Comet ISON's Current Status

Latest Update: November 2nd, 2013

The latest light-curve for Comet ISON (compiled November 04, 2013 by Matthew Knight).
Comet ISON remains in one piece, and is now inside Earth's orbit at 0.90AU at time of writing. Over the past few weeks it has brightened up more or less as we expected it to, and just a few days ago we saw the first reports of ground-based observers being able to view ISON through binoculars. It is important to note, however, that these were under ideal viewing conditions i.e. on the top of a mountain! For most viewers in the Northern Hemisphere, ISON is visible in small to medium telescopes with a brightness around magnitude +8 or +9. There are numerous beautiful images of ISON appearing online now from all over the world from professional and amateur observers.

We are less than four weeks from perihelion now, so we would expect ISON to really start picking up in brightness very quickly at this stage. We are not seeing such reports right now, so that is of slight concern. It's not fading out, but ideally we'd like to see it climbing a little faster than it is. That said, it's a sungrazer, and in the week leading up to perihelion it should brighten up by many orders of magnitude if it is anything like the couple of thousand sungrazers observed by SOHO and STEREO over the past 16yrs. But that will require it to actually reach perihelion... and that's something we can't promise (nor have we ever done). A couple of well-reasoned studies (not yet published but hopefully soon) are indicating that ISON's nucleus is a little smaller than first thought (which wasn't big in the first place). This could have implications for its survivability at perihelion.

So this perhaps sounds a little "doom-and-gloom", but don't despair. We do still lean towards the opinion that it will reach perihelion, and if it does so then at the very least it should be a spectacular sight in the solar space telescopes. Absolutely no promises about ground observing post-perihelion, though - sorry!

Above is the latest "light-curve" we have for comet ISON, based upon data submitted by astronomers to the Minor Planet Center. This plot was created by the CIOC's Matthew Knight. There are a couple of important features to note:

1. You will notice that the peak of this plot is not shown. Why? Because it's meaningless. It is extremely difficult to accurately predict the peak brightness of almost any comet, but this is particularly the case the closer a comet approaches to the Sun. ISON is a Sungrazing comet, following an orbit that will take it through the Sun's extended outer atmosphere ("corona"). During this period it will experience intense bombardment of solar radiation and its surface will sublimate (turn directly from solid to gas) at an almost alarming rate. In addition, it will experience extreme structural stresses from the Sun's enormous gravitational pull. These factors lead sungrazers in particular to behave very unpredictably, and we can only guess at how bright it will be, or even if it will survive. That said, we on the CIOC Team have for many months now held to our opinion that ISON's peak brightness (which will occur in the few hours surrounding perihelion) could be anywhere from magnitude -7 to +5 or more, though our educated guesses are hovering around -3 to -5.

2. The black line in this plot is a simplified model of the predicted trend of ISON's brightness. It is not a line that is fitted to the data, nor is it a line to which the data should aspire. You can almost consider this as two different plots that share an axis: a possible model of ISON's brightness (in this case, we use JPL's model parameters), and the reported observations from ground observers.

3. The large spread in magnitudes reported by observers is not a surprise. Viewing conditions differ for all observers, as does the skill level of the observer, the quality and type of instrumentation they use, the kinds of filters they use, and their method for estimating the brightness. It is very common to see such a divergence in reported values (comet Hale-Bopp is a great example.)

If you browse around online you will easily find references to estimates of magnitude -10 or even -15, and the term "Comet of the Century" has been tossed around with abandon. Those are not the words or the opinion of the CIOC Team, and while they may perhaps turn out to be true, we think it extremely unlikely. Likewise, reports of its imminent demise are completely unfounded, and while they may prove to be true, they are currently based on speculation and selective interpretation of data. More likely, ISON should turn out to be one of the brighter comets in the past several years and, thanks to the global astronomy community, we hope one of the most broadly observed comets in history!

Now we're around perihelion time for ISON, we will update this "Current Status" page more frequently -- in some cases daily. Check back regularly for updates, and follow the CIOC's Karl Battams '@SungrazerComets' Twitter feed for more CIOC, ISON and comet news.

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