[X] My Assistant

[Greenish]

A GIF (click to animate) of the last day and a half, from the STEREO Behind COR imager. Can see the CME.



(I know the spacecraft websites can make movies, but they seem pretty heavily loaded right now, and I wanted to see how it would come out.)

[scalbers]

From my original light curve peaking at -6, ISON should be about magnitude 0.5 right now at 1800UTC. The LASCO C3 image has it blooming and brighter than the object in the left side. I believe that is Antares as even the globular cluster M4 is visible nearby. Thus ISON might be about the "right" magnitude.

http://sohowww.nascom.nasa.gov/data/realti...1024/latest.jpg



Here are my ephemerides:

http://laps.noaa.gov/albers/ast/eph/ISON.2012S1.co.html

http://laps.noaa.gov/albers/ast/eph/ISON_h....2012S1.co.html

[Mongo]

From my original light curve peaking at -6, ISON should be about magnitude 0.5 right now at 1800UTC. The LASCO C3 image has it blooming and brighter than the object in the left side. Is that Antares? Thus it might be about the "right" magnitude.

That bright star is indeed Antares. The light bloom from ISON is definitely longer than the one from Antares, so everything else being equal, your original light curve looks correct.

Of course Antares is quite red, and I don't know the spectral response of the detectors used in LASCO C3, so it could be off by some amount. But I would think that the detectors would be close to equally efficient at all visible light frequencies.

edit -- from the latest CIOC blog entry, When Will We Know?:

In the above LASCO image, you'll see that I have pointed to a saturation spike in the comet's nucleus. This mean that it is becoming too bright for the current exposure time on those images (we'll fix that, don't worry) and the pixels on the camera are "bleeding". We've seen a lot of bright comets, planets and stars in this camera and by experience alone we know that this corresponds to a visual magnitude of around +0.5.

edit -- from the even more recent Comet ISON's Current Status entry:

Now that we have observations of the comet in the NASA STEREO instruments and, more recently, the ESA/NASA SOHO LASCO C3 instrument, CIOC team member Matthew Knight has been able to start recording photometry of the comet. His results seem to imply that the comet may have experienced an outburst during the (approximate) period Nov 21 - 23 with corresponding brightness increase, followed by a leveling off and then dropping back down to "pre-outburst" levels. Since entering the LASCO C3 field of view, comet ISON has increased by at least a factor of four, and indications are it may be closer to a factor of ten. In the most recently available images, the comet appears to be around magnitude +0.5.

It is now the opinion of the CIOC Team that Comet ISON is now behaving like a sungrazing comet. We can not comment on whether the nucleus is in tact or not, but our analyses indicate that its rate of brightening is directly in line with that we have experienced with other sungrazing comets. This has no implication on its chances of survival. We strongly encourage all professional solar observatories who have plans in place for observing the comet, to please do so, and the teams should plan for an object brighter than negative one magnitude (and we are being conservative on this estimate).

[Phil Stooke]

Greenish - fantabulous!

Phil

[Mongo]

According to this distance calculator, ISON is now crossing the 0.1 AU line inbound.

Comet ISON's bloom line has lengthened substantially in the most recent C3 image, which updated just a few minutes ago. It is now significantly longer than the one for Antares.

[scalbers]

Just for reference I found this YouTube video of Comet McNaught in 2007. This gives an idea of what a -5.5 or so magnitude comet would look like.

http://www.youtube.com/watch?v=EAJgVK-WnHY

The pace of the "nominal" light curve should increase ISON to 0.0 magnitude by 0000UTC on Nov 28th (5 hours from now).

Steve

[Greenish]

Thanks, Phil. Didn't do much -- learning a lot as usual.

For those who want to play with the (vast) trove of data the STEREO pair produce nonstop, an easy starting point appears to be: http://stereo.gsfc.nasa.gov/browse/2013/11/27/ (you can enter other dates in the link or at the top of that page).

Then if you scroll down to the sensor of interest (in this case COR2), there are links to various resolutions underneath, and you can get to either lists of images (i.e. http://stereo.gsfc.nasa.gov/browse/2013/11...hind/cor2/1024) or movies. These are all low-res browse images; the hi-res images take some time. There are also FITS versions elsewhere on the site.

Oh: and the bright spot above the comet is Jupiter in my GIF above.

[Mongo]

It appears that ISON has become much brighter in the past few minutes. This link currently shows the 20:30 image from LASCO C3, and ISON has hugely increased in brightness! From Twitter:

Sungrazer Comets @SungrazerComets 4m

WOAH... #ISON has seriously flared up...

Sungrazer Comets @SungrazerComets 1m

I've just requested they drop the exposure times for the LASCO images because the saturation at #ISON's head is just too strong now.

mars_stu @mars_stu 4m

@SungrazerComets negative mag yet?

Sungrazer Comets @SungrazerComets 39s

@mars_stu Oh yeah! Conservatively #ISON is mag -0.5 right now but I suspect it's close to -1 or so...

[scalbers]

Robert Matson estimates -1.0 to -1.5 in this message.

-----------------------------------------------------------------------------------------------------------------------------------

http://groups.yahoo.com/neo/groups/comets-...ns/topics/22552

ISON is definitely into negative magnitudes as seen in LASCO C3
in the 27 November 20:42 image -- I estimate somewhere between
-1 and -1.5 based on the degree of saturation for the clear filter
at 17.6-second integration time. Compare to the lengths of the
saturation spikes of Mercury and Jupiter:

http://sungrazer.nrl.navy.mil/index.php?p=transits/transits

keeping in mind that today's exposure duration is a little bit
shorter than the typical 19.1-second exposures that were used
years ago. In the 2000 image at the above link, Jupiter was
at around mag -1.6. --Rob

---------------------------------------------------------------------------------------------------------------------------------

I've now bumped up my predicted light curve by 1.2 magnitudes brighter. Hopefully I won't be vacillating too much on this like I have been to some extent.

Steve

[Mongo]

ISON continues to brighten at a ferocious rate. The most recently released LASCO C3 image at this time (21:32) shows significantly longer bleed lines than the image labeled 20:42. I would say about 20-25% longer. I don't know what magnitude the current bleed line lengths would imply -- perhaps magnitude -2?

I think that it's safe to say that ISON has "switched on" again.

[scalbers]

It seems the length of the spike is about 2/3 the amount of Jupiter at -1.6 magnitude in the sample image linked two posts above. If we account for the slightly shorter exposure time now, perhaps it's about like -1.4 or so?

[Mongo]

It seems the length of the spike is about 2/3 the amount of Jupiter at -1.6 magnitude in the sample image linked two posts above. If we account for the slightly shorter exposure time now, perhaps it's about like -1.4 or so?

The standard exposure time has dropped from 19.1s in the 2000 images, to 17.6s now, for about an 8% drop in exposure time. How this affects the length of the bleed lines, I don't know. I suppose I'll simply wait for an update on ISON's current brightness from Matthew Knight or another member of the CIOC team.

[Mongo]

ISON's rapid brightening continues. The new 22:30 image from C3 shows bleed lines that have extended another 20% or so from the 21:32 image.

edit -- the newest ISON image at 23:06 shows another ~5% increase in bleed line length.

[scalbers]

Nice image again at 23:30UTC from LASCO C3. I'll go out on a limb and estimate -1.5 magnitude from the bleed lines.

[Mongo]

Another 15% increase in bleed line length with the 00:30 image. Comparing the 20:42 image (20 minutes after Robert Matson estimated that ISON was in the -1.0 to -1.5 magnitude range) and 00:30 image, we see a 95% increase in bleed line length in less than 4 hours. What could its brightness be now?

edit -- Not an exact answer, but an indication of one:

Sungrazer Comets @SungrazerComets 12m

Latest from #CIOC's Matthew: #ISON's brightness has increased another factor of two over the past couple of hours!

Sungrazer Comets @SungrazerComets 9m

Ladies and Gentleman, I am delighted to say that we have a very, VERY bright comet on our hands. #ISON is certainly not disappointing us!