Ordinary Meeting, 2007 March 28


The March Sky

Dr Moore explained that he would begin his Sky Notes by talking about the Sun, and would then work outwards through the Solar System, concluding with the Deep Sky. He explained that the solar disk was quite featureless at the moment; its 11-year sunspot cycle was nearing its minimum. Solar Cycle 23 would shortly give way to Solar Cycle 24, which was expected to peak in around five years time. The coming cycle was forecast to be unusually active, with the possibility of significant disruption to communications satellites. On March 19 there had been a partial solar eclipse visible from East Asia and northern Alaska, though to the speaker's knowledge, no BAA members had travelled to observe it.

Mercury was poorly placed at present, despite its current evening apparition having recently passed greatest westerly elongation on March 22. It appeared highest in the sky at those times of year when the ecliptic was inclined as steeply as possible to the horizon at sunrise or sunset; presently, however, the ecliptic skirted close to the horizon. The next favourable opportunities to observe Mercury from northerly latitudes would be its morning apparitions in June and August.

Venus was much better placed; it was a magnificent mag –4 object in the evening sky. It was presently moving through Taurus and the speaker noted that it would pass within 3° of M45 on April 12; these might make an attractive pairing if viewed through binoculars. Venus would reach greatest elongation on June 9. The speaker warned members of the extreme danger of pointing telescopes close to the Sun whilst it was above the horizon; extreme care was necessary when observing either Mercury or Venus.

Mars was now rising just before dawn, and would steadily improve through the year, reaching opposition on December 24. Jupiter was disappointing at the moment; it rose at around midnight, but remained low in the sky throughout the night. It would reach opposition on June 5, but at that time of year the ecliptic was quite flat along the UK horizon at midnight, and so even then, Jupiter would have a typical altitude of only 17°; for comparison, its peak altitude in the UK sky during its 2002 apparition had been 44°.

Saturn, by contrast, was high in the sky, having recently passed opposition on February 10. Among recent highlights, it had been occulted by the Moon on March 2; a number of members had taken images, and the speaker praised especially those by Damian Peach. A second occultation would take place later in the early morning on March 29, albeit shortly after Saturn had set in the UK sky. Observers in these parts would, however, be able to see Saturn and the Moon drawing very close at around 3-4 am UT.

Another forthcoming occultation of interest would be that of mag 1.35 star Regulus on March 30; Regulus would disappear behind the Moon's dark limb at 03h30 UT and reappear from its bright limb at 04h19 UT. This would take place at low altitude – barely above 10° – but given the brightness of Regulus, it would be visible from even quite light polluted skies, given a good horizon.

Two meteor showers would be active in the coming month: the Virginids, peaking on April 10 with a ZHR of around 5, and the Lyrids, peaking on April 22 with a ZHR of around 10.

Two novae had been discovered within the past month, both by Japanese observers. On March 15, Akihiko Tago had discovered a mag 7.4 nova in Cygnus (V2467 Cyg), and then on March 19, Hideo Nishimura had discovered a mag 10.2 nova in Ophiuchus (V2615). Both of these, however, were low in the UK sky, and would be very tricky observing targets.

In the deep sky, this time of year was best known for the rich array of galaxies accessible in the evening sky: both the Virgo and Coma Galaxy Clusters were well placed. Directing a wide-field instrument at M84 (mag 9.1) and M86 (mag 8.9) – two of the largest galaxies of the Virgo cluster, separated by 17' – a vast number of NGC galaxies were visible within a single 1° field. The speaker also recommended M104 (mag 8.0) – the Sombrero galaxy – an edge-on spiral with dark dust lane, and NGC 4564 (mag 9.6) in Coma – perhaps the best non-Messier galaxy in the sky at this time of year.

To close, the speaker congratulated Mr Ron Arbour upon having recently discovered two supernovae in quick succession: SN 2007av in NGC 3279 on March 20, and SN 2007ax in NGC 2577 on March 22. The latter supernova was Mr Arbour's 18th discovery. The speaker noted that prior to these, Mr Arbour had gone for two years without any supernova discoveries; his last had been 2005au, which he had discovered on 2005 March 19. It was good to see him active once again.

The speaker then handed over to Mr Nick James, who showed a video of the recent total lunar eclipse of March 3. Dr Moore noted that this had been an exceptionally good eclipse: it had taken place at a sociable evening hour, and the sky had been clear across most of the UK throughout. Mr James explained that he would show a series of frames taken using a camera on a tracking mount. He had used a frame interval of two minutes during the partial phases, and one minute during totality. A total of 180 images had been taken. As a result of his tracking mount, the background starfield appeared stationary between frames, meanwhile the Moon moved across the field of view as it moved through the Earth's shadow. He remarked that these images provided a compelling illustration of how large the Earth's shadow was with respect to the Moon itself.

Following the applause, the President adjourned the meeting until April 21.


Dominic Ford




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