*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 269 2009 June 28 ==================================================== 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/ JUNE 15-16 FIREBALL By Alastair McBeath, SPA Meteor Section Director Much interest was generated just after mid-June by media reports of impressive "meteors" or perhaps an equally imposing "meteor shower" seen from parts of southern England, and apparently reported to coastguards as possible distress flares out over the Channel. As so often with similar media stories over the years, attempting to track down the reality has been difficult, time-consuming, and largely fruitless. At present, just one definite fireball sighting has reached the Section from that night, made from Guernsey, from where the object was seen in the western sky at around 20:30 UT. Confirming colloquial second- or third-hand reports that suggested more than one meteoric object was spotted that evening from other places, has proven impossible to date. It may be that more than one event was involved, but as the Guernsey sighting was made less than half an hour after sunset, that object must have been impressively brilliant to be seen in the strong twilight at all, which alone may account for the excitement generated. Any actual observations of meteors or fireballs (meteors of magnitude -3 or brighter) from June 15/16 - or indeed any other nights - would be most welcome. Information on what details to report from such a sighting (including an e-mail report form) is given on the "Making and Reporting Fireball Observations" page of the SPA website, at: http://snipurl.com/kzlh7 . Those interested in reading more about the claimed event(s) of June 15-16, and the subsequent comments, should see the topic at http://snipurl.com/kzlir on the SPA's General Chat Forum. VERTICAL STRUCTURES IN SATURN'S RINGS SSI In images that are possible only because Saturn is near its equinox, the Cassini spacecraft has observed in the planet's otherwise flat rings vertical structures that are attributable to the gravitational effects of a small nearby moon. The search for ring material extending well above and below the ring plane has been a major goal of the imaging team during Cassini's 'Equinox Mission', the 2-year period around the equinox -- the moment when the Sun is directly over the planet's equator. That geometry, which occurs every half-Saturn-year, or about 15 Earth years, lowers the Sun's angle to the ring plane and makes out-of-plane structures easy to detect by the long shadows that they cast across the rings' broad expanse. In recent weeks, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons, but also the shadows of newly revealed vertical structures in the rings themselves. The observations have lent support to an analysis that indicates how small moons in very narrow gaps can have considerable and complex effects on the edges of their gaps, and that such moons may be smaller than previously believed. The 8-km moon Daphnis orbits within the 42-km-wide Keeler Gap in Saturn's outer A ring, and its gravitational pull perturbs the orbits of the particles forming the gap's edges. The slight eccentricity (the elliptical deviation from a circular path) of Daphnis' orbit can bring it close to the gap edges. There, its gravity causes larger effects on ring particles than when it is farther away. Previous Cassini images have shown that, as a consequence, the moon's effects can be time-variable and lead to waves caused by Daphnis to change in shape with time and with distance from the moon. However, the new analysis also illustrates that when such a moon has an orbit inclined to the ring plane, as Daphnis' is, the time-variable edge waves also have a vertical component to them. That result is supported by new images that show the shadows of the vertical waves created by Daphnis cast onto the nearby ring. The lengths of the shadows indicate wave heights as large as 1.6 km above the ring plane, twice as high as previously known vertical ring structures. The main rings are only about 10 metres thick. PLANET-FORMING DISC ORBITING TWIN STARS AAS A sequence of images collected by a radio telescope in Hawaii clearly reveals the presence of a rotating molecular disc orbiting the young binary-star system V4046 Sagittarii. It has been suggested that the images provide a snapshot of the process of formation of giant planets, comets, and Pluto-like bodies. The results also indicate that such objects may form just as easily around double stars as around single stars like our Sun. The disc orbiting V4046 Sagittarii binary system extends from the approximate radius of Neptune's orbit out to about ten times that radius. The observers believe that V4046 Sagittarii is one of the clearest examples yet discovered of a Keplerian, planet-forming disc orbiting a young star system. The particular system consists of a pair of roughly solar-mass stars that are approximately 12 million years old and are separated by 5 solar diameters. It seems that, at least for some stars, formation of Jovian-mass planets may continue well after the few million years which astronomers have deduced is characteristic of the formation time for most such planets. RARE MAGNETAR DISCOVERED NASA The Swift satellite has reported multiple blasts of radiation from a rare object known as a soft gamma repeater, or SGR. The object, designated SGR 0501+4516, was the first of its type discovered for a decade and is only the fifth confirmed SGR. Astronomers think that the eruptions of SGRs arise from very highly magnetized objects -- magnetars. Magnetars are neutron stars -- the crushed cores of exploded stars -- that, for reasons not yet known, possess ultra- strong magnetic fields, as much as 10*14 times stronger than the Earth's. A magnetar half as far away as the Moon would wipe the magnetic strips off every credit card on the planet. [Silly remark! - of course, if a star were as close as that, magnetar or not, substantial effects could be expected. If the Sun were at that distance, for example, it would do more than just interfere with the magnetic strips on credit cards. -- ED.] Magnetars allow us to study extreme conditions that cannot be reproduced on Earth. Both SGRs and a related group of high-energy neutron stars, called anomalous X-ray pulsars, are thought to be magnetars. But, all told, only 15 examples are known. SGR 0501+4516, estimated to lie about 15,000 light-years away, was discovered only because its outburst gave it away. Astronomers think that an unstable configuration of the star's magnetic field triggers the eruptions. Once the magnetic field resumes a more stable configuration, the activity ceases and the star returns to quiet and dim emission. Twelve hours after Swift pinpointed SGR 0501+4516, XMM-Newton began the most detailed study of a fading magnetar outburst ever attempted. The object underwent hundreds of small bursts over a period of more than four months. Only five days after the initial eruption, INTEGRAL detected X-rays that were beyond the energy range XMM-Newton can see. That was the first time that such transient high-energy X-ray emission has been detected during an SGR's outburst phase; it disappeared again within ten days of the outburst. FIRST EXO-PLANET FOUND IN ANOTHER GALAXY? Discovery Space Only 20 years ago, astronomers were arguing over whether a colleague had discovered the first exo-planet. Researchers have now found more than 300 exo-planets in our Milky Way galaxy, and the new topic of discussion is whether a group of astronomers has detected the first extragalactic planet, in the Andromeda galaxy. A new study to be published in the Monthly Notices of the Royal Astronomical Society explains that it should be possible to identify extragalactic planets with the technique of gravitational micro-lensing, in which a distant source star is briefly magnified by the gravity of an object passing in front of it. That technique has already found several planets in our galaxy, out to distances of thousands of light-years. Extending the method from thousands to millions of light-years should be possible. In fact, it may have already been accomplished. A team of astronomers first conducted a simulation of micro-lensing events in the Andromeda galaxy, which is more than 2 million light-years away. Once they had determined the clues that a planet in Andromeda would show, they looked at a survey, completed in 2004, that showed an unusual light-curve. That event, the group says, matches its theory and can be attributed to a mass about six times that of Jupiter. That suggests either a planet, or a small companion star such as a brown dwarf. Unfortunately, the astronomers cannot go back to check the result from 2004, because micro-lensing events are unpredictable and brief, lasting a few days at most. But the researchers hope to look for stronger evidence of other extragalactic planets. Rather than looking for the transient brightening of distant stars, they will have to look for transient brightenings of individual pixels in the images. A 4-m telescope, continually observing Andromeda for nine months, might pick out one or two exo-planets, simply by analyzing the pixels in the galactic image. [But nine months on a large telescope could make a much more significant contribution to astronomy by being deployed more productively. - ED] 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. 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. The best news is that you can join online right now with a credit card or debit card at our lively website: http://www.popastro.com/ Astronomica is sponsoring the SPA Electronic News Bulletin. 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