The Great Comet of 2013 LINK
June 2013 Assessment of Comet ISON LINK
Photos of Comet ISON Potentially a Great Comet LINK
Comet Ison: daylight sighting of 'once in a lifetime' event possible LINK
Most of those writing about ISON admit that it could have been a great comet or a dud or something in between. Why? Because comets are like cats and just do there own thing even when we as humans think they are predictable. I like the analogy of comets being like teenagers having raised two, they are just unpredictable. Just when you think you figure out what is going on they surprise you!
Well yesterday, Comet ISON approached perihelion, which is the point an object comes closet to the Sun. As ISON approached the Sun, it seemingly disappeared. At that point many of the professional astronomers proclaimed that ISON had broken up and was no longer a comet. I was following this on NASA's Google Hangout and even posted such on a couple of message boards. While just like that teenager, or perhaps more like Fawke's, Dumbledore's phoenix by late yesterday afternoon early evening, ISON had come back to life!
Now, the experts are letting us know that basically they are not sure what happen to Comet ISON. Karl Battams, one of the leading astrophysicists on Comet ISON has a wonderful blog entry that explains what has happen so far. It can be found at this link. Karl on his twitter feed Sungrazer Comets has shared the following on Comet ISON. These are from his latest to oldest:
"Seems maybe something is still producing dust but whether it's a coherent nucleus or a dust ball, we don't know."
"One thing we can be certain of is that #ISON's nucleus (if there is one) will be significantly smaller now. Lot of mass will have been lost!"
"Comet #ISON's orbit will NOT have changed appreciably during perihelion. Perhaps a *tiny* nudge but absolutely nothing to worry about."
"For those asking, we really are not comfortable in speculating on naked eye visibility or not. Just give us a few more days! We're on it..."
Some may ask why scientists who know so much about comets and how they work could declare ISON dead, then a few hours latter, that something was left of it due to the images SOHO was providing? SOHO is the Solar and Heliospheric Observatory launched in 1995 to observe the Sun. Anyway, SOHO has a great observation of ISON going into perihelion and out of it. Here is a movie of that. However before I do that, one thing I have to say for Comet ISON. Whether we see it visually or not, whether it is considered just another comet, it has provided amateurs and those who followed it a wonderful opportunity to see how science works in action. That science is a quest for knowledge and as new things come up, scientists respond by trying to gather new information and make new knowledge based on more evidence. As astronomer and PhD Andy Puckett stated in a tweet, "Science is a process, and it takes time and effort to achieve accurate results." So lets enjoy the ride of Comet ISON, what we have to learn from it scientifically and personally, and if the opportunity presents itself again, to have a visual or telescopic view of it. Here is the link to that movie.
Here is ISON going in. The white circle is the sun, the darker blue smaller circle is another telescope.
Here is what is left of ISON emerging
Here is ISON remnants and a new tail developing.
Well Comet ISON did NOT survive perihelion and broke up. In the images above your seeing the dust cloud intensify and follow the gravitational path of the what had been the comet. To surmise what happen it is probably best to use these posts from the Yahoo Group on Comet's Mailing List found at this link:
to who is interested in science here without access to CBET telegrams,
here is a latest CBET 3731 about comet ISON.
Electronic Telegram No. 3731
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University;
20 Oxford St.; Cambridge, MA 02138; U.S.A.
Prepared using the Tamkin Foundation Computer Network
The comet's nucleus apparently disrupted near perihelion, with the
comet's head fading from perhaps a peak brightness of visual mag -2 some
hours before perihelion to well below mag +1 before perihelion. M.
Knight, Lowell Observatory, finds that the comet peaked around visual
mag -2.0 around Nov. 28.1 UT, adding that the brightest feature in the
coma of the comet faded steadily after perihelion from about mag 3.1 in
a 95"-radius aperture when the comet first appeared from behind the SOHO
coronagraph occulting disk on Nov. 28.92 to about mag 6.5 on Nov.
29.98. K. Battams, Naval Research Laboratory, writes that, based on the
most recent LASCO C3 images (Nov. 30.912 UT), there is no visible
nucleus or central condensation; what remains is very diffuse, largely
transparent to background stars, and fading; it appears that basically a
cloud of dust remains from the nucleus. S. Nakano, Sumoto, Japan,
writes that he measured the comet's total magnitude in a 27' photometric
aperture from the SOHO C3 camera images to be as follows: Nov. 29.383,
0.5; 29.755, 1.4; 30.013, 2.0; 30.496, 3.0; 30.883, 5.4.
Z. Sekanina, Jet Propulsion Laboratory, reports that, from the
position of the northeastern boundary of the comet's fan-shaped tail in
three images taken with the C3 coronagraph onboard the SOHO spacecraft
between 0.7 and 1.9 days after perihelion (Nov. 29.46 to 30.66 UT), he
finds that the comet's production of dust terminated about 3 hours
before perihelion. Although this result is preliminary, it is unlikely
to be significantly in error, because the position angles of a
perihelion emission are off in the three images by 14-22 deg, and those
of post-perihelion emissions still more. The peak radiation-pressure
accelerations derived from the tail boundary's angular lengths
(estimated at 1.8-2.5 deg) are about 0.1-0.2 the solar gravitational
acceleration, implying the presence of micron-sized particles. The
estimated time of terminated activity is consistent with the absence of
any feature that could be interpreted as a condensation around an active
nucleus in the 20 or so images taken with the C2 coronagraph on Nov.
28.8-29.0 UT (0.8 to 5.4 hr after perihelion) and with the appearance of
a very sharp tip (replacing a rounded head) at the comet's sunward end
in the C2 images starting about 4 hr before perihelion and continuing
until its disappearance behind the occulting disc around Nov. 28.74 UT
(or some 50 minutes before perihelion). The time of terminated activity
is here interpreted as the end of nuclear fragmentation, a process that
is likely to have begun shortly before a sudden surge of brightness that
peaked nearly 12 hr prior to perihelion. Fine dust particles released
before perihelion moved in hyperbolic orbits with perihelion distances
greater than is the comet's, thus helping some of them survive. The
post-perihelion tail's southern, sunward-pointing boundary consists of
dust ejected during the pre-perihelion brightening. However, the
streamer of massive grains ejected at extremely large heliocentric
distances, so prominently seen trailing the nucleus along the orbit
before perihelion (cf.CBET 3722), completely disappeared. The dust
located inside the fan, between both boundaries, was released in
intervening times, mostly during the last two days before perihelion.
The strong forward-scattering effect (phase angles near 120-130 deg) has
tempered the rate of post-perihelion fading of the comet, but the
merciless inverse-square power law of increasing heliocentric distance
is necessarily the dominant factor in the comet's forthcoming gradual
H. Boehnhardt, J. B. Vincent, C. Chifu, B. Inhester, N. Oklay, B.
Podlipnik, C. Snodgrass, and C. Tubiana, Max Planck Institute for Solar
System Research, Katlenburg-Lindau, reports that two diffuse tail
structures were analyzed in post-perihelion images obtained by the
LASCO-C3 corongraph onboard the SOHO spacecraft between Nov. 29.60 and
29.81 UT. The southward tail extended toward p.a. about 167 deg to
about 0.4 deg distance from the central brightness peak. The eastward
tail had an approximate position angle of 68 deg and extended to at
least 1.2 deg distance. By Finson-Probstein simulations, the eastward
tail can best be interpretated as being caused by a dust release about 1
hr around perihelion. The maximum beta value in the eastward tail
reaches values up to 1.5, typical for graphite or metallic grains of
about 0.1 micron radius. No indications are found for a continuation of
the release of similar dust after 2 hr post-perihelion. The shorter
southward tail may be a relict of heavier grains released about 1-2 days
before perihelion passage. Diffuse cometary material is noticeable in
the p.a. range covered by the two dust tails. The match of the
synchrone pattern for the eastward tail is not optimal, which may
indicate secondary effects to the dust grains involved.
NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
superseded by text appearing later in the printed IAU Circulars.