Ordinary Meeting, 2005 May 25


The May Sky

Mr Mobberley opened by remarking that despite solar minimum being near, images of the Sun (from appropriately filtered instruments) still showed some substantial features; he showed a large sunspot group imaged by Nigel Bryant on April 30, and a prominence caught by Maurice Gavin on May 15 with his 40 mm Coronado PST. Then, turning to the UK supernova patrol scene, he reported that the recent lull still continued, and that, after a complete lack of discoveries this month, the UK total still stood at 170.

He next reported that radio galaxy 3C 454.3, lying just west of the Square of Pegasus, ~3° north-west of Markab, had, on May 9, been detected in an unprecedented outburst from its normally tranquil state, reaching mag 11.9 in the red-band, and 12.5 in the V-band. It was believed to be a blazer – an active galaxy viewed down the direction of one of its jets – an identification supported by observations of nearby knots of material which, due to an effect most apparent in blazers called relativistic beaming, appeared as if they were travelling at 14 times the speed of light.

There were still no visually observable comets: 2004 Q2 (Machholz) remained the brightest northern object at mag 9, still circumpolar in Canes Venatici, where it would remain until sinking southward into Boëtes in mid-July. On June 9 it would pass within 30' of the tight spirals of M94, when the Moon would be a favourable three days old; the speaker thought this might make a photogenic conjunction. 161P/Hartley-IRAS was in Pisces at mag 12 and brightening; it would pass into Andromeda on June 6, Perseus 11 days later, and then Cassiopeia on June 27, perhaps reaching mag 9 by that time.

Mr Mobberley mentioned two recent comet discoveries; firstly, P/2005 JQ5 (Catalina), found by the Catalina Survey on May 6. Its unusual designation resulted from its having originally appeared asteroidal in its discovery images. At mag 14, it was now showing cometary features, and might approach mag 12 by late June. In eastern Virgo at present, it would track westward and pass into Leo on June 19. The other discovery, 2005 K1, had been found by Brian Skiff at the Lowell Observatory using the 59 cm LONEOS Schmidt telescope. Presently at mag 17 in Draconis, it had originally been thought that it might brighten substantially, but refined orbital parameters placed its perihelion at a distant 4 AU from the Sun. It was reported to have a 12" coma, and 90" tail.

9P/Tempel 1 lay in Virgo, heading southward and brightening at mag 11; the speaker reminded members that it might flare substantially on July 4 after NASA's Deep Impact collided it with a 370-kg impactor, but that a clear southern horizon would be needed to see it: its unfavourable position placed it to set into the evening twilight shortly after the Sun on the following days. 21P/Giacobini-Zinner, at mag 11, was soon to pass from Andromeda into Pisces, but was fast heading eastward into dawn twilight.

Minor planets Ceres and Pallas had both recently passed their oppositions, on May 11 and April 27 respectively. Both had reached nearly mag 7, becoming easy binocular targets. Mentioning two occultations which had taken place in the last week, the speaker reported that 7 Iris' occultation of HIP 83097 on May 22 was not thought to have produced any observations, thick cloud covering most of its path. That of mag 11.4 star TYC 6238-01428-1 by 168 Sibylla on May 20 had met better weather, and, from the three observations of which he was so far aware, he showed the three resulting chords which constrained its size. It was placed at around 95 × 160 km, if an elliptical shape was assumed.

Jupiter, in Virgo, now transited at 9pm BST. Imaging maestro Dave Tyler had been observing it as early as possible in the evening to catch it at its highest in the sky; some of his finest results had come with the Sun only 1-2° below the horizon. A montage by John Rogers of many of the presently observable spots was displayed, special mention being given to a jetstream spot in the northern Southern Tropical Belt, which had approached the Great Red Spot (GRS), becoming irresolvably close to it. Later, there had been signs of a new feature within the GRS. A gallery of some of Mr Tyler's finest results followed.

Saturn's apparition was now past its prime, it now transiting at 4.30pm BST and setting just after midnight. The speaker displayed some recent highlights from Cassini, including a series of images of the F ring as Prometheus, one of its two shepherd moons, skirted its inner edge; it could be seen to visibly kink in the moon's wake. Mars was now rising at 2.30pm BST, in dawn twilight, but would soon be visible earlier in the night, its disk due to reach nearly 20" in the autumn, and its declination a UK-favourable +15°, exceeding +20° in early 2006.

Mr Mobberley closed with a slideshow of images by Damian Peach, who had recently returned from a 21-day trip to the steady skies of Barbados with his Celestron 9.25". Mr Peach had had clear skies on 19 of those nights, though he had found that they could yield to rainstorms with astonishing speed, making it vital to have rain covers close at hand at all times. He reported that the seeing had frequently reached Pickering 9-10 – so fine that after stacking and enhancing his best frames, he had found that features on 0"4 scales could often be seen, surpassing the instrument's 0"5 diffraction limit. A series of astounding lunar images was followed by a preview of his planetary images – the speaker explained that much was yet to come, as Mr Peach had returned with 400 Gb of images, and the task of processing them all would take some time to complete. Among his early results, features on Mars' disk had been remarkably well resolved, despite its diameter having been a mere 6"6 at the time of imaging. Mr Mobberley promised that the slideshow would continue next month, with the latest fruits of Mr Peach's massive image processing task.

After the applause for Mr Mobberley's summary, the President welcomed the evening's final speaker, Dr Jeremy Shears.






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