UPDATE: 10:00 UT
It is clear that a part (reduced or fragment) of the nucleus of Comet ISON made it round the sun and is now moving away from the sun. After initally brightening and reforming a dust tail derived from its momentum as it swung around the sun, it seems to be fading now as it moves towards the outer FOV of the Lasco C3 camera of the SOHO observatory. The tail is gradually swinging around to the outbound direction. It will be interesting to see what the mission scientists can gleen from this from the multitude of data sets.
For now my rule of thumb, is really not very sciency, but if a naked eye comet reaches the Lasco C3 FOV - its going round! Not a lot of math in that, but its two from two in 3 years! Seriously though for the real science - read NASA's Comet ISON observing campaign blog which is being regularly updated by respected comet supremo Karl Battams.
UPDATE: 05:30 UT
ISON continues to brighten and a new dust tail appears to be swinging around from its transit path towards its outbound trajectory.
Image Credit: Solar and Heliospheric Observatory - Lasco C3 23:30 UT 28/11/2013
What we know about comets is alot more than we used to know, but not everything there is to know!
Like most people with a passing interest in astronomy I have been following the passage of Comet ISON as it approached perihelion. I have followed the intense debates about what might constitute a "secular light curve" and observed daily predictions and alerts about what was about to happen.
Today it has been hilarious to see people pronounce ISON dead on arrival at perihelion and wander off to their thanksgiving dinner thinking its all over red rover!
Currently twitter is ablaze with witty retorts and updates as some sort of remenant has re-emerged and continues to brighten. Most of the wise observers are doing the appropriate thing and "waiting for more information". So far on twitter it has been re-named Schrodinger's Comet, Schwartzneger's "I'll be back" comet.
Image Credit: Solar and Heliospheric Observatory - Lasco C2
As for me, I am reminded of Comet Lovejoy (2011) which surprised everyone and made it past perihelion and broke up outbound after a spectacular display at Christmas 2011. I couldn't help remembering that the tail didn't really return immediately after perhelion, until the Comet moved away from the immediate vicintiy of the Sun. In fact in 2011 Lovejoy's tail didn't really reform until it was even further out than it is now.
One thing to consider here is that the perspective from which we view these images is only two dimentional, ie whats in the image, and its very hard to tell from that perspective what at the front or behind.
Image credit: Comet Lovejoy (2011) Solar and Heliospheric Observatory - Lasco C3
Whilst comets are not made of sugar, think of creme brulee, the sugar gets heated up, some smoke comes off, it suffers intense heat, changes its composition and comes out the otherside a crunchy piece of toffee with roughly its same mass but slightly different texture. Now this is a bit of a stretch scientifically as I said, as comets are not made of sugar, but with the heat, the increase in speed, the change of direction, the resultant slowing and cooling after perihelion, there is alot going on there that we really just don't know enough about.
Which is why comets are, always have been, and always will be, incredibly undpredicatable.