Ordinary Meeting, 2004 December 18

 

The December Sky

Mr Mobberley opened by expressing his very great honour to be presenting his Sky Notes this month in the presence of Sir Patrick Moore. As this was the last instalment of the year, he would follow his convention of opening with a round-up of the year's highlights. There had been 43 comet discoveries to date, including 15 by LINEAR, and a further 6 LINEAR co-discoveries. NEAT had contributed 5 discoveries. Though the competition was stiff, amateurs still had a chance, and there had been three such discoveries in 2004, by Bradfield, Machholz and Tucker. Mr Jonathan Shanklin interjected that a 44th comet had recently been announced.

Moving on to novae, the speaker reported that there had been six galactic events discovered in 2004, if one included Liller's October 28 event, which had strictly been in the nearby Large Magellanic Cloud. However, none of these had been particularly spectacular in the northern hemisphere. A total of 205 supernovae had been discovered, the LOSS search of the Lick Observatory being the most prolific discoverer with 80 events. However, the Association's Tom Boles and Mark Armstrong had the second and third greatest numbers of discoveries, with 22 and 15 respectively. Ron Arbour, also BAA, had made four discoveries. Mr Mobberley paused to reflect that given the UK skies, and the automated nature of the Lick search programme, British amateurs were doing astoundingly well.

Looking ahead, the speaker recommended observation of the Quadrantid meteor shower between 2005 January 1-6, expected to peak before dawn on January 3. Unfortunately the last-quarter Moon would interfere on this occasion, and whilst stressing he did not mean to put anyone off, Mr Mobberley added that he could only recall ever once seeing a single Quadrantid, though the shower had produced surprises on past occasions. On the same night, January 3, observers on the England/Scotland border would see a grazing lunar occultation of mag 3.9 star η-Virginis at 00h20 UT, at an altitude of 8° above the Eastern horizon. The speaker remarked that he normally ignored events so low in the sky, but given the brightness of the star in question, he thought this would be readily observable given a suitable site. London observers would see a near miss.

The speaker explained that his round-up of supernova discoveries would be exceptionally quick this month: there were no new UK discoveries, as there had been few breaks in the cloud. A new mag 7.6 nova had been discovered in Puppis by Tago and Sakurai on November 20, though it was now fading, and expected to plummet to mag 16 in the near future. Although it had been at the very southern limit of the UK-observable sky, the speaker showed an image successfully obtained in Chelmsford by Nick James at 03h17 on 2004 November 27 to prove that observation had been possible.

Moving onto comets, the next promising prospect was not far away in the form of C/2004 Q2 Machholz. Presently tracking northwards through Eridanus, and passing into Taurus on December 27, it was expected to peak at around mag 3-4 a week into January. Closest approach, at a distance of 0.35AU, would be on January 6, and it would pass around a degree to the west of the Pleiades the following night. The phase of the Moon was favourable, with New Moon on January 10 offering the chance of dark skies. On January 10/11 it would move through into Perseus, and on into Casseopeia on 26/27, fading to fifth magnitude by the end of the month.

Another of the 2004 amateur discoveries, Q1 (Tucker), would be in Andromeda for the next month, remaining close to mag 13, meanwhile Comet 78P/Gehrels, presently in Aries, would pass into Taurus in mid-January, tracking slowly eastwards through the constellation for three months at around mag 11, and passing close by Aldebaran in mid-March. An exciting prospect for the spring was 2003 T4 (LINEAR), passing from Hercules into Lyra around New Year, and perhaps brightening to mag 9 by the end of January. Looking ahead, it might brighten to mag 7 by early March, at which time it would be in Delphinus, heading towards perihelion at a distance of 0.85AU from the Sun on April 3. 32P/Comas Sola, in Aries until late March and fading, had now reached mag 11 and was essentially a CCD object, though likely to remain at mag 12 for the next few months.

With reference to the previous speaker, Mr Mobberley showed where in the sky to find 9P/Tempel, the comet which Deep Impact would be impacting next July. Brightening to around mag 15 by mid-January, and mag 9.5 by mid-June, whilst remaining in Virgo throughout, it would regrettably be too far south for UK observation by the time of impact.

Moving onto the planetary scene, the speaker reported that Saturn was now in Gemini, transiting at 2am, and so was up for most of the night. The northern hemisphere was slowly emerging from below the rings, and a selection of images from the Association's planetary imagers, including Dave Tyler, Damian Peach, and the speaker himself, were shown.

Members were reminded that before the next meeting, the Huygens probe would be released from the Cassini spacecraft, in orbit around Saturn, and would descend into the atmosphere of Saturn's moon Titan. The separation of the probe had been scheduled for 02h00 UT on Christmas Day, a time and date which the speaker thought sounded familiar from a certain recent Mars mission. Descent into Titan's atmosphere would take place on January 14, and hence it was possible that there might be images from the surface before the next meeting – if so, these would be the first such images from any moon in the solar system other than our own. Whether Huygens would land unscathed on the surface depended upon whether the probe survived impact, which in turn depended upon what material the surface was composed of – it was not presently known even whether to expect solid or liquid, as all images taken by spacecraft passing Titan had revealed nothing other than thick atmospheric clouds.

Jupiter was now in Virgo, transiting at 7am, and so was easily observable in the pre-dawn sky. Dr John Rogers, director of the Jupiter Section, had informed the speaker that the north equatorial belt (NEB) was very broad following a typical broadening event in 2004, and it was expected that dark 'barges' and bright 'portholes' would develop in the belt in the following year. The northern tropical belt (NTB) was still absent, and the southern tropical belt (STB) only present at some longitudes, such as those following the Great Red Spot, at System II longitude 100°. The speaker wished to draw members' attention to a forthcoming double Jovian Moon Shadow event on 2005 January 16, between 03h08 UT and 04h48 UT, at an altitude of ~30° in the UK, when both Io and Ganymede's shadows would be visible on the planet's disk.

On December 7, there had been a lunar occultation of Jupiter, though not visible from the UK as first contact was at 09h15 UT. However, Don Parker had returned a fine sequence of images of the ingress half of the occultation from Florida. Mr Mobberley wished to pass on Mr Parker's kindest regards to Sir Patrick Moore on the occasion of this significant anniversary.

To close, the speaker mentioned two asteroids which might be visible in the near future, firstly 3200 Phaethon, the progenitor to the Geminid meteor shower which had been on display in the days running up to the meeting. It would be around mag 15 in the Perseus/Pisces region throughout December, making closest approach at 0.61AU on December 22. 433 Eros, the asteroid which the NEAR spacecraft had imaged at close range and landed upon in 2001, would make closest approach next April, and although its distance would be 0.39AU, its physical size, 33×13×13km, would make it quite bright. Sadly, it would be at southerly declinations at this time, and so the best UK observing prospect would be in January, when Eros would be mag 11 as it plunged southwards. Finally, the speaker remarked that Hind's Variable Nebula in Taurus had been reported bright, and might be visible in 10-inch instruments. The reason for the brightening was uncertain, though thought to be connected with nearby variable star T-Tauri, 1' away.

Following applause, the President proceeded to welcome the next speaker, Dr John Mason.

Ashburn

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39.04°N
77.49°W
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