It has been rather longer than I intended since I
wrote an update on what’s 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 haven’t been any
comets to observe over the summer, so you haven’t 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 Encke’s comet. This year’s return is almost a re-run of 1795, with perihelion
only 8 days later, on December 29.9.
Two hundred year’s 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 comet’s 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 hadn’t 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 “Watching Hale-Bopp”. 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/~jds
Updates on the progress of all the comets will be posted in the SPA
ENBs. I’m 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 I’m there and there is a chance that I’ll be able to update
the web page during my absence.
Jonathan Shanklin