Comet C/2011 L4 (PANSTARRS)
Posted 01 February 2013 - 12:39 PM
Posted 01 February 2013 - 01:19 PM
It's now Feb. the Moon is slowly going away I'm waiting for another obs.
Comet C/2011 L4 (PANSTARRS) will reach its maximum southerly declination of 45.6° on 2013 FEB 05 where it is essentially out of sight for observers well north of the tropics. However it will soon be headed northward as the charts and ephemeris on my comets webpage indicate: www.CurtRenz.com/comets
During late February the comet will appear to pass the first magnitude star Fomalhaut. The separation will be only 2.5° on February 26. Unfortunately the Sun will also appear in the vicinity. Below is an equatorial chart I created to illustrate the close approach.
Posted 02 February 2013 - 05:58 AM
Posted 02 February 2013 - 08:46 AM
Once again re-evaluating the growing body of photometric data ths morning and using 26 selected observations spanning Jan. 01 to Feb 02 results in the formula:
m1 = 5.6 + 5 log(D) + 6.6 log r
implying a maximum brightness of no more than +2.0
Posted 02 February 2013 - 01:05 PM
Posted 04 February 2013 - 09:13 PM
Its been a while since a mag +2 comet anyway so I wont sniff at that.
I would not laugh at a magnitude 2 comet either as they are rare as well. Comets are hard to predict.
Posted 06 February 2013 - 11:33 AM
Hey, the comet is now making nice gas tail. What does it mean for us?
Probably nothing very heartening, I'm afraid. Were PanSTARRS a more active comet one would have anticipated the development of an ion tail significantly early than this. In fact, there apparently still wasn't a detectable one even as late as last week! By way of comparison look at the ion tail on Comet Lemmon which is more typical of a type I tail (and has been present for some time) while currently at 1.2 a.u. from the Sun. Then compared that with PanSTARRS', with that comet at 0.91 a.u. Pretty darn weak, I'd say.
Likewise, the latest observations would seem to indicate that the comet's brightness may be beginning to fall behind even that predicted by the magnitude formula I had posted up-stream, making the prediction of a peak brightness of +2.0 in mid March ever less likely.
Posted 06 February 2013 - 10:44 PM
What magnitude was hale-Bopp or hyakutake?
At their peaks, -0.5 and 0.0 respectively.
Posted 06 February 2013 - 10:48 PM
Still 2+ is impressive in my book. Very-good is entirely acceptable . Frankly anything brighter mag 6 to me is good so this ought to be refreshing.
Posted 07 February 2013 - 02:17 AM
What magnitude was hale-Bopp or hyakutake?
What significance does it have? They were visible on dark sky easily with naked eye. There is no chance to see +2 mag object with naked eye so low over the horizon + on so bright sky. To me it's no comparison!
Posted 08 February 2013 - 06:45 AM
There is no chance to see +2 mag object with naked eye so low over the horizon + on so bright sky. To me it's no comparison!
Its called a washout!
Posted 09 February 2013 - 09:48 AM
m1 = 5.6 + 5 log(D) + 6.7 log® , cc = 0.93
The fit to the data is excellent and it is noted that these parameters are hardly any different from those derived a week ago, suggesting that these terms are becoming quite certain now. They are also rather similar to those derived for Comet Kohoutek back in 1974. Descriptions using binoculars and small telescopes continue to indicate a bright pseudo nucleus within the coma and a short but obvious and rather dramatically curved dust tail, with the ion tail almost absent.
Considering our viewing geometry in mid to late March the above implies an ever more probable peak magnitude of close to +2.5 with the comet displaying a broad, highly curved tail, perhaps of rather low surface brightness which will have reduced visibility particularly when viewed at low elevation against a twilight backdrop.
Posted 09 February 2013 - 11:08 AM
Mr. Bortle, what do you think about comet Kohoutek's return to a higher n at log® < -0.6? Would it be reasonable to expect something similar from PanSTARRS?
Posted 10 February 2013 - 08:28 AM
I would also note that, in my opinion, total magnitude determinations when a comet is further than 2.5 a.u. from the Sun should be regarded as increasingly suspect, particularly those made during the post-T interval, for a number of quite valid reasons.
Posted 11 February 2013 - 03:32 PM
There are tables provided for altitude to every 0.5 km to account for Rayleigh scattering and the 0.016-mag/air mass extinction for ozone is essentially "baked into the cake".
It's the aerosol extinction, though, that perhaps needs a makeover. There are three tables to account for various aerosol loads ("average", "winter", and "summer"), with the "average" set at 0.120-mag/air-mass and the winter and summer values set at 70% and 130% of that, respectively.
There are multiple issues I've got with this approach. (1) The "winter" extinction table can be used year-round at desert locations and most of Australia, and even that doesn't account for how clean the air can be in these locations. Likewise (2) some locations with humidity and high industrial emissions rarely have clean enough air to justify the "average" extinction table, and (3) the aerosol extinction is assumed to decrease logarithmically with altitude. Normally that's the case, but there could high-altitude haze (e.g. forest fire smoke, volcanic ash) that might be absent from the lowest 10,000-ft altogether.
Aerosol extinction, in other words, simply is what it is for a particular location and time. The only way to really account for it in your estimate is to compare the brightness of stars low along the horizon with those near overhead and to back-calculate the aerosol (and, thus, total) extinction if--IF--an estimate needs to be corrected for atmospheric extinction. It'd be very cumbersome to put it in tabular form, but a simple spreadsheet program with a few inputs would easily suffice.
Obviously an experienced comet observer should go out of his/her way to seek out suitable comparison stars at similar altitudes as the comet to avoid the use of extinction tables altogether, but some comets take away that option from the get-go. And I'd concede that the methodology of the observer can easily introduce as much error and uncertainty as atmospheric extinction to begin with. It's just something that's bothered me for some time, and the low elevation of C/2011 L4 at its brightest just reminds me of it. This isn't meant to be a slight to Dr. Green's very important and well-researched 1992 ICQ article regarding atmospheric extinction; quite the opposite. Maybe it's time to update to procedure a bit by tailoring the equations to specific conditions and locations.
Posted 16 February 2013 - 09:29 AM
m1 = 5.6 + 5 log(D) + 7.1 log® cc = 0.97
If carried to perihelion this implies a peak magnitude of 2.1 as seen from the Earth during mid March.
Reports of the comet's appearance as seen with with small instruments and binoculars this week indicates the head to be extremely condensed and the typical double tails (ion and dust) are now both apparent and photographically of almost equal length.
Posted 16 February 2013 - 08:55 PM
Posted 17 February 2013 - 11:33 AM
Comet will be in twilght skies. Would like to see it in darker skies, but appreciate any view I can get of this comet in the March skies. Expecting clouds on the horizon to be a hinderence.
Posted 17 February 2013 - 05:10 PM
The head of Comet PanSTARRS will be seen only very low and in the western twilight well into April for mid northern latitude observers, by which time C/2011 L4 will have faded considerably. At the same time odds are that the comet's bluish ion tail could prove difficult to recognize, particularly visually, in the intense twilight. The brighter and more visually apparent dust tail is likely to initially be directed toward the southeast at a low angle and largely subdued by the bright sky. The latter appendage may likely not be seen to project more-or-less upwards in classic comet fashion until fairly late in March, by which time the moon, then in its gibbous phase, could severely hamper any visibility.
So, astro photographers are likely to be faced with a catch as catch can senario, attempting to trade off comet altitude, favorable tail direction, twilight and moonlight interference to gain any impressive images.