Ordinary Meeting, 2009 May 27
The Sky in May
Dr Miles opened by showing a pair of time-lapse videos compiled by Gustavo Muler in Lanzarote, Spain, of the motion of comet C/2007 N3 (Lulin) relative to the background stars behind it. He went on to report that the Sun's period of quietness was continuing, and that although a small group of sunspots had been visible in the past month, these had now disappeared to leave the Sun's disk spotless once again. Modest prominences remained visible around the edge of the Sun's disk in Hα images. However, some astrophotographers had been finding some other uses for the Sun's disk: during the recent flight of the space shuttle Atlantis (STS 125; May 11–24) to service the Hubble Space Telescope (HST), French amateur astrophotographer Thierry Legault had captured the silhouettes of Atlantis and the HST against the solar disk as they approached one another on May 13 at 12:17 EDT.3 This remarkable image was a testament to Legault's skill and determination: the low orbit of the HST meant that the transit had only been correctly aligned within a 5-km-wide corridor of visibility, and had only lasted 0.8 seconds. In order to ensure a sharp image, Legault had used an exposure of a mere 1/8000th second.
In late April, the Moon had formed a pleasing conjunction with Mercury and the Pleiades (M45). Nick James had captured an impressive image of the triplet on April 26 in conditions of remarkably transparency; Richard Fleet had also captured a notable image of the triplet from Wiltshire on the following evening.
The speaker reported that Jupiter was coming into view in the morning sky, now rising at midnight BST. However, it would not be well placed for UK-based observers in its coming apparition on account of its southerly declination in Capricornus – currently –13° and reaching –16° by September. Saturn was now setting at around 2.30am BST, and would disappear into evening twilight over the course of the summer.
Moving out to Pluto, Dr Miles reported that the Association's Asteroids and Remote Planets Section would be organising an observing campaign over the coming months to measure the dwarf planet's lightcurve as it approached opposition on June 23. He reported that similar work had historically secured Pluto's rotation period to be 6.4 days, but that as Pluto was now moving further away from the Sun having passed perihelion in 1989 and having passed outside the orbit of Neptune in 1999, its surface temperature would now be dropping fast and its albedo features may have changed if any components of its atmosphere had begun solidifying onto its surface.
The speaker congratulated Tom Boles upon the recent discovery of his 120th supernova, 2009es, in IC1525 on May 24 – his first discovery since January. He closed his talk with some images that he had captured himself using the Faulkes Telescope South on May 14, a few hours after the launch of the Herschel and Planck space observatories aboard an Ariane 5 rocket from the Guiana Space Centre. These images had been taken shortly after the two spacecraft had separated from the Sylda 5 payload dispenser which had packaged them in the launch vehicle, and clearly showed three point sources. From their relative motion and relative brightnesses, the speaker reported that he had been able to identify each of them.
Following the applause, the President adjourned the meeting until the Exhibition Meeting, to be held at the Old Naval College Greenwich on Saturday 27th June.
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Dominic Ford