Ordinary Meeting, 2009 December 12


The Winter Sky

Dr Moore opened his Sky Notes by remarking that the International Space Station (ISS) would be making a series of early-morning passes over the UK in the coming week, and that it had grown increasingly bright over recent years as various solar panels and modules had been added to its structure. At 6.10am on the morning of the meeting, he had himself observed a pass for which the Heavens Above website1 had forecast a peak magnitude of –2.4, but in view of its having been quite readily visible through moderately thick cloud, he wondered whether it might not actually have been somewhat brighter.

On a related theme, the appearance of a strange spiral pattern of blue light in the Norwegian sky in the early morning of December 9 had attracted considerable attention in the media. The light show was now widely believed to have resulted from the malfunction of an experimental Russian Bulava ballistic missile, which Moscow had confirmed to have been launched from a nuclear submarine on the same day. The speaker commented that even if the test had failed, few would know where to begin if tasked with creating such an unusual geometric display of debris.

Turning to the solar system, Dr Moore reported that the Moon had been attracting interest in recent months on account of its having been deliberately impacted by a projectile on October 9 as part of NASA's LCROSS mission. The aim of this had been to throw up a large plume of material which could be studied spectroscopically to look for evidence for the presence water. At a press conference on November 13, NASA scientists had reported that clear evidence had been seen for a significant abundance of water. The speaker noted that this impact had come almost exactly 50 years after the first impact of a manmade spacecraft onto the lunar surface, that of Luna 2, on 1959 September 13.

In the coming month, Full Moon would be on 31st December and would be accompanied by a partial lunar eclipse, though even at the moment of greatest eclipse at 19h22 UT only 8% of the lunar disk would be in shadow. The eclipse would begin at 17h17 UT and end at 21h28 UT. Of perhaps greater interest was the annular solar eclipse which would be visible two weeks later on 2010 January 15, and which would be best seen from the Indian Ocean or Africa. The Sun remained otherwise quiet in its extended period of solar minimum, and despite the appearance of a small sunspot on December 10 its disk remained entirely blank for most of the time.

Two notable meteor showers would reach maximum within the next month. The Geminids, already under way and due to reach maximum on December 14, promised to provide a very spectacular show as already described by the previous speaker. The Quadrantids were less favourably timed, reaching maximum on December 3, when they would have to share the sky with an 18-day-old Moon. However, the speaker commented that given the poor predictions, it was likely that a relatively small number of observers would monitor them, and so any observations that were made would be of particular importance.

Turning to the planets, Dr Moore reported that Jupiter's current apparition in the southern skies had passed opposition on August 14 and was now nearing its end. As seen from the UK, the planet now set at around 8pm. On December 19, it would reach a close conjunction with Neptune, which would pass within a mere half-degree to its north. With Jupiter shining at mag. –2.1, and Neptune at a mere mag. 7.9, the former might prove a useful pointer for finding Neptune, though only for those with particularly unobstructed western horizons. Mercury would reach greatest eastern elongation in the evening sky of December 18, though it would prove a difficult object at this apparition, setting at 5.07pm, four degrees below the two-day-old Moon.

Saturn's new apparition was now underway. It was currently a morning object and would remain so for a few more months until reaching opposition on 2010 March 22. By Christmas, however, it would be making it above the horizon by midnight. Its rings remained in a relatively closed configuration, currently inclined at 4.8° to our line of sight, and over coming months this would not improve. Rather, the rings would appear to narrow once again, and by June would be inclined at a mere 1.7°. They would not begin to open out any further than their present configuration until the autumn of 2010.

Mars could be found in Cancer and would be the planet of interest in the coming weeks. It would reach opposition on January 29, two days after making closest approach to the Earth on January 27, on which occasion it would appear at its largest. However, it was in a comparatively distant part of its orbit at this apparition, and its disk would consequently measure a rather meagre 14" across at its largest. For comparison, it had measured 25" across at its 2003 opposition, and Jupiter typically measured around 50" across. Dr Moore commented that Mars could be quite a challenging planet to observe visually, since it appeared as a small and very bright disk whose glare could hinder the observer from distinguishing much detail in its disk. He added that its rotation period of 24h39m – only a little longer than an Earth day – was a frustration to those who observed at a similar time each day, as for many days at a time the observer would see a very similar face. This was an especial frustration, he added, as the hemisphere around Syrtis Major was rather more visually appealing than the comparatively bland appearance of the opposite hemisphere. He advised visual observers to use a red filter when studying the surface of the planet, and a blue filter when studying the polar cap.

Turning finally to the deep sky, Dr Moore congratulated Ron Arbour upon having made his 22nd supernova discovery, 2009mf, in IC 65, on December 6. The discovery had been made using Arbour's 12-inch Meade. Dr Moore also congratulated Tom Boles upon having made his 127th supernova discovery, 2009kp, in NGC 6246, on November 3; this was Boles' tenth discovery of the year.

The midnight sky in December was commonly associated with the constellations of Gemini, Orion and Taurus, and so the iconic Great Orion Nebula (M42) would be sure to be well observed in coming weeks. But the speaker also urged the audience to take a look at the nearby bright nebulous complex of NGC 1973, NGC 1975 and NGC 1977, as well as M43, just to the side of M42, and the open clusters NGC 1980 and NGC 1981 at either end of the Orion's sword. A little more challenging were the planetary nebulae Abell 12, close to μ-Ori, and NGC 2022, both in Orion. The open clusters M36, M37 and M38 in Auriga were also extremely appealing; NGC 2169 was a more challenging target, shaped like the digits '37'. Finally, the speaker added that Hubble's Variable Nebula (NGC 2261) was well placed at present in northern Monocerus and provided an unusual opportunity to see an emission nebula which could change quite radically in appearance over a period of months.

Following the applause, the President adjourned the meeting until 5.30pm on Wednesday January 27 at the present venue.


Dominic Ford




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