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Night Sky NewsStalking Comet PANSTARRS C2011/L4 - Spring 2013

Stalking Comet PANSTARRS C2011/L4 – Spring 2013

Comet PANSTARRS C20011/L4  hide-and-go-seek …

If you have tried to find a bright comet gracing our spring skies this year, you may have been thwarted;  you may find that the altitude of the comet is so low that it hides behind a clump of trees. Although we must suffer the ‘cloud of witnesses’ ( I have seen annoying cloud banks congregate at sunset to conceal the comet), we do know that Comet PANSTARRS C2011/L will  gain altitude as it sails away from the sun.

The ‘Naming’ of Comets…

Learn the  ‘cometary’ nomenclature. That will help you find and track a particular comet of interest. First thing to note, there may be more than one comet with the same ‘name’. We need to qualify the name to determine the one currently above our local horizon at the time of interest. For example, there’s more than one comet PANSTARRS. That’s because it was discovered by The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS)  which hosts an array of astronomical cameras , telescopes and  a significant computing facility . The current comet of interest was discovered in 2011 in the 1/2 month L which would be the first half of June (‘I’ is unused), according to the resolution passed by  the International Astronomical Union,  On the Cometary Designation System:

  1. …it is resolved … that  each cometary discovery is given a designation consisting of the year of observation, the upper-case code letter identifying the halfmonth of observation during that year according to the procedure used for minor planets, and a consecutive numeral to indicate the order of discovery announcement during that halfmonth. Each new designation shall be supplied by the IAU Central Bureau for Astronomical Telegrams when the discovery is announced in one of its Circulars. For example, the third comet reported as discovered during the second half of February 1995 would be designated 1995 D3.
  2. The nature of an object can further be indicated by an initial prefix. In particular, such prefixes should be applied in cases where comets have possibly been misdesignated as minor planets, or vice versa. If necessary, the prefix A/ would precede a comet designation that actually refers to a minor planet (or asteroid). For comets the acceptable prefixes are P/ for a periodic comet (defined to have a revolution period of less than 200 years or confirmed observations at more than one perihelion passage) and C/ for a comet that is not periodic (in this sense), with the addition of X/ for a comet for which a meaningful orbit can not be computed and D/ for a periodic comet that no longer exists or is deemed to have disappeared.

 So that’s how Comet PANSTARRS C2011/L4 got its name. It is not considered to be periodic (the ephemerides tell us that); hence *{C} discovered {2011} in the firsthalf/month of June, being the {4}th comet discovery reported in that month

Comet Orbital Elements (Ephemerides)

In order to determine whether it is periodic or not, we can check the ephemerides (those parameters that uniquely determine a comets orbit in space):

For comet PANSTARRSC2011/L4 we have (for the next little while):

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   m1    m2

2013 03 29    00 32 37.5 +32 31 12   1.2507  0.6180    29.2    52.1   3.9
2013 03 30    00 32 11.0 +33 54 04   1.2589  0.6401    30.2    51.8   4.1
2013 03 31    00 31 44.1 +35 14 43   1.2672  0.6622    31.2    51.4   4.2
2013 04 01    00 31 16.9 +36 33 19   1.2755  0.6842    32.2    51.1   4.4
2013 04 02    00 30 49.6 +37 50 00   1.2838  0.7062    33.2    50.7   4.5
2013 04 03    00 30 22.2 +39 04 54   1.2921  0.7281    34.1    50.4   4.7

Stalking the Comet

These elements can be transferred into a computer program like Earth Centered Universe (by Canadian Astronomer Dave Lane). Once the elements are loaded, the program can plot the trajectory of the comet for a given date. We use a coordinate transformation (well ECU does) to convert the Right Ascension and Declination of the object into our altitude and azimuth on the horizon.  ECU shows you  azimuth and altitude  for your viewing location and time of day. Here’s an animation of the comet against the celestial background.  Notice that the sun is below the horizon, the comet is above the horizon and climbing as we leave March and go into April skies. Click once on the image to view the animation.

  … Unfortunately it will also become more difficult to spot as the value of the apparent magnitude increases. (Larger numbers indicate fainter objects: according to the law (-2.5 x log(I) where I is a measure of Light Intensity)  As mentioned earlier, you need a clear slightly north of west horizon. By clear, we mean cloud-free and clear of trees and structures on the horizon. Since the comet is currently only 13 degrees above the horizon, you need to get away from the trees! My current observing location has made it impossible for me to capture the comet from my site. Looking through the scope it’s tangled in trees and often low clouds of sunset. If you take the time to stalk the comet, post your observations.  You will want at least binoculars on  your field trip.

Comets – (5) Discovered in Mississippi Mills

Thanks to the continued preservation of the night sky around the Mill of Kintail, the local dark skies have permitted the visual discovery of  5 comets, marking our Fred Lossing Observatory (FLO)  the only observatory with this distinction. This suggests, you don’t need a PANSTARRS automated observatory to actually discover a comet, never before seen.
Once you have confirmed your discovery, and subsequent observations are made, it enters the list of IAU Comets. A telescope, a passion for stalking,  and a good knowledge of comets and where to look is the first step. For more Canadian Comet Lore, see  
(noting that those 5 discoveries were made at our FLO site within the Mill of Kintail).





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