Ordinary Meeting, 2002 November 30
The December Sky
Mr Mobberley opened with a report of the occultation of a mag 5 star, HIP 19388, by minor planet 345 Tercidina on 2002 September 17. The speaker illustrated the location of amateurs who had contributed observations from across central Europe, and hailed it as the second most observed occultation of its kind – the first being a US event. These observations had placed more than 60 chords across the object, and refined its size to 99km by 93km. Mr Mobberley remarked that professionals would have been unable to obtain such accurate data without the use of a costly space probe.
During 2002, there had been an unusual clustering of four nova events in Sgr, one of which had peaked at mag 5. The speaker showed Mike Jäger's images of the second event, V4742, which was tucked just south of the Trifid and Lagoon nebulae. The nova showed a striking red colour, and Maurice Gavin had reported spectral measurements of a strong Hα line. A light curve constructed by Guy Hurst showed a three magnitude fall within a few days of the peak at 8.5 around 17 September. The third Sgr event, V4743, had been discovered by Katsumi Haseda on September 20 at mag 5.
A GRB on the evening of October 4 had been the first ever to have been successfully observed by amateurs. The object, GRB021004, appeared beside the Eastern side of the square of Pegasus. Nick James had achieved the first amateur images at twilight, followed by numerous others. A robotic telescope had obtained images of the optical transient associated with the event within minutes of its discovery.
The speaker congratulated Mr Tom Boles on a spate of supernova discoveries, starting with 2002gc. Three further discoveries had come within a week, including 2002hl and 2002hm, which had received consecutive labels from the IAU. The absence of any further discoveries since November 7 was most disappointing, however! The hypernova 2002ap in M74 was still observable at mag 10.7 after 10 months.
Moving onto planetary observation, Mr Mobberley showed fantastic images by Ed Grafton from Houston and Damian Peach from Tenerife. A notable white spot in the South Temperate zone of Saturn had caught the attention of both on September 27. More generally, recent images had revealed a greenish tint to Saturn's southern polar region, and a greyish tint had also been reported in the A ring.
Recent images suggested Jupiter's Great Red Spot to be a little more orange than usual. An exquisite stacked image of the post-spot turbulence by Ed Grafton was of exceptional quality. The inclination of Jupiter's orbit was particularly favourable for so-called "Mutual Galilean Events" in the coming month. These are events where two moons occult one another. The speaker referred interested observers to a very complete article in the 2002 December Sky and Telescope,2 and listed the observable UK events: Dec 16th, 2h07 – 2h13, Callistro totally occulting Io for 54 seconds; Dec 20th, 4h48 – 4h55, Europa eclipsing Io over a period of 112 seconds to a maximum of 59%; Dec 23rd, 0h15 – 1h18, Europa eclipsing Ganymede for 634 seconds to a maximum of 59%. There would also be occasions when two moons would cast simultaneous shadows onto the Jovian surface: Dec 17th, 2h02 – 2h17; Dec 24th, 3h55 – 4h53; Dec 31st 5h48 – dawn (7h29).
Damian Peach had recently turned his attention to Venus, in an attempt to image the mysterious Ashen Light. He hoped that three dimensional surface plots of his data would aid his quest, but he was without positive observation thus far.
Mr Mobberley opened his discussion of the comet scene with superb images of 2002 O4 (Hoenig) and 46P (Wirtanen) by Ed Grafton. The speaker illustrated the paths of 2001RX14 (LINEAR), which was expected to peak around mag 11; 2001HT50 (LINEAR-NEAT), which would pass through Hydra in December at around mag 12; 2002V1 (NEAT), which would brighten from mag 14 to 12 whilst passing through Aries in December; and finally 154P/Brewington which would brighten from mag 13 to mag 11 over the next three months. Currently in Aquarius, it would have a close encounter with the south-east limb of the square of Pegasus next February.
The speaker closed his summary with mention of the total solar eclipse of December 4, which would be visible across southern Africa and Australia. Many amateurs not present at the afternoon's meeting were preparing for this event, although totality would last only 26 seconds for Australian observers. Mr Mobberley then handed over to Neil Bone, who would summarise the results from the recent 2002 Leonid meteor shower.