
sage
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Reged: 08/23/09

Loc: SE Michigan, USA
Re: Comet ISON - Cooked well done? new [Re: kevin M13]
      #6223182 - 11/29/13 11:12 AM

That is very cool! Did ISON's course change, does anyone know?

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SteveRosenow
professor emeritus
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Reged: 07/10/12

Loc: Shelton, Washington
Re: Comet ISON - Cooked well done? new [Re: MawkHawk]
      #6223218 - 11/29/13 11:28 AM

Quote:

That is very cool! Did ISON's course change, does anyone know?




Per Comet ISON's Observing Campaign, no.

Their last tweet:

"Comet #ISON's orbit will NOT have changed appreciably during perihelion. Perhaps a *tiny* nudge but absolutely nothing to worry about."


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JayinUT
I'm not Sleepy
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Reged: 09/19/08

Loc: Utah
Re: Comet ISON - Cooked well done? new [Re: MawkHawk]
      #6223229 - 11/29/13 11:34 AM

Karl Battams on his blog said no, orbit hasn't change or if it has, only a nudge. He also states that the nucleus, if there is one, has loss a lot of mass as a result of its flyby. Edit: Got beat to it while reading and typing, cool.

See Sungrazers Tweets at this link if you want.

Edited by JayinUT (11/29/13 11:35 AM)


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