[X] My Assistant

[scalbers]

Improved processed version of the unclipped image. This now shows M4 (faintly) for comparison.
[attachment=31536:lastimg_C3_v2.jpg]

Indeed M4 could be a reference to do some rough areal integration measurements. At least we know it's much brighter than M4. With some quick rough measurements and back of the envelope calculations I get somewhere around 2.8 magnitude for the more condensed region of the comet (including 6x9 pixels). I assumed brightness changes are scaled linearly.

[scalbers]

Here is the ground based image I mentioned earlier from Slovakia that may possibly show ISON the day before perihelion. Hard to be sure though it seems pretty high resolution with a scale of each pixel being about 1 arc minute. The object is smeared over about a 2 arc minute diameter, unless hot pixels are being spread by JPEG artifacts. Magnitude of ISON at this time would be about -0.5.

https://www.facebook.com/photo.php?fbid=262...e=1&theater

If this was from a clear mountain location then maybe it's just possible, with minimal aureole around the sun. This can be compared with an estimated sky brightness assuming simple Rayleigh scattering, for which I get about -4.5 magnitudes per square arc minute (assuming a modest elevation above sea level). Thus it would have about 2% contrast if it's only a square arcmin, and it seems brighter than that in the image.

[Mongo]

posted on comets-ml by srosenow_98 at 1:32

C/1962 C1 Seki-Lines vs C/2012 S1 ISON - Why ISON may dazzle us

Hi, folks! My name is Steve Rosenow, an avid astrophotographer. As I type this, I am left to wonder what exactly NASA scientists, as well as the general media, were thinking when they declared Comet C/2012 S1 ISON dead after yesterday morning's harrowing passage through perihelion. I am still left wondering why many are still deeming ISON dead, despite clear evidence stating otherwise.

Allow me to explain.

Over the last 24 hours, I have gleaned a lot of new information - particularly that of two prior sungrazing comets that performed almost exactly identical to what ISON is doing now - those being Comet C/1962 C1 Seki-Lines, and Comet C/2011 W3 Lovejoy. Judging from my readings into Comet C/1962 C1 Seki-Lines, and Comet C/2011 W3 Lovejoy, I suspect we're in for a nearly-identical performance.

For one, C/2011 W3 passed only 80,000 km above the surface of the sun. It was also very much smaller than the nucleus of C/2012 S1 ISON, at 1/9th the size. At last estimate, Comet ISON's nucleus was estimated to be at least the size of Manhattan - at the very minimum a few miles across. Lovejoy's nucleus on the other hand, was in the range of anywhere between 500-1000 feet at maximum. The speed in which ISON was traveling through perihelion, leads me to believe that it is really quite possible for a pretty considerable chunk of ISON to remain relatively intact - and even possibly completely intact. I say this because ISON also traveled through perihelion at a much greater distance from the sun itself, much greater than that of Lovejoy.

Second, the speed. While Lovejoy traveled faster (estimated to be around 333 miles per second, or 2% of the speed of light), ISON's speed was only marginally slower - at about 1/6th slower than Lovejoy - and that slower speed is only attributed to the separation distance between the surface of the sun and ISON's nucleus. By comparison and separation distance, it would appear that ISON and Lovejoy - if traveling at the same distance from the sun - would have been traveling at nearly the same speed. Due to that theory, I believe it stands as much a greater chance of survival (at least for now), as did Lovejoy did in 2011.

Finally, in 1962, Comet Seki-Lines (discovered by a pair of astronomers, one from Japan and one from the state of Arizona), performed identically to how ISON is doing now. At perihelion, it was expected to become a mag. -7 naked eye daytime object. Instead, it became invisible at perihelion only to emerge in the sky a few days later as a naked eye object as bright as Jupiter - which is the second-brightest object in the night sky right behind the star Sirius. It also sprouted a tail about 20 degrees long. To put that in mind, 20 degrees in the night sky, is about twice the width of a human fist held at arm's length.

Time will tell, but I think we have ourselves a definite survivor here!

posted on comets-ml by Roger N Clark at 5:57

Science and comets

There has been a lot of discussion on this list about science and the scientific method.

As a professional planetary scientist with well over 200 peer reviewed publications on objects throughout the Solar System, let me give my perspective on the last few weeks on this list.

I only recently joined this list having just heard about it and was told other professionals were on the list.

In my opinion, some of the activities on this list sold as the scientific method were anything but.

The scientific method is not putting out prediction after prediction of disintegration based on statistical data of other comets or strange data points. Statistical correlation is not causation. This is one of the largest errors scientists succumb to that I have observed in my nearly 40 years in this business. That and getting an idea and using selective data to prove their idea. Then holding onto an idea regardless of evidence.

The scientific method is methodical evaluation of multiple ideas and letting the data lead to the answer. It is not a supposition where data is selected to promote that supposition.

For example, as the comet faded as it got close to the sun, it was predicted that the dust in the tail would be vaporized and the comet would fade. Yet some ignored this and took the fading as destruction of the comet. This despite historical evidence that other comets have done this, as well as the prediction of vaporization of dust.

In a recent email, Jacub said: "I don’t think this is good and the new wave of "comet has survived" but without addition "but almost entirely destroyed" making broad public thinks that they will see a naked eye comet soon. We should be more careful in what we are saying to lay people."

What evidence for "almost entirely destroyed?" I certainly do not see that. The comet continued to brighten and the tail developed just as predicted. The comet is recovering from its close approach to the sun, and how well it develops a new tail and what kind of show it will put on is unknown. The press should not be told the comet was "almost entirely destroyed," as that is not supported by evidence; it is merely conjecture.

In the weeks leading up to encounter, ISON brightened and faded multiple times on a short term basis. usually after each fading, the prediction of the comet's demise was spouted again.

The press ate it up.

Good science would have pointed out the various models for the comet, rather than stating the comet is breaking up/disintegrating, etc. Bad science is yelling the comet is dead every time it fades a little.

Comets are dynamic objects whose activity varies not only with solar distance, but with composition of ices and dust, and the brightness is further complicated by rotation with jetting regions rotating in and out of sunlight. Then general trends changed with phase angle effects. Phase angle effects can darken with increasing phase (e.g. above 90 degrees), stay about the same, or brighten, all dependent on the grain size distribution of the particles in the cloud.

So, proclaiming that the comet is nearly entirely destroyed has little credible evidence at this point. The comet is now pulling away from the sun, so it will fade. But it will also likely show variable activity brightening and fading as outbursts occur and wane.

Only when the nucleus is observed to be split into multiple pieces will there be real evidence for breakup. Brightness variability is not such evidence.

Roger Clark

posted on comets-ml by JAMES at 6:48

Re: ison tail pointing wrong way

The dust tail of the comet is now divided into two parts," explains Hermann Böhnhardt from the Max Planck Institute for Solar System Research. According to Böhnhardt, the part of the tail that is pointing towards the sun consists of dust particles, which were released significantly before the comet's Perihelion passage i.e. prior to reaching the closest point to the sun.

The other part, however, appears to contain more recent material: It was released when ISON passed the sun and suggests that at least part of the nucleus still existed and was active at that time.

The Max Planck researchers base their assessment on computer simulations in which they model the shape of the dust tail. "If we assume in our calculations that the comet has emitted dust at Perihelion, we can reproduce the current images quite well," says Böhnhardt.

[Paolo]

we have a survivor, no doubt, but fading rapidly. just compare how faint it is now as it exists the C3 FOV compared to when it entered it

Attached thumbnail(s)

 

[scalbers]

Perhaps a bit OT, but if you actually want to see a comet now, the current Lovejoy is a naked eye comet at about peak visibility in the pre-dawn sky.

[Mongo]

I have to say that I am worried that there is still no sign of ISON showing a brightening nucleus. Although it took several days after perihelion for C/1962 Seki-Lines to suddenly reappear, so all hope is not yet lost.

I found the linked ARXIV paper that lists several non-detections of Seki-Lines near perihelion, and their limiting magnitudes:

Mar 30 -- 1.99 days before perihelion -- comet not seen, dimmer than -0.7, expected to be -2.2
Mar 31 -- 1.16 days before perihelion -- comet not seen, dimmer than -1.1, expected to be -2.5
Apr 01 -- 0.16 days before perihelion -- comet not seen, dimmer than -1.9, expected to be -2.8

Seki-Lines was expected to reach magnitude -7 right at perihelion, but was not seen. It reappeared at magnitude -2.5 on April 3rd.

So it's still a possiblity that ISON will reactivate and brighten, but if its nucleus does not reappear on images sometime today, the odds of it re-brightening appear to be low.

[dilo]

Comparison between SOHO/Lasco and the two Stereo views, almost same time but very different positions!

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[Mongo]

What do you guys make of this?

pwr_photo posted this on comets-ml earlier today:

Any clues what the little dot in C3's 15:42 photo close to where ISON's core could be? The (very) little dot is not there in the 14:54 and 15:54 photos but it's clearly in the 15:42 photo. Too much of a coincidence having it there.... May be it's just an issue related with the 1 Mpixel resolution of the camera?

So I combined the three most recent C3 images that I have access to, time-stamped as (left to right) 14:18 UT, 14:42 UT and 16:06 UT.

There is nothing visible ahead of the ISON dust cloud in the 14:18 image, while something does appear in the 14:42 image. A speck at the same location (relative to the dust cloud) is even brighter in the 16:06 image. Could it be the ISON nucleus finally coming to life, or is it just a coincidence?

Once the next C3 image is online, this should be settled.

Attached thumbnail(s)

 

[scalbers]

Comparison between SOHO/Lasco and the two Stereo views, almost same time but very different positions!

Looks like fan shape being seen from differing perpectives. One can probably make a 3D model of this.

[fredk]

Could it be the ISON nucleus finally coming to life, or is it just a coincidence?

The latter. The newer images (up to 19:18) show nothing. These images are full of cosmic ray hits.

[Mongo]

The latter. The newer images (up to 19:18) show nothing. These images are full of cosmic ray hits.

Where are you finding these images? The latest one I see in the archives I've checked is the 16:06 image.

[scalbers]

This site sometimes has more recent ones...

http://lasco-www.nrl.navy.mil/java/lastC3.html

Here is a magnitude plot by Jakob Cerney at comets-ml, dimming steadily.

http://www.kommet.cz/datas/users/ison-failed-4_1.png

I put this new magnitude relationship into my ephemeris here, though if it gets more diffuse it would be harder to spot than suggested by the magnitude values:

http://laps.noaa.gov/albers/ast/eph/ISON.2012S1.co.html

[Jaro_in_Montreal]

Please excuse my ignorance....
....but the fact that SDO didn't see the comet break up seems interesting to me:
SDO typically sees ONLY oxygen glowing from sun-grazing comets.
ISON's invisibility suggests that the ice in it's nucleus wasn't water or CO2 or CO, but instead ammonia or nitrogen (no oxygen).
Any other possibilities ?
Thanks.

[djellison]

ISON's invisibility suggests that the ice in it's nucleus wasn't water or CO2 or CO, but instead ammonia or nitrogen (no oxygen).
Any other possibilities ?
Thanks.

Yes - that it was too small to be observed at all in SDO. Some exotic nucleus composition would fly in the face of all the ground and space based observations that preceeded it's no-show in SDO data.

[Jaro_in_Montreal]

Yes - that it was too small to be observed at all in SDO. Some exotic nucleus composition would fly in the face of all the ground and space based observations that preceeded it's no-show in SDO data.

The commentary I heard was that ISON probably broke up into small pieces as it looped around the Sun.
Such a break up would seem to imply an INCREASE in the release of volatiles, not a decrease.