*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 267 2009 May 31 ==================================================== 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/ Astronomica are sponsoring the SPA Electronic News Bulletin. NOCTILUCENT CLOUDS By Ian Brantingham, SPA Aurora Section Director The Noctilucent cloud (NLC) season has begun, with observers, including myself, catching a glimpse of a small patch at 2am on May 29. Information on how, when, and where to observe NLCs can be found at http://snipurl.com/j3hre LYRIDS 2009 By Alastair McBeath, SPA Meteor Section Director Further to the preliminary Lyrid news last time, more data has arrived since, primarily visual and radio, and a more detailed examination of what the shower did this year has been possible. An especially valuable contribution came from members of the North American Meteor Network, NAMN ( http://www.namnmeteors.org ), whose visual observers during the Lyrids were not merely located in North America. Preliminary results from some were provided within days of the event by Rich Taibi (who was unluckily clouded-out for the shower in Maryland, USA), and a full rate summary for all was received more recently from the Network's leader and driving-force, Mark Davis. Reports were available for analysis from every night between April 20-21 to 23-24 inclusive. The outlying results indicated the low activity typically seen from most main showers away from their maxima, but of course the essential night was April 21-22. Two main sets of visual data were to-hand from then, one collected from Europe covering the 23h-03h UT interval, the other from North America, covering the 06h-11h UT period. Although there were too few complete magnitude datasets for certainty, mean magnitudes corrected to a perfectly transparent sky, based on 77 Lyrids and 63 sporadics, were respectively +2.0 and +3.0. These values are about what we would ordinarily expect. Drawing on that assumption suggested Lyrid Zenithal Hourly Rates (ZHRs) were ~11 +/- 3 or higher during the whole of both intervals. They still seemed to have been ~10 +/- 4 even by 06h-08h UT on April 22-23, albeit this was based on just one observer's data. Peaks on April 21-22 seemed plausible around 01h-02h UT (ZHR ~14 +/- 3) and 07h-09h UT (~19 +/- 6 from ~07h-08h, ~14 +/- 2 from ~08h-09h). The International Meteor Organization's (IMO's) "live" data, available on their website at http://www.imo.net/live/lyrids2009/ , roughly concurred, having settled into a pattern for April 22 showing ZHRs of ~14 around 01:40 UT, and ~17 around 08:25 UT. There were however large gaps between datapoints in the IMO results. For example, the 08:25 point fell between one at 03:14 and the next at 12:40 UT. Some caution needs to be exercised with all these numerical values anyway, as the ZHR numbers were relatively small (so a change of two or three could seem to give one or another undue emphasis), and the data samples too were not large enough for real certainty. They do provide the most accurate overview available though, and should be taken as a reasonable guide to what probably happened. An examination of the Radio Meteor Observation Bulletin 189 results for April 2009 (RMOB, kindly provided as ever by Editor Chris Steyaert - see http://www.rmob.org ) indicated better radio-meteor activity was present in the one-hour data-collection bins for April 21-22 beginning at 01h, 05h and especially 07h and 08h UT, which latter period gave the stronger response and was seen in both the European and North American results. Unfortunately, no Japanese data were available, creating a problematic gap in the global coverage. In addition, during all these intervals, the radio-meteor recording geometry was relatively good from one or both continents where observations were reported, which may be misleading. Even so, advancing with a degree of caution once more, it is intriguing there should have been such an apparently close correlation between the visual and radio results for Lyrid peaks within the 01h-02h and 07h-09h UT intervals, both in terms of the timings and the relative peak strengths. It is regrettable there was no visual data to cross-refer with the possible 05h UT radio peak, which might have given further confidence in the results. The complete list of SPA-contributing observers was as follows, where "R" means radio observations were provided (via RMOB 189), "V" visual, and "Vi" video: Salvador Aguirre (Mexico; NAMN; V), Enric Algeciras (Spain; RMOB; R), Orlando Benitez (Canary Islands; RMOB; R), Mike Boschat (Nova Scotia, Canada; RMOB; R), Jeff Brower (British Columbia, Canada; RMOB; R + Vi), Willy Camps (Belgium; RMOB; R), Johan Coussens (Belgium; RMOB; R), Tibor Csorgei (Slovakia; NAMN; V), Mark Davis (South Carolina, USA; NAMN; V), Gaspard De Wilde (Belgium; RMOB; R), David Entwistle (England; RMOB; R + V), Robert Hays (Indiana, USA; NAMN; V), Ken Hodonsky (Illinois, USA; NAMN; V), Javor Kac (Slovenia; NAMN; V), Robert Lunsford (California, USA; NAMN; V), Paul Martsching (Iowa, USA; NAMN; V), Alastair McBeath (England; V), Koen Miskotte (Netherlands; NAMN; V), David Oesper (Wisconsin, USA; NAMN; V), Mike Otte (Illinois, USA; RMOB; R), Andy Smith (England; RMOB; R), "SNOW_JOKE" (England; V), Chris Steyaert (Belgium; RMOB; R), Enrico Stomeo (Italy; Vi), Wesley Stone (Oregon, USA; NAMN; V), Dave Swan (England; RMOB; R), David Swann (Texas, USA; NAMN; V), Felix Verbelen (Belgium; RMOB; R), John Wardle (England; RMOB; R). Very many thanks go to everyone named in this report, for providing results or forwarding data from others, and those who provided helpful additional comments. Any belated Lyrids observations would still be most welcome! MAY 11-12 FIREBALL By Alastair McBeath, SPA Meteor Section Director Among various other fireball sightings since the previous ENB (see our "Recent Fireball Sightings" webpage at http://snipurl.com/j2te2 for information), a spectacular magnitude -9 event around 21:35 UT on May 11-12 stood out. It was reported to the SPA from a dozen places scattered across England, Northern Ireland, Scotland and Wales. However, few of the lucky witnesses were able to give enough detail to allow an accurate trajectory for the meteor to be estimated. It may have flown on a very rough south to north track from above eastern England (maybe somewhere over East Anglia/Cambridgeshire) to a point above the North Sea possibly off the Lincolnshire to North Yorkshire coasts, but this is all most uncertain, and the end may even have been over land near those same coastal districts. Half the witnesses reported the fireball was distinctly green, but a few others noted orange, blue or red was present in it instead. Those people who saw most or all the flight indicated the object remained visible for up to three or four seconds. Four early reports were given on the BBC Scottish News website, at http://snipurl.com/j2tfv , but the suggestion there that the fireball may have originated from the Eta Aquarid meteor shower was quite wrong. Most bright fireballs like this belong to no known shower in general, and linking the event by date to a shower with no supporting evidence is a very common misconception. The most critical problem in making such an association in this case is that the Eta Aquarid radiant was still well below the horizon at 21:35 UT, since it rises only after the start of morning twilight even from southern Britain during May. Anyone else who saw this fireball or any others (a fireball is any meteor that reaches or exceeds magnitude -3) from the UK or nearby, is invited to send in a complete report to the SPA Meteor Section as soon as possible. Please see the "Making and Reporting Fireball Observations" webpage, at: http://snipurl.com/j2tl7 , for what to send and a report form. METEOR SECTION WEBPAGES UPGRADE - LATEST NEWS By Alastair McBeath, SPA Meteor Section Director Work has continued with improvements to the SPA's Meteor webpages during IYA2009, since the first notice about them was circulated in ENB 261 (see http://snipurl.com/j2thq ). The latest set of new pages has been going online since about mid May, and is now complete except for a few minor adjustments. They can be accessed from the "Meteor Reports from 1998-2008" page, itself linked from the Meteor homepage at http://snipurl.com/j2tiz , and provide direct connections to many of the meteoric topics archived online in the ENBs and on the SPA Forums. As well as these links, a set of annotated, annual fireball lists of sightings reported to the Section, is also now available for all years in this millennium. Look out for further upgraded pages later in the year. OBSERVING THE SUN By Richard Bailey, SPA Solar Section Director Lee MacDonald has written some material on observing the Sun for an educational website known as Sun Trek. That might be useful both for the newcomer to the section and also for those helping to bring astronomy to a wider public. The page can be found at http://snipurl.com/i9he4 . MERCURY IS VERY ACTIVE NASA On 2008 Oct. 6 Messenger flew by Mercury for the second time, taking more than 1,200 pictures of the planet. The fly-by has indicated that the planet's atmosphere and magnetosphere, and its geological past, display greater levels of activity than had been suspected. Mercury's magnetosphere had changed a lot since the first fly-by in 2008 January. The magnetosphere is a region of space around Mercury enveloped by the planet's magnetic field. Gusty solar winds buffeting the global bubble of magnetism can potentially trigger magnetic storms and other space-weather-related phenomena. The part of Mercury's surface that was imaged for the first time in October includes a large impact basin, now called Rembrandt, about 700 km in diameter; it was probably formed about 3.9 billion years ago, near the end of the period of 'heavy bombardment' of the inner Solar System. Half of Mercury's surface was unknown until a little more than a year ago. Spacecraft images have since revealed 90% of the planet's surface at high resolution. About 40% of it is covered by smooth plains. Much of Mercury's crust may have formed through repeated volcanic eruptions in a manner more similar to the crust of Mars than to that of the Moon. A third Mercury fly-by is due to take place on Sept. 29, and the probe is intended to be placed into orbit around Mercury in 2011 March. SATELLITE OF SATURN IAU The International Astronomical Union has declared that the recently discovered 53rd satellite of Saturn, designated S/2008 S 1, has been named Aegaeon. PULSAR MISSING LINK NRAO Astronomers have discovered a double-star system that represents a 'missing link' stage in what they believe to be the birth process of the most rapidly spinning stars -- millisecond pulsars. Pulsars are super-dense neutron stars, the remnants left after massive stars have exploded as supernovae. Their powerful magnetic fields generate lighthouse-like beams of light and radio waves that sweep round as the star rotates. Most rotate a few to tens of times a second, slowing down over thousands of years. However, some rotate hundreds of times a second. Astronomers believe that a companion star dumping material onto the neutron star and spinning it up causes the fast rotation. The material from the companion would form a flat, spinning disc around the neutron star; while that was happening, radio waves characteristic of a pulsar would not be seen. As the amount of matter falling onto the neutron star decreased and stopped, the radio waves could emerge, and the object would be recognized as a pulsar. That sequence of events is apparently what happened with a binary-star system containing a millisecond pulsar called J1023, which was discovered in 2007 and is some 4,000 light-years away. The object had previously been detected by the Very Large Array radio telescope during a large sky survey in 1998, and the Sloan Digital Sky Survey had observed it in visible light in 1999, revealing a Sun-like star. When observed again in 2000, the object had changed dramatically, showing evidence for a rotating disc of material, called an accretion disc, surrounding the neutron star. In 2002 the evidence for the disc had disappeared. Then in 2007 observations with the Green Bank radio telescope showed the object as a millisecond pulsar, spinning 592 times per second. No other millisecond pulsar has ever shown evidence for an accretion disc. Another type of binary-star system, called a low-mass X-ray binary (LMXB), also contains a fast-spinning neutron star and an accretion disc, but does not emit radio waves. Astronomers thought that LMXBs are in the process of being spun up, and will later emit radio waves as pulsars. J1023 appears to be the 'missing link' connecting the two types of systems. It appears the object has changed from looking like an LMXB to looking like a pulsar, as it experienced an episode during which material pulled from the companion star formed an accretion disc around the neutron star. Later, that mass transfer stopped, the disc disappeared, and the pulsar emerged. The scientists have studied J1023 in detail with a number of radio telescopes; their results indicate that the neutron star's companion has less than half the Sun's mass, and orbits the neutron star once every 4.75 hours. COSMOLOGY'S 'STANDARD CANDLES' Lawrence Berkeley Lab, Berkeley, California An international group of researchers claims to have found a new technique that estimates the intrinsic brightness of Type Ia supernovae more accurately than before. Such exploding stars are the best 'standard candles' for measuring cosmic distances. Astronomers searching the spectra of 58 Type Ia supernovae found a key spectroscopic ratio. They say that a supernova's distance can be determined to better than 6% uncertainty simply by measuring the ratio of the flux (visible power, or brightness) between two specific regions in the spectrum observed on the same night. The new brightness-ratio correlation appears to hold no matter what the supernova's age or metallicity, its type of host galaxy, or how much it is dimmed by intervening dust. Using classical methods that are based on a supernova's colour and the shape of its light-curve, distances to Type Ia supernovae can be measured with a typical uncertainty of 8-10%. But obtaining a light- curve takes up to 2 months of high-precision observations. The new method provides better accuracy with a single night's full spectrum. The most accurate standardization factor the team found was the ratio between wavelengths 6420 and 4430 Angstroms, in the red and blue parts of the spectrum, respectively. In the analysis, no assumptions are needed about the possible physical significance of the spectral features. GIANT GALAXY MESSIER 87 FINALLY MEASURED ESO At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest cluster of galaxies. It contains many hundreds of galaxies, including giant and massive elliptical galaxies. In particular, it contains the giant elliptical galaxy M87. Astronomers using FLAMES, a spectrograph at the Very Large Telescope in Chile, made measurements of a lot of planetary nebulae in the outskirts of M87 and in the intergalactic space around it within the Virgo Cluster of galaxies. FLAMES can take spectra of many sources, spread over an area of the sky about the size of the Moon, simultaneously. It appears that M87's outer halo has been cut short, with a diameter of about a million light-years, significantly smaller than expected, despite being about three times the extent of the halo surrounding our Milky Way. Beyond that zone only a few intergalactic stars are seen. Numerical models seem to want the halo around M87 to be several times larger than the observations show. Among the speculative explanations of the discrepancy is the possibility that another major galaxy in the cluster, M84, came much closer to M87 and dramatically perturbed it about a billion years ago. COSMIC DISTANCE RECORD BROKEN NASA Gamma-ray bursts are the latest candidates for being the most luminous explosions in the Universe. It is thought that most of them occur when massive stars run out of nuclear fuel. As their cores collapse into black holes or neutron stars, jets of matter punch through the star and blast into space. There, they strike gas previously shed by the star and heat it, generating short-lived afterglows at many wavelengths. Astronomers using the 'Swift' satellite have found a gamma-ray burst from a star that blew up when the Universe was only 630 million years old -- less than 5% of its present age. The event, dubbed GRB 090423, is the most distant cosmic explosion so far recognized. The burst occurred on April 22. Swift quickly pinpointed the explosion, allowing telescopes on the ground to observe it before its afterglow faded away. Astronomers working in Chile and the Canary Islands independently measured its redshift to be 8.2, well in excess of the previous record of 6.7 set by an explosion in 2008 September. KEPLER'S PLANET-HUNT BEGINS JPL The Kepler spacecraft, launched on 2009 March 6, has begun its search for other Earth-like planets. It will spend the next 3.5 years staring at more than 100,000 stars for telltale signs of planets. Kepler could in principle find planets as small as the Earth that orbit Sun-like stars at distances where temperatures are right for water to exist in liquid form. Kepler will hunt for planets by looking for periodic dips in the brightnesses of stars when planets cross in front of them and partially block their light. The first finds are expected to be large gas planets situated close to their stars. SPITZER BEGINS WARM MISSION JPL After more than 5 years of observing cool objects, the Spitzer space telescope has run out of the coolant that chilled its infrared instruments. The telescope will warm up slightly, but two of its infrared detector arrays should still operate. SPECTROGRAPH CAN RECORD ENTIRE SPECTRUM ESO The Very Large Telescope has been equipped with the first of its second-generation instruments, 'X-shooter'. It can record the entire spectrum of an object in one go from the ultraviolet to the near- infrared. The name of the instrument is said to have been chosen (but it must have been done by a crossword-puzzle guru) to stress its capacity to observe a source whose nature and energy distribution are not known in advance of the observation. Until now, some initial information was desirable to indicate which instrument to use for a detailed study. The instrument was installed at the telescope at the end of 2008 and the first observations in its full configuration were made in March and demonstrated that the instrument works efficiently over the full spectral range with satisfactory resolution and quality. X-shooter has already obtained complete spectra of low-metallicity stars, X-ray binaries, distant quasars and galaxies, and the nebulae associated with Eta Carinae and the supernova 1987A, as well as a distant gamma-ray burst that coincidently occurred at the time of the commissioning run. Bulletin compiled by Clive Down (c) 2009 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. 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