Ordinary Meeting, 2009 March 25

The March Sky

Mr James opened with a review of the current circumstances of the planets and other solar system bodies. He reported that the Sun was continuing to show little sunspot activity, and that despite the sporadic appearance of a few small sunspots from time to time, there were no signs as yet of the start of a new sunspot cycle. The Moon was not currently visible – it would pass New Moon on the following day, March 26 – but the coming week would provide an unusually good opportunity to observe its waxing phases. The speaker explained that at this time of year the ecliptic was highly inclined to the horizon at dusk, and this would place the Moon at an unusually high altitude in the early evening sky as it approached setting during its first few days; he predicted that the young crescent would be readily observable at nightfall within a couple of days. He added that the Society for Popular Astronomy would be organising a Spring Moonwatch between March 28 and April 5 in recognition of these favourable observing conditions, encouraging novice and experienced astronomers alike to look at the Moon in celebration of the International Year of Astronomy.

Turning to the planets, Mr James explained that Mercury would be coming up to superior conjunction on March 31, but would reappear in the evening sky in late April. He added that on the date of its maximum eastern elongation, April 26, it would appear within 3.5° of the Moon and the Pleiades; the triplet would appear at 10° altitude in twilight at 20h00 UT.

Venus was also close to the Sun at present, and would reach inferior conjunction on March 28; it would re-emerge in the morning sky over the next few weeks, reaching maximum western elongation on June 5. The speaker added that it was still just about visible in the evening sky, at a distance of 8.5° from the Sun, but emphasised that extreme caution needed to be exercised when observing an object so close to the Sun. It was essential that reliable setting circles be used to locate the planet and that observers did not attempt to navigate by eye. The reward, however, was a beautifully thin crescent. The speaker added that when Venus was in this phase, it was possible to use long-wavelength near-infrared CCDs to image thermal emission from the night-side of the planet, and that under the right conditions, such images appeared able to penetrate the planet's thick atmosphere to capture detail associated with features on its elusive surface.

The speaker added that he was personally hoping to follow Venus all the way through its current conjunction, and recalled how another member of the Association had once pursued a similar observing project using an 18-inch reflector, tracking Venus as it had passed, on that occasion, within 2° of the Sun. That member had reported seeing a complete ring of light being deflected around Venus' atmosphere at inferior conjection, but had also reported seeing a remarkably intense image of the solar disk reflected onto the roof of his observatory. Members were not recommended to try this at home.

Mars had passed solar conjunction in 2008 December, but would not reach opposition until 2010 January 29. It would be visible in the morning sky later in the year, but would remain a difficult object for the immediate future. Jupiter had likewise recently passed conjunction, but would reach opposition rather sooner, in August. Currently, it was only just beginning to become visible in the morning sky. Unfortunately, it would remain at rather southerly declinations throughout this year's apparition, and would not be well placed for UK observers.

Saturn was undoubtedly the best-placed planet at the moment. It had passed opposition in February, but would remain visible in the evening sky until late in the summer. The speaker mentioned briefly that, as had been discussed in several recent Sky Notes presentations, its rings were presented in an almost edge-on orientation at present: at the time of the meeting they were inclined at around 3° to our line of sight.

Mr James went on to report that an asteroid by the name of 2009 DO111, discovered by the Stewart Observatory on Kitt Peak on February 22, had generated some news headlines within the last few days on account of its having passed within a mere 1.22 lunar distances of the Earth on March 20 at 04h00 UT. This was a relatively large object by near-Earth-asteroid standards – around 100 m across – and had reached a peak magnitude of around 13. Peter Birtwhistle had obtained some excellent photometry of the object over the night of March 15/16, determining its rotation period to be 351.9±0.5 seconds.

Continuing on a theme of asteroids, Mr James reported that the Director of the Association's Meteor Section, Neil Bone, had recently been honoured by the International Astronomical Union (IAU), who had given an asteroid the name (7102) Neilbone. Mr Bone's citation for the honour had commended him for his contributions to amateur astronomy made though the Association, the Society for Popular Astronomy, and Astronomy Now magazine. The speaker warmly echoed this commendation and offered Mr Bone his personal congratulations. He added that the object itself was currently well placed for UK observation in Perseus, but would be a very challenging target at mag 18.3. Nonetheless, Dr Richard Miles had recently had little trouble obtaining images of it using the two-metre Faulkes Telescope North.

Turning to comets, Mr James reported that 2007 N3 (Lulin) had been the most exciting object of late; it had been an easy fifth-magnitude binocular target in the UK sky in February. He added that it had passed perihelion on January 10 and had made its closest approach to the Earth on February 21, reaching maximum brightness at around that time. It remained visible in the UK sky in Gemini, but was now fading fast. Whilst it was still possible to see it through binoculars, the speaker predicted that it would fade to telescopic magnitudes within 1-2 weeks.

Mr James closed by remarking that the best meteor shower of the next couple of months would be the Lyrids, which might reach a modest rate of around 10 meteors per hour on April 21/22. The waning Moon would present minimal interference, having only three days remaining until the New Moon of April 25.

Following the applause, the President adjourned the meeting until Wednesday May 27 at the present venue.

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Dominic Ford