Comet ISON's Current Status

Latest Update: December 5th, 2013

The latest light-curve for Comet ISON (compiled December 5, 2013 by Matthew Knight).
It is now about a week after perihelion and things have been slow since our last report. Why have we been so quiet? Because we haven't had any substantial new information to report (and because we're all recovering the whirlwind of last week!).

Comet ISON left the LASCO C3 field of view early on December 1 as a diffuse object lacking a central condensation down to the instrument's limiting magnitude of about +8.5. It appeared in STEREO-HI1A around this same time and is expected to remain in the field of view through about December 7. As of December 3, 2013 (the most recent images available as of this writing), a broad and diffuse remnant of comet ISON continues to be visible in STEREO HI-1A images. Due to a complete lack of any kind of central condensation down to the instrument's limiting magnitude of about +13.5, photometry is impossible at this stage. A by-eye estimate would be that the comet remnants continue to drop at approximately half a magnitude per day, and in the most recent images appear to be around magnitude +11. We will update the lightcurve if/when there are new measurements reported.

We continue to encourage observations of comet ISON to help understand what, if anything remains. It is our hope that subsequent observations when it is at a more favorable solar elongation and closer to the Earth may be able to detect or set upper limits on any remaining nucleus/fragments or gas production. Such measurements will be vital for understanding what was the ultimate fate of ISON. At this stage our working assumption is that it disintegrated, but it is plausible that the nucleus was simply devolatilized, or that there exists one or more small fragments each of which is active at a level too low to be detected by SOHO or STEREO.


Some notes about the lightcurve plot:

We plot 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. The ICQ data are generally “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 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 near perihelion the ICQ data fall much closer to the trend line, but back in the first half of 2013, the red and blue points roughly overlap. This is because in early 2013 Comet ISON had a small angular size, so in effect all brightness measurements were “total” measurements. Once ISON got close to the Sun, its coma was much larger in an absolute sense. Furthermore, it was also closer to the Earth, so its apparent size was also larger. The result is that what worked very well early on (measurements using a small aperture on a CCD) began to diverge systematically from the total brightness. So near perihelion the blue points do a better job answering what everyone cares about: “How bright is Comet ISON?

The black line is just one possible model of ISON's brightness behavior. It makes no prediction for what comet ISON will actually do. After being steadily adjusted throughout the first ten months of 2013, the line ended up doing a fairly good job of matching most of the "total brightness" measurements leading up to perihelion. Due to comet ISON"s apparent demise near perihelion, the post-perihelion curve is obviously no longer very relevant. However, any small active fragment that might still exist would likely follow this rough shape, albeit with a MUCH lower brightness.

The gray box is a zoomed in plot of the most recent data. If new brightness measurements are obtained this will continue to show the new measurements in greater detail.

The "Current Status" page will not be updated further unless there are new measurements reported. You are encouraged to follow the CIOC's Karl Battams '@SungrazerComets' Twitter feed to learn more about comet ISON and other sungrazing comets.

Current Status Archive

As this has been a dynamic page throughout the website's existence, it was unwieldy to display previous status updates. You can go directly to previous updates below, but note that near perihelion more information was conveyed through the blogs.
November 30
November 27
November 25
November 23
November 20
November 19
November 18
November 15
November 13
November 11
November 8
November 6
November 2

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