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Circular 2005/2

Tim Cooper
Director: Comet & Meteor Section
2005 June

The second half of 2005 brings some interesting observing opportunities for both comet and meteor observers, including the Deep Impact probe crashing into comet Tempel 1 on July 4.

Firstly some feedback. I received a good number of observations of the Geminids in December. The results were written up in an article 'Observations of the Geminids in 2004' which will appear in the June 2005 issue of MNASSA. Several observers also managed some good results on the eta Aquarids in May 2005. These results have been sent to the IMO for processing into the global database. Also a good set of data was obtained on comet Machholz C/2004 Q2. The results and analysis will also be published in the June MNASSA as 'Another Naked Eye Comet in 2004 – Observations of Comet C/2004 Q2 Machholz' .

Many thanks to the following observers who contributed to these results: Mike Begbie, Tim Cooper, Kos Coronaios, Dudley Field, Brian Fraser, Trevor Gould, Tony Jones, Karen Koch, Gerrit Penning, Michael Poll, David Pringle-Wood, Auke Slotegraaf, Magda Streicher, Cliff Turk and Koos van Zyl.

I think all of the above are ASSA members, and receive MNASSA. If not let me know and I will forward a copy of the results.

Comets

Comet 9P Tempel

Mike Begbie, Magda Streicher and myself have been following this comet since early May. The brightness has changed little during the intervening period, and the comet is still around magnitude 11, considerably fainter than predicted. In 2005 the comet passed close approach in late April at delta=0.71 AU, very similar to delta=0.69 in April 1994 when it reached magnitude 9.6 shortly after close approach. It will likely fade slowly after perihelion in early July. However, one event is still to take place, the results of which are unpredictable – the Deep Impact probe. As part of this mission a 370kg copper projectile is due to impact comet 9P at 06h00 UT on July 4. The event will not be visible from southern Africa, where it will be daytime, and our first opportunity to see if the impact has had any visible effect will be as darkness falls later on that evening of July 4. I would urge all observers to observe the comet closely on the nights leading up to impact, and then immediately thereafter, paying attention to the comets brightness, size and condensation. Please let me have your observations on a nightly basis by email. CCD images of any jets or developments in the coma will be very welcome.

The comet was also imaged by Mauritz Geyser. His images are shown below, taken on April 11, and the image on the left is a good representation of how the comet appears in the telescope.

Comet C/2004 Q2 Machholz

After being well observed before perihelion passage, this comet moved too far north for observation in February. Mike Begbie has been following it recently as it starts to come into range again, still located near Ursa Major. It continues to move slowly southwards but is now very diffuse, magnitude 10 and fading.

Comet C/2003 T4 LINEAR

This comet crosses the constellation of Columba during June and July, likely fading from magnitude 9 to 11 as it does so.

Comet P/2004 V2 Hartley-IRAS

This comet may reach magnitude 9 in June or July around perihelion in its 21.5 year orbit on June 20. However, during June it moves rapidly northwards and will likely only be in reach of our Zimbabwe based colleagues until mid month.

Comet C/2005 A1 LINEAR

Is a morning object in western Pisces. It is magnitude 10 and fading.

Comet C/2004 B1 LINEAR

This comet reaches perihelion in February 2006. It may be visible in November at magnitude 10-11, passing very close to the south celestial pole (4 degrees on November 5).

Meteor Showers

Conditions do not favour the major meteor showers in the second half of the year. The delta Aquarids, Orionids, Leonids and Geminids are all heavily affected by the moon.

Conditions favour the July Phoenicids, a minor shower with peak activity around July 13. The shower is desperately in need of observations to determine its behaviour. Observe 2 or 3 days either side of maximum, by plotting all observed meteors. The waxing moon will be a problem before midnight, so observe in the early morning hours when the radiant is at its highest.

The alpha Capricornids are also favoured, with the moon only rising in the early morning. With the radiant highest just before midnight, you can observe in the evening until moonrise. The meteors are slow and often bright, with occasional fireballs. Be careful to sift out and report members of the other showers active at this time, including the delta and iota Aquarids and Piscis Australids. The best way to differentiate the showers is by plotting. Rates are generally around 5 per hour, but unexpectedly doubled this in 1995.

The Southern Taurids in November are part of a complex set of ecliptic showers which starts with the Southern Arietids, Northern and Southern Piscids, moving to the Northern and Southern Taurids, and then the Northern and Southern chi Orionids in December. This complex was described in detail in the April 2005 issue of the IMO journal WGN, and appears to be related to comet Encke as well as several minor planetary parents. This complex has its highest rates (about 5/hr) at the time of the Southern Taurids, but in reality there is probably no real defined maximum, and the peak rate probably 'floats' along the activity profile from year to year. Observation over several nights with plotting of all members is essential. Bright members and fireballs are common.

The waning gibbous moon does not favour observing the alpha Monocerotids. The shower is normally inactive, but showed brief outbursts in 1925, 1935, 1985 and 1995. In the latter case the outburst lasted only about half an hour but with rates approaching ZHR=400. Observations in 2005 to see if there is a periodicity of 10 years are essential despite the moon. Any possible outburst is predicted for 15h00 UT on November 21, whereas the radiant only rises around 22h00 SAST (20h00UT) locally. Please observe the night before and after predicted maximum, since even negative reports are of use, and will help define the background rate outside of any outburst.

Finally, please note:

I recently received a vociferous (and rather hurtful) email from one individual regarding the date quoted for meteor shower maxima in the Sky Guide Africa South. His complaint was that he was witnessing only 10% of the quoted rates because I had all the dates wrong by one day! The maximum date quoted for meteor showers is given as a guide, and may vary by 1-2 days either side, depending on the shower. It is not absolute and nor is it the law that the shower will peak on the quoted date. It is our job as meteor observers to observe showers over a period to determine their behaviour from year to year. Never restrict your observations to the quoted night of maximum only, and then decide the shower has not performed to (your) expectation. If you have queries, please ask!

Clear Skies

Tim