SPA Comet News, October 2003

It has been rather longer than I intended since I wrote an update on whatís on in the cometary world.Since my last piece I have visited Antarctica again, and also Mallorca for an amateur meeting on asteroids and comets.The comets that I wrote about last time have come and gone, but they did put on a splendid show.Comet NEAT (2002 V1) was well observed before it headed south and was a beautiful sight in the mid February evening twilight.I was able to recover it from Rothera station on the Antarctic Peninsula, but weather conditions in the Antarctic autumn were very cloudy and I had few chances to see the night sky.

Whilst there I was also able to observe comet Kudo-Fujikawa (2002 X5), however by the time it had returned to northern skies it had all but faded beyond visibility in small telescopes.Comet Juels-Holvorcem (2002 Y1) did pretty well, reaching 6th magnitude in late March and early April, but was too far south for observation after mid April.Several people contributed observations, including Stephen Getliffe and Mike Feist.There havenít been any comets to observe over the summer, so you havenít missed anything.One exciting bit of news that did come out was an observation of comet 1P/Halley at the incredible distance of 28 AU.

Coming up this autumn are a couple of comets that should become visible in binoculars: 2P/Encke and 2002 T7 (LINEAR).We have seen more returns of comet 2P/Encke than any other comet.First observed in 1786 by Pierre Mechain, it was next seen by Caroline Herschel in 1795, with further recoveries in 1805 (Pons, Huth and Bouvard) and 1818 (Pons).Johann Encke was now finally able to link the four objects and it then became Enckeís comet.This yearís return is almost a re-run of 1795, with perihelion only 8 days later, on December 29.9.Two hundred yearís ago it was discovered on November 7.8, when it was around magnitude 5.5 and visible to the naked eye according to William Herschel.Observers followed it until the end of the month. What will happen this time round?Although BAA observations show no significant change to the cometís absolute magnitude in the last 50 years, there is some evidence that its pattern of activity has changed over the 200 years and it is now brighter post perihelion than pre perihelion.By early November it is likely to be around 10th magnitude and may brighten to 6th magnitude by the time we loose it in early December.Although probably not obvious to visual observers, the comet often develops a thin ion tail and this may show in CCD images.

2002 T7 (LINEAR) is still some way from perihelion, which is at 0.61 AU on April 23.1 next year.By early November it will still be 2.9 AU from the Sun, but is likely to be 10th magnitude.It will probably be easier to see than most 10th magnitude comets, as it is well condensed, thus making it much easier to pick out in our light polluted skies.It brightens only slowly, but will possibly reach naked eye brightness by the time it gets too far south for us to observe in mid March 2004.It is still over an AU from the Sun at that time, so significant tail development is unlikely.We must then wait patiently until early May when comet 2001 Q4 (NEAT) arrows up from the southern hemisphere into our skies, possibly as an impressive naked eye object.

Comets can spring surprises at any time and it is always worth keeping an eye out for comets, even when they are predicted to be fainter than normally visible with your instrumentation.The most recent example of such a surprise was the rediscovery of a comet last seen in 1978 at its only observed apparition.Seen over the relatively short arc of a month, comet P/Tritton hadnít been seen at subsequent returns and was presumed lost, although it was predicted to return in March this year.Then Charles Juels and Paulo Holvorcem discovered a fast moving cometary object on CCD images taken in early October and this was linked to the lost comet.It turns out that the period was a little longer than expected, but the comet was also clearly much brighter than expected on the basis of the first apparition.Such outbursts can happen in any comet, so there is always a chance that even the usually reliable comet Encke will spring a surprise.

The winner of the competition for the Springer book on 'Observing Comets' by Nick James and Gerald North was Margaret Cullen for her drawing entitled ďWatching Hale-BoppĒ.Runners up were Malcolm Gibb with a photograph of Ikeya-Zhang above the mountains near Callendar and Sidney Hurring with a white on black sketch of the rotational shells seen in the coma of Hale-Bopp.

For more information on current comets and the latest updates on comets 2P/Encke, 2001 Q4 (NEAT) and 2002 T7 (LINEAR) see my web page at http://www.ast.cam.ac.uk/~jdsUpdates on the progress of all the comets will be posted in the SPA ENBs.Iím heading off to Antarctica again in mid February, but will be back by the end of March.We are getting a new satellite data link installed whilst Iím there and there is a chance that Iíll be able to update the web page during my absence.

Jonathan Shanklin