*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 254 2008 October 30 ==================================================== Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://www.popastro.com/ ORIONIDS - FIRST NEWS By Alastair McBeath, SPA Meteor Section Director As noted in ENB 253, the Orionid maximum was scheduled to happen on Monday, October 20, and early indications are Orionid rates were indeed above normal then, as hoped-for, and that they persisted for more than one night, just as in 2006 and 2007. Details are still being established, but preliminary reports on the International Meteor Organization website (IMO; available via the homepage at http://www.imo.net ) have so far suggested Zenithal Hourly Rates (ZHRs) of 30-40 from October 20 to 22, perhaps peaking around 40 on October 21. Initial SPA results indicated ZHRs of ~40-60 on October 20-21 and ~50-70 on 21-22, but these were based on few reports, and await confirmation. All values may have been affected by the bright waning Moon. Some early comments indicated brighter Orionids, with apparently very healthy fireball numbers (meteors of magnitude -3 and brighter), were spotted by a few lucky observers on October 19-20. Magnitude distributions for the shower on October 20-21 and 21-22 in SPA data suggest these were fairly normal by then however, even so, with the usual smattering of fireballs we would expect. Comments can be found on the SPA's Observing Forum, at http://snipurl.com/4oyb1, and also on the UK Weather World's Space Weather Forum, at http://snipurl.com/4oybv, where there is a fine Orionid image from October 21-22. SEPTEMBER METEOR ROUND-UP By Alastair McBeath & David Entwistle, SPA Meteor Section The bright-meteor outburst over North America on September 9, reported last time, was found remarkably weakly in the full set of September's radio results (see Radio Meteor Observation Bulletin 182 at http://www.rmob.org ). Comparing those datasets which did and did not show it may suggest that the outburst was due almost exclusively to bright meteors alone, and that smaller particles producing fainter meteors (which many radio meteor systems preferentially detect) were notably absent. Observer-analyst Jeff Brower from Canada has also asked us to correct his earlier note that his video system recorded 13 meteors of magnitude +1 and brighter between 04:12-12:26 UT on September 9, to 13 meteors of magnitude -1 and brighter, making the event still more remarkable! Nothing further has been established for the widely-seen September 22-23 fireball that may have come down partly over the Borders of Scotland regrettably, but hard on its heels came another event observed from multiple sites on September 25-26 around 20:55 UT. This was due to the re-entry of part of a Russian Proton rocket launched from Baikonur about twelve hours earlier on September 25. It was reported to us from six sites in south Wales, southern England, the Channel Islands and France, and was also imaged from southern England - see http://snipurl.com/4p014 , on the SPA's Observing Forum. It was seen from around ten other places in France (thanks to French meteor expert Karl Antier for this news). Four radio meteor observers, two each in England and France, recorded a strong signal probably due to it too. As with most re-entries, the event was unusually slow-moving for a meteor and long-lasting (in some cases for more than 30 seconds), and its long path carried it below the horizon for several witnesses in the British Isles. It peaked around magnitude -6, and some of the French sightings reported late-stage fragmentation too. The predicted ground track for the event (which helps explain the observers' locations) can be found at: http://snipurl.com/4p030 . EARLY OCTOBER METEOR ROUND-UP By Alastair McBeath & David Entwistle, SPA Meteor Section Continuing almost without pause from late September, the first ten days of October brought a fresh raft of items of meteoric interest. Among other fireballs (see the Recent Fireball Sightings webpage at http://snipurl.com/4p03x for the list of those reported to the SPA), there was a clutch of probably four bright to brilliant ones on October 5-6, each seen so far from just one place, around 18:28, 19:30, 20:08 and 03:10 UT. This date called to mind the bright-meteor events detected by European video observers on October 5-6 in both 2005 and 2006 (on which see most recently the report in ENB 206, at http://snipurl.com/4p0dw ). Whether the 2008 fireballs may have related to another return is uncertain. Only the 20:08 UT fireball was reported fully enough to suggest a possible radiant, which perhaps lay somewhere between Alpha Cephei and Alpha Cygni, on the opposite side of the pole to that near Draco's tail-tip implicated in the 2005 & 2006 events. Assuming any 2008 recurrence might have repeated within a similar interval to those two previous returns, it should have happened on October 5 around 13h-16h UT. October 7 brought a world's first event - the predicted atmospheric entry of an asteroid! Asteroid 2008 TC3 was discovered on October 6 during routine searching as part of NASA's Catalina Sky Survey for near-Earth objects, by the Mount Lemmon telescope in Arizona, USA. It was realised it would hit the Earth, but was small enough to ablate in the atmosphere and not strike the surface. It arrived close to its expected place and timing at around 02:46 UT on October 7 over Sudan in eastern Africa. The brilliant impact flash was claimed as spotted by the crew of a KLM airliner, and it was imaged by the Meteosat-8 Earth-observing satellite too. Comments and links to various webpages with further information (including the Meteosat impact image) can be found via the SPA's General Chat Forum at http://snipurl.com/4p0mc and http://snipurl.com/4p0mm , plus the UK Weather World's Space Weather Forum at http://snipurl.com/4p0nq . The Draconids seem to have produced nothing unexpected around October 8-10, based on visual results in to the SPA from Martin McKenna (Co. Derry), "JohnF" (London) and Assistant Director David Entwistle (Lancashire), plus video results from Enrico Stomeo in Italy. A few "possibles" were claimed, but at negligible levels. However, October 8-9 was notable for two further fireballs, one of magnitude -3/-8 at ~20:52 UT seen from Surrey and Worcestershire (see http://snipurl.com/4oyl4 on the SPA Observing Forum), the other of magnitude -6/-8 at 03:08 UT reported from four locations so far, in Lancashire, West Sussex, Belgium and Holland, from which latter it was imaged by Klaas Jobse's all-sky fireball patrol camera, as part of his routine monitoring for the European Fireball Network. A strong echo-signal in-time to this second meteor was also recorded by ten radio observers in Belgium, England and France. The earlier fireball may have flown on a roughly northerly to southerly track above eastern England, perhaps over Cambridgeshire to Kent, while the 03:08 one may have passed approximately southeast to northwest from somewhere high above or near Rouen in northern France, to end over the Channel some way WNW of Dieppe. Its image can be found on Klaas' website, at http://snipurl.com/4sau0 . As always, fresh meteor reports, including fireball sightings made from within or near the British Isles, are welcomed by the Section. Details to report can be found on the website, via the meteor homepage at: http://snipurl.com/4p052 . MAIN METEOR PROSPECTS FOR NOVEMBER By Alastair McBeath, SPA Meteor Section Director The long-lasting pair of minor Taurid showers continue until November 25, reaching maxima around November 5 (Southern Taurids - waxing crescent Moon) and 12 (Northern Taurids - full Moon), though the combined effect of both showers is to produce an almost plateau-like peak between these dates, with combined ZHRs of ~8-10 or so. Lower rates of these slow, often bright, meteors may be hunted for at other times during the month when there is no Moon, but as mentioned last time, 2008 sees the latest prediction for a 'swarm' return by David Asher of Armagh Observatory. This gives the possibility of unusual activity from the showers, perhaps from late October through till maybe mid November, or just at some stage in the first half of November. Previous 'swarm' returns in 1995, 1998 and 2005 have sometimes produced persistent ZHRs of ~10-15 through till November 10 (as in 2005) or increased numbers of fireballs (as in 1995 and especially 2005). Even the brightening Moon towards mid month may not spoil too much of the show if another relatively fireball-rich return happens, but don't expect too much. For example, the 1998 return produced ZHRs of ~8-10 only between October 27-31, and without more fireballs than normal, so only an examination of carefully-made observations later revealed what had really occurred. Although the run of strong to storm Leonid returns seen from 1998-2002 is unlikely to repeat again until the 2030s (or perhaps even till next century), independent model calculations by Russian Mikhail Maslov and Frenchman Jeremie Vaubaillon have indicated 2008 may bring good to strong activity. Various possible maxima and strengths have been proposed. On November 17, UT timings include around 00:22 (Maslov; ZHRs ~130?; brighter-than-average meteors?), 01:32 (Vaubaillon; dust trail left by the shower's parent comet 55P/Tempel- Tuttle at its 1466 return; ZHRs very uncertain, maybe ~50, perhaps between ~25-100?) and 09h ('traditional' peak time based on when the Earth passes nearest the node of the comet's orbit; ZHRs ~15-20?). On November 18, Jeremie Vaubaillon has suggested we may encounter the Leonids' 1932 dust trail at about 21:38 UT, perhaps with ZHRs of ~20. None of these predictions is guaranteed, of course, nor can other unexpected peaks be ruled-out! The waning gibbous Moon around Gemini-Cancer on November 17 & 18, is about as badly-placed as possible for observers, especially because the shower's radiant rises only by ~23h UT, and reaches a fully usable elevation after midnight from Britain. Observers trying to catch whatever the Leonids produce this time will simply have to brave the Moon and hope for the best, primarily on November 16-17 if you are watching from the British Isles. Cover as much clear sky as you can comfortably see, but face away from the Moon, or block it behind some obstruction like a rooftop or wall. The shower is active from November 10-23, though the lower rates likely away from the peak night(s) may well pass unnoticed in the moonlight. Expect very swift, often trained, meteors. For more on November's likely meteor activity, plus radiant charts for the Taurids and Leonids, see the monthly meteor page on the SPA website, at: http://snipurl.com/4oymf . Good luck, and clear skies! COMET NEWS By Jonathan Shanklin SPA Comet Section Director Comet 2008 A1 (McNaught) is slowly moving into UK skies. Although 8th magnitude it is low down in the evening sky, and a difficult target for large binoculars. Over the coming weeks it will slowly fade, and only becomes slightly better placed for viewing. Although fainter, comet 2006 W3 (Christensen) is better placed for viewing, lying high in the northern sky. Currently 10th magnitude and still 4 AU from the Sun, it will continue brightening and may reach 7th magnitude when it reaches perihelion at 3.1 AU in 2009 July. 85P/Boethin, for which an ephemeris appears in Popular Astronomy, has still not been recovered at this apparition. It seems quite likely that it was discovered when in outburst, and has possibly disintegrated. However as we saw with 17P/Holmes, comets can do surprising things, so it is worth keeping an eye out for developments. Finder charts can be found at: http://snipurl.com/4oy8k NO ICE ON MOON AFTER ALL? New Scientist A decade ago, the Lunar Prospector spacecraft suggested that the Moon's poles have large concentrations of hydrogen near the surface, which could be in the form of frozen water deposited by comets. That would be very useful for a possible future base on the Moon, providing water for astronauts and hydrogen fuel for their vehicles. The Shackleton Crater at the south pole has been a prominent candidate for a future base station, since it contains a ledge on its rim that would be a good landing spot. If the crater were also to hold frozen water, it would be an excellent location. But that possibility seemed to evaporate when radar signals formerly attributed to water-ice were also found to reflect off sunlit areas where ice could not survive. So it had been hoped that the Japanese spacecraft Kaguya, which was launched in 2007 September, could shed light on the question by observations from lunar orbit. The spacecraft contains a camera that can obtain images of the Moon's surface even in the near-total darkness of its south pole. The inside of the crater receives no direct sunlight, but for a short period during summer time in the Moon's southern hemisphere (November and December in the Earth's calendar), a small part of its rim catches some sunlight, which is then scattered to the crater floor. Japanese scientists analysed pictures of the crater taken at such a time. The images resolve objects as small as 10 metres across. They provided a full profile of the crater, including details of tiny craters on its floor and two landslides from the inner wall. The most striking feature was what was missing. If there had been ice, there would have been brighter reflections from its surface, but none was visible. Instead, the images showed just dull lunar soil. That does not completely rule out the possibility of frozen water within the crater -- it could be buried, or the ice crystals could be dirty and mixed with particles of soil. But there may be no water at all, and the hydrogen could be combined in another compound like methane. Ice particles trapped within the lunar soil could still be useful for a human base station, but that would depend on the difficulty of mining the mixture and extracting the water. PHOBOS PROBABLY MADE OF RUBBLE ESA Mars has two small moons. The larger one, Phobos, is an irregular lump of rock measuring 27 by 22 by 19 kilometres. It has been observed in a series of close encounters by the Mars Express spacecraft, and is now considered almost certain to be a rubble pile rather than a single solid object. The pictures taken by the spacecraft enable an accurate 3-dimensional model of Phobos to be made, so that its volume can be determined with some precision. During one of the nearest encounters, the spacecraft's radio signals were monitored from the Earth to record the changes in frequency brought about by Phobos' gravitational acceleration of Mars Express, to enable the calculation of the precise mass of the moon. When the team has finished doing the sums putting the mass and volume data together, it will know the density, which will be an important clue as to how the moon was formed. Previously, radio tracking from the Soviet Phobos 88 mission and from other spacecraft orbiting Mars had provided the most accurate mass. The team's current mass estimate for Phobos is about one-billionth the mass of the Earth. Preliminary density calculations suggest that it is 1.85 grams per cubic centimetre, which is very similar to that of some asteroids. Asteroids that share Phobos' density are known as D-class. They are believed to be highly fractured bodies containing caverns and voids because they are not solid but are just collections of pieces weakly held together by gravity, 'rubble piles'. Spectroscopic data from Mars Express and previous spacecraft show that Phobos has a composition similar to that of such asteroids. That suggests that Phobos, and probably Deimos too, are captured asteroids. However, one circumstance remains difficult to explain in that picture: usually, asteroids are captured into just random orbits around the planet concerned, but Phobos orbits above Mars' equator -- a very specific case. OUTER SOLAR SYSTEM NOT SO CROWDED Harvard-Smithsonian Center for Astrophysics The Taiwanese-American Occultation Survey (TAOS) spent two years periodically photographing portions of the sky to look for small bodies orbiting beyond Neptune, in a region of the Solar System called the Kuiper Belt. The survey looked for Kuiper Belt objects (KBOs) with sizes between 3 and 28 kilometres. Since such objects are too small to see directly, the survey watched for stars to dim as KBOs passed in front of and occulted them. After accumulating more than 200 hours of data (only 100 hours' work a year, a duty cycle of little over 1%) watching for stellar flickers lasting a second or less, TAOS had not observed any occultations. The Kuiper Belt contains objects in a range of sizes -- a few large ones (the 'dwarf planets' Pluto, Eris, Makemake and Haumea) and many more smaller ones. The commonness of a given size might offer a clue as to the history of planet formation and dynamics. In particular, the size distribution of KBOs may reflect a history of agglomeration, in which colliding objects tended to stick together, followed by destructive collisions, where collisional velocities were high enough to shatter the rocks involved. Astronomers wondered whether they would find more and more objects at smaller and smaller sizes, or whether the distribution levelled out. Unless there has been some miscalculation over the sensitivity of the TAOS observational procedures, the fact that no occultations were seen sets an upper limit to the number density of KBOs in the relevant size range. The outer Solar System now appears not to be as crowded as some theories suggest, perhaps because small KBOs have already stuck together to form larger bodies or frequent collisions have ground them down into even smaller bits below the threshold of the survey. PLANETS IN COLLISION? UCLA Astronomers have been studying a star known as BD +20 307, which is in the constellation Aries and is surrounded by about a million times more dust than exists around our Sun. They expected BD +20 307 to prove to be a young star, with the massive dust ring signalling the final stages in the formation of a planetary system. A major revision of ideas was called for last May, when Carnegie astronomers showed that BD +20 307 is actually a close binary system, composed of two stars, both very similar in mass, temperature and size to our own Sun, orbiting about their common centre of mass every 3.42 days. The patterns of element abundances in the stars indicate that they are several billion years old, like our Solar System. The origin suggested for the extraordinary quantity of dust, orbiting the binary pair at about the same distance as Earth and Venus are from our Sun, is a collision between two terrestrial planets. That would have had to have happened quite recently by astronomical standards, no more than a few hundred thousand years ago, because at such distances from a star small dust particles get pushed away by stellar radiation while larger pieces get reduced to dust in collisions within the disc and are then pushed away. A serious objection to the idea of a major collision is, however, that it seems most unlikely that bodies that have orbited stably for billions of years would suddenly decide to collide vigorously just now, but no more plausible idea has been put forward so far. MASSIVE DOUBLE STAR SYSTEM ESO A new image of the star-forming region Gum 29 shows that a small cluster of stars, only 1 to 2 million years old, called Westerlund 2 includes one of the most massive double-star systems known. Gum 29 is a region of hydrogen gas that has been stripped of its electrons (ionised) by the intense radiation of the hot young stars at its centre. Astronomers call that an HII {'aitch-two') region, and this particularly fine example is over 200 light-years across. The latest measurements indicate its distance as about 26,000 light-years, placing it towards the outside edge of the Carina spiral arm of the Milky Way. Previous observations have shown that a pair stars on the south- preceding side of the cluster are particularly massive. They have masses of 82 and 83 times that of our Sun and orbit one another in approximately 3.7 days. They are both Wolf-Rayet stars -- massive stars nearing the end of their lives, expelling vast quantities of material as their swansong. X-ray observations show that streams of material from each star continually collide, creating a blaze of X-ray radiation. FIRST GAMMA-RAY-ONLY PULSAR NASA A pulsar is a rapidly spinning neutron star, the crushed core left behind when a massive star explodes. Astronomers have catalogued nearly 1800 of them. Although most of them have been found through their pulses at radio wavelengths, some also beam energy in other forms, including visible light and X-rays. Now the orbiting Fermi gamma-ray telescope has discovered a pulsar that seems to pulse only in gamma-rays. The object lies within a supernova remnant known as CTA 1, about 4600 light-years away in the constellation Cepheus. It emits 1000 times the energy of our Sun. and its lighthouse-like beam sweeps across the Earth every 316.86 milliseconds. Fermi scans the entire sky every three hours and detects photons with energies ranging from 20 million to more than 300 billion times the energy of visible light. The instrument sees only about one gamma-ray per minute from CTA 1, but that is enough for scientists to piece together the neutron star's pulsing behaviour, its rotation period, and the rate at which it is slowing down. A pulsar's beams arise because neutron stars possess intense magnetic fields and rotate rapidly. Charged particles stream outwards from the star's magnetic poles at nearly the speed of light to create the gamma-ray beams Fermi sees. Because the beams are powered by energy drawn from the neutron star's rotation, the pulsation period gradually increases as the neutron star spins down. In the case of CTA 1, the rotation period is increasing by about 12 microseconds a year. The SPA Electronic News Bulletins are sponsored by the Open University. Bulletin compiled by Clive Down (c) 2008 the Society for Popular Astronomy The Society for Popular Astronomy has been helping beginners to amateur astronomy -- and more experienced observers -- for more than 50 years. If you are not a member then you may be missing something. Membership rates are extremely reasonable, starting at just £16 a year in the UK. You will receive our bright quarterly magazine Popular Astronomy, regular printed News Circulars, help and advice in pursuing your hobby, the chance to hear top astronomers at our regular meetings, and other benefits. 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