Comet ISON's Current Status

Latest Update: November 11th, 2013

The latest light-curve for Comet ISON (compiled November 11, 2013 by Matthew Knight).
Comet C/2012 S1 (ISON) is now inside the orbit of Venus, and has only seventeen days left before it reaches its closest point to the Sun, on November 28, 2013. There's an awful lot that could happen to ISON between now and then, and we really can't say how things will go. All we can do is report on how the comet appeared to be doing the last time we saw it, and thanks to the legions of amateur as professional astronomers around the world, that was just a few hours ago!

It feels like we may have said this once or twice before, but it never hurts to repeat it: Comet ISON is doing just fine! It is maybe a little over a week since we saw the first few reports that ISON was a binocular object for fortunate observers with extremely clear skies. But ISON has brightened up considerably since then, and binocular observations of the comet have become widespread. We've seen a couple of estimates of ISON in the mag 7 - 8 range and so it would not surprise us for there to be one or two naked eye reports later this week, though once again these would only come from a select few lucky observers with amazing views of the night sky. But Comet ISON is moving extremely fast now at around 50km/s (180,000kph, 112,000mph), and will soon become increasingly difficult to observe as it approaches twilight skies. By far the best opportunity for naked-eye viewing of the comet will be in early-to-mid December as it climbs back into the night skies. Of course, this is all dependent on it reaching and surviving perihelion...

Our previous update mentioned the exciting news that we now have X-ray detections of comet ISON from the NASA Chandra X-ray Observatory. We have now expanded on that a little in our Comet ISON Image of the Week feature, and is something we will follow up on in December when we hopefully have more X-ray observations from not only Chandra but maybe the X-ray imagers on the NASA MESSENGER spacecraft.

Also we pointed to a beautiful image taken by astrophotographer Damian Peach, showing very clearly that ISON has developed an ion tail. Since we published that page, several other similarly wonderful images have been recorded such as this one from Michael Jaeger, this from Nick Howes, Ernesto Guido and Martino Nicolini, and this from Gerald Rhemann. Lots more can be seen online, but we encourage everyone to find a local astronomy club and try and see it with your own eyes... and take a child with you!

So the tl;dr today is this: Seventeen days from perihelion, Comet ISON is still in one piece, is brightening nicely, is a binocular object, and currently shows no signs of fading out or fragmenting. We hope that continues for at least eighteen more days...


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.

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