Comet ISON's Current Status

Latest Update: November 23th, 2013



The latest light-curve for Comet ISON (compiled November 22, 2013 by Matthew Knight).
It has been a couple of days since our last update on here, for which we apologize. The past few days have been one of transition for the CIOC Team as we gear ourselves up for this coming week.

There isn't a huge amount that's new with the comet, though. (If there were, we absolutely would have reported it here!) At time of writing, comet ISON is 0.3AU from the Sun (28,000,000miles, 45,000,000km) and traveling at a rather impressive 77km/s (172,000mph, 277,000kph). It is still visible in the pre-dawn skies but with increasing amounts of effort as it is really starting to hurtle towards the Sun now. Ground observers may still have a day or two left to see it but we don't think much more than that as the skies just get too bright too quickly.

Visual magnitudes are now accordingly hard to estimate, as sunlight pollutes the field of view. We're seeing reports of values in the magnitude +3 to +4 range, which sounds about right. We have updated out lightcurve (opposite) with the most recent data available, but again that's pretty spotty.

Rumors to persist about whether the nucleus has fragmented, but we still see no direct evidence. There are a number of interesting coma structures and "knots" in the comet's tail, but are most likely just the result of solar wind influence.

Talking of which, hopefully you've seen that ISON is now visible in the HI-1 camera on NASA's STEREO-A satellite. We are seeing some beautiful tail dynamics in there, and we have the bonus of comet Encke in the field of view. Read Karl's blog post about why that's particularly exciting. Fellow CIOC-er Matthew has started photometric analysis of that data and his preliminary results are more or less in-line with what ground observers are reporting.

We will have more information on this and the other solar spacecraft observations in the coming days. We're into the final few days before perihelion and the ESA and NASA fleet of sun-watching spacecraft will be our only eyes during this time. Fortunately both Matthew and Karl have worked with this data for over ten years, and so they'll both be on hand to guide you through the events of the week. We can't promise what ISON will do, but we can promise it's about to get intense and exciting! Don't stray far from this website in the coming days!

For now, the tl;dr is that ISON continues to head towards the Sun, it appears to still be in one piece, and is basically brightening up exactly how we'd expect. Ground based observations are almost impossible, and we've now entered the realm of solar spacecraft observing. The next few days are where the fun really begins...

Light-Curve

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.

First, 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 comet, 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, 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 overlap. 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, and will therefore be harder to detect the full coma or to compare it to nearby stars. At some point we will likely stopping 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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