Comet ISON's Current Status

Latest Update: November 15th, 2013

The latest light-curve for Comet ISON (compiled November 15, 2013 by Matthew Knight).
The past 48-hours have been rather exciting, to say the least. Two days ago we reported that "something different" appeared to be happening with comet ISON, and that we were seeing several anecdotal reports that maybe the comet was experiencing an outburst. Well those reports were not wrong, and comet C/2012 S1 (ISON) has suddenly become a truly beautiful comet!

Comet ISON's brightness appears to be around two orders of magnitude brighter now, with reports of visual magnitude in the region of +5 to +6. For those with very dark skies, this now makes it a naked eye object, and even for those in urban environments it is readily visible as a fuzzy green blob about half an hour before sunrise in the south eastern skies.

However, while it is great news that ISON is now so bright, the future of the comet is still very uncertain. We lay this out in detail in our latest blog post, so we urge you to go and read that to better understand what all this fuss does, or doesn't, mean for ISON. If you want to see ISON with your own eyes, do it now. We can not and do not guarantee that it will survive the next few weeks and become naked-eye visible in our night skies. Also, if you have the capability, we are urging everyone to make spectroscopic measurements of the comet as all this new, primitive material is being exposed to the solar wind. (If ISON dies, let it die in the name of science!)

Finally we want to draw your attention to the new design of our popular lightcurve, opposite. There are some important differences to make note of, and we explain them in the bottom-half of this page (which will remain more or less static in future updates to this page).

So today's tl;dr is this: Thirteen days from perihelion, comet ISON has become very bright and beautiful, but its fate is very much in the balance. You have maybe a handful more days to get out and see it in binoculars before it is lost in the Sun's glare... perhaps forever! (Don't point binoculars at or near the Sun - ever!)


Frequent visitors to this page will notice that the above lightcurve plot has been overhauled. It is now a bit busier, but is also conveying more information and is hopefully easier to see exactly what’s going on right now. In a nutshell, here is what is new.

We are now plotting two sources of data. The first, shown as red circles, are the magnitude measurements being reported by the Minor Planet Center. As we’ve discussed before, these measurements vary widely from observer to observer based on each person’s technique and instrumentation. Most are only measuring a relatively small region near the nucleus, yielding a fainter brightness than if they measured the whole coma.

The second, plotted as blue triangles, are from the International Comet Quarterly (thanks to Alexandre Amorim for pointing this out to us). These data had not previously been plotted here, but are quite useful. The ICQ data are “total magnitude” estimates that try to encompass all of the light from the comet. Many of these estimates are made by very experienced observers using binoculars or even (soon) their naked eye who compare the comet to nearby stars of known brightness. It takes a lot of work to be good at this technique, but as you can see from the relatively small scatter in the blue points, it yields quite reliable estimates.

You will notice that the ICQ data fall much closer to the trend line we’ve been plotting all along, but back in the first half of 2013, the red and blue points roughly overlapped. This is because back then Comet ISON had a small angular size, so in effect all brightness measurements were “total” measurements. Now that ISON is much closer to the Sun, its coma is much larger in an absolute sense. Furthermore, it is also closer to the Earth, so its apparent size is also larger. The result is that what worked very well early on (measurements using a small aperture on a CCD) has begun to diverge systematically from the total brightness. So now the blue points do a better job answering what everyone cares about: “How bright is Comet ISON?

The other big change we’ve made is to create a smaller, zoomed in plot that only shows the most recent data. This gives a much better idea of how closely the current estimates are following the trend line. The immediate takeaway is that the huge brightness increase over the last few days isn’t that surprising, and we can probably hope to see similar brightness gains on a daily basis over the next two weeks (assuming ISON hasn’t broken up)!

It will, of course, become harder for people to estimate the brightness as ISON gets closer to the Sun because the sky will get brighter when ISON is observed. This makes it harder to detect the full coma or to compare it to nearby stars. At some point we will likely stop getting new ground-based brightness estimates and will have to start relying on observations from the SOHO and STEREO spacecraft. But rest assured, we will plot data here as frequently as we can, so please keep checking back.

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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