SPA Comet News, January 2004

The autumn gave generally favourable observing conditions and there were several comets on view, although all were initially very faint and only visible in large apertures. Two brightened to binocular levels, though the rest remained telescopic objects. Of the brighter pair, one has gone, but the other is still brightening, although by the time you read this there will be only a few weeks left in which to observe it. After that you will need to wait until May, for what may be a spectacular comet.

Comet 2P/Encke put on a fairly good show during the autumn, reaching about 6^th magnitude before it became too low to observe from UK skies, though so far I’ve received few reports from SPA members. I was able to recover it with the 30cm Northumberland refractor of the Cambridge University Observatories on October 19 and it slowly brightened over the next few days. I was surprised to see a report on the Internet that it was around 10^th magnitude on the same day that I had estimated it at 12.4 in the big refractor. The next evening I drove out to a dark sky site and was astonished to find it easily visible in 20x80 binoculars at magnitude 9.9. This clearly shows the benefits of having a good observing site, and sadly the outskirts of Cambridge and many other locations no longer are, so it is worth making the effort to travel. It also shows that large apertures don’t necessarily do best with very diffuse comets such as comet Encke. CCD observations can also give a very misleading picture and several CCD reports on the Internet were quoting the comet at 13^th magnitude or fainter, when it was visible in binoculars. I strongly encourage all observers to continue visual studies, particularly of short period comets that have been seen at many returns, as this is the only way of comparing historical apparitions with the current behaviour of comets. From Cambridgeshire a long run of cloudy skies at the beginning of December prevented me from following comet Encke as it brightened to 6^th magnitude, though I was able to just glimpse it in very transparent skies on December 7^th. A few observers from more equatorial locations managed to recover it in the early morning skies late in December. All in all it was a typical apparition of the comet, which showed an absolute magnitude comparable to that seen at each return over the last 50 years.

2002 T7 (LINEAR) brightened to binocular levels in December and was a fine sight through the telescope. Quite unusually it showed significant tail development, whilst still over 2 AU from the Sun, confounding what I said in the last newsletter. The visibility of the tail may have been enhanced because we were close to the orbital plane of the comet and it will be interesting to see if the tail continues to be prominent. The comet brightens fairly slowly, but will possibly reach naked eye brightness by the time it gets too far south for us to observe in mid March 2004. There are now a good number of observations in and although the comet is still some distance from the Sun as I write, it seems likely that it will reach 0^th magnitude in mid May. The only problem is that by that time it is a southern hemisphere object and we have no chance of seeing it.

We must 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. The current predictions suggest that it will be about 3^rd magnitude, however at the moment it is further away than 2002 T7 and so far all observations have been telescopic. Once comets get into binocular range they often appear brighter, as noted with comet Encke, so there is room for improvement. We may pick up comet 2001 Q4 in the twilight on May 7^th, but the tail will be nearly parallel to the horizon and not that easy to see, though it could be 10° - 25° long. Observing circumstances quickly improve and by mid month the comet is in Cancer with the tail running towards Regulus. The moonless window closes on the 19^th, when it should still be 4^th magnitude and it soon becomes circumpolar allowing all night observation. If you decide to travel to the southern hemisphere in May there is a rare opportunity to see two naked eye comets at the same time, although the range of latitudes in which you can do this is rather limited.

A further comet that should be getting towards binocular visibility around this time is another of over 130 discovered by LINEAR, 2003 K4. This one should reach 6^th magnitude over the summer and is well placed for observation. Sadly the circumstances of the return are poor and the comet is on the far side of the Sun when it reaches perihelion, though this does mean that it will pass through the SOHO coronagraphs field of view.

For more information on current comets and the latest updates on comets 2001 Q4 (NEAT), 2002 T7 (LINEAR) and 2003 K4 (LINEAR) see my web page at http://www.ast.cam.ac.uk/~jds Updates on the progress of these comets will be posted in the SPA ENBs. I will be in Antarctica until the end of March and hope to get an early sighting of comet 2001 Q4, though it will probably still be a binocular object. I think that I should be able to update the web pages during my absence on this occasion, as a new satellite data link should be up and running so I’ll try and keep you up to date with the latest developments.

Jonathan Shanklin