Quote:
Originally Posted by mithrandir
Aidan, the free programs Stellarium, CdC, and C2A (and probably others I don't have) all support in-program updates of their comet and asteroid databases. Provided the data has both the magnitude data values they will estimate the brightness you can expect.
At the moment it is at 17h26'03" -39°54'54" mag 9.2 visible from a bit after 03:00 AEDT.
Your best chance is probably in the fortnight around Jan 25 when it will be in the morning sky around 02:45 AEDT. CdC predicts Jan 18 mag 8.1, Jan 25 mag 7.4, Feb 1 mag 6.6.
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Unfortunately most (if not all?) planetarium programs update from MPC ephemerides. When a comet is discovered a preliminary ephemeris is prepared with orbital elements and a prediction of brightness behaviour based on a simple formula relating to some fundamental properties of the object and behaviour of similar previous objects. Even as the orbital elements are updated with new astrometry, the m1 predictions are not altered. Therefore if a comet goes into bright outburst or performs better than expected (or worse!), your planetarium program will continue to show the original MPC predictions. Thus we had Starry night, Stellarium etc showing mag 17 or something for comet 17P/Holmes when it was a naked eye object a few years ago, and planetarium programs continuing to give magnitudes for C/2011 W3 (Lovejoy) for months after the comet nucleus effectively ceased to exist.
To get an idea of how a comet is performing, you're better off going to a website with updated light curves. Here, the formula will have been modified to account for a stream of incoming observations. As a one-stop-shop, you can't really beat Seiichi Yoshida's site IMO:
http://www.aerith.net/index.html
http://www.aerith.net/comet/weekly/current.html (click 'South' link at top)
If you go to his C/2011 L4 page you'll see how the comet is going, and is likely to go, in the light curve at the bottom of the page:
http://www.aerith.net/comet/catalog/2011L4/2011L4.html
Currently the light curve doesn't have the latest southern observations since the comet crawled out of daylight but you can expect that they'll be added in the next few days probably. Sometimes more than one formula will fit existing observations and you may see other sites using different formulae. But it is a constant refining process - prediction is not an exact science!
There are many other sources of updated comet information around the web, some good, some bad.
Quote:
Originally Posted by badabing82
So it's confirmed at m 9.1 or their thereabouts currently?
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No, see above. Recent visual obs include m1=9.1 (23 Dec), 8.1 (24 Dec), 8.0 (27 Dec), 8.3 (1 Jan), and Terry's est of around mag 8 on 2 Jan - the comet is not fluctuating in brightness, this is just differences in what people see (exacerbated by low altitude, different instruments & moonlight). So the trend is that it
appears to be a bit visually brighter than the ephemeris magnitude, so brighter than mag 9.1. And brightening all the time.
Cheers -