*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 259 2009 January 18 ==================================================== 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/ JANUARY 9 UK FIREBALL By Alastair McBeath, SPA Meteor Section Director After a fairly quiet December for fireball sightings, other than near the Geminid and Ursid maxima, IYA2009 has opened with a clutch of non-Quadrantid fireballs for the UK. Most were reported from single locations only (see the SPA's "Recent Fireball Sightings" webpage at http://snipurl.com/a8ber for details). However, one on January 9-10 was more widely-seen, from at least seven places in western England and south Wales (Lancashire to Gwent). It happened within eight minutes of 18:47 UT, and was around magnitude -5 to -8, according to the more detailed observations. Its possible atmospheric trajectory has not been firmly-established, but a best estimate from the reports suggests it may have been moving roughly NE to SW, starting somewhere high above northwest or central-western Wales, heading out over Cardigan Bay towards St George's Channel. More accurate positional data on where the fireball started and ended in the sky from different locations would be needed to improve this. Most witnesses described the meteor as slow-moving, and it was visible for probably 3 to 4 seconds or more. Colours reported have included blue, red, orange and yellow, plus green perhaps in the object's tail. Some of the sighting reports can be found on the Observing Forum, at http://snipurl.com/a8mvd, and among the postings on the UK Weather World's Space Weather Quadrantids topic, at http://snipurl.com/a8myb . Regular ENB readers may recall there was also a bright, UK-seen fireball on January 9-10 in 2008, around 18:55-19:00 UT (see ENB 236, archived at http://snipurl.com/a8n38 ). This seems to be nothing more than a curious coincidence though, and there is no evidence to link the two objects beyond their rough timings. Anyone else who spotted the 2009 January 9 fireball, or any others - meteors of magnitude -3 or brighter - from the British Isles and nearby is welcome to send a full report to the Meteor Section as soon as possible. The minimum details I need from you are: 1) Exactly where you were (name of the nearest town or large village and county if in Britain, or your geographic latitude and longitude if elsewhere in the world); 2) The date and timing of the event; and 3) Where the fireball started and ended in the sky, as accurately as possible, or where the first and last points you could see of the trail were if you didn't see the whole flight. More advice and a fuller set of items to send are outlined on the "Fireball Observing" page of the SPA website, at: http://snipurl.com/a8n8f. QUADRANTIDS 2009 - PRELIMINARY DETAILS By Alastair McBeath, SPA Meteor Section Director A strong, unusually protracted, Quadrantid maximum seems to have happened on January 3, judging by the initial "live" International Meteor Organization's (IMO's) findings, available via the http://www.imo.net homepage. Visual Zenithal Hourly Rates (ZHRs) were around 40-60 for much of the European night of January 2-3, but started rising quickly after 03h UT or so, to be over 100 before 05h. By 09h UT over North America, ZHRs had already crested the usual peak level of ~120, reaching ~130-150 for a time. Rates then continued at or above 120 till about 13:30, possibly with two main peak phases when ZHRs topped-out around 160, centred on ~10:30, and again for more than half an hour to either side of 13:00. Even by nightfall over Europe on January 3-4, ZHRs were still just above 100 (albeit the ZHRs were calculated from results collected elsewhere, because of the very low radiant elevation then from Europe), but dropped rapidly afterwards, to be back below 30 before 01h UT that night. The Quadrantid peak was due around 13h UT on January 3 (see ENB 257, at http://snipurl.com/a8ndh ), so a lot of this excellent activity happened before that was due, as well as almost exactly when it was. Sadly, and rounding-off a remarkably poor spell for UK weather throughout the autumn and early winter, very few people in Britain saw much of the Quadrantids at all, as the comments on the Quadrantids topics on the SPA's Observing Forum (at http://snipurl.com/a8pil ) and on the UK Weather Watch's Space Weather Forum (address above) helped indicate. Quadrantid data of some sort, including casual visual watch comments from these two Forums, has so far reached the SPA from: "@@" (West Midlands), Jeff Brower (British Columbia, Canada; radio & video), Assistant Meteor Director David Entwistle (Lancashire; radio), Rob Hale (Cheshire), Pete Lawrence (West Sussex; imaging - see the SPA Quadrantids topic for links to Pete's images), "markt" (West Midlands), Dave Mitsky (eastern USA), Dave Scanlan (Hampshire), Enrico Stomeo (near Venice, Italy; video), and Rich Taibi (Maryland, USA). Jeff's and David's radio data featured on the SPA Forum too, while Jeff alerted me to a new webpage reporting analyzed radio results in graphical form collected from Japan, with short English notes, at http://snipurl.com/a8pom . Rather like the IMO's "live" visual results, this page needs to be treated with caution, as it is a preliminary set of findings, but it does give some interesting ideas to what may have happened. Jeff's and David's analyzed results were also shown there, albeit uncredited (as the "Canada" and "England" graphs respectively). Enrico's video results, plus the limited UK visual comments and Pete's imaging, all confirmed sharply-rising activity towards the end of the night on January 2-3. Dave Mitsky's and Rich Taibi's visual reports from the eastern USA showed the early part of the good to excellent activity the IMO visual data found, while suggesting Quadrantid magnitudes were fairly ordinary to possibly somewhat fainter than usual. This could have affected the ZHRs, if borne-out by reports from elsewhere, since if many faint meteors were present, the computed ZHRs may have underestimated the true activity. The radio results suggested good shower echo-counts persisted virtually throughout January 3, at best from roughly midday to 18h UT, though the highest radio rates may have peaked a couple of hours after the visual ones (the Japanese webpage has an interesting graph which shows this quite well). The radio details will need confirming once more data is in, however. One other facet of the radio reports, again still unconfirmed, was that Jeff's data and the Japanese observations seemed to show a minor peak around 18h UT on January 3. The IMO's visual data is rather limited over this time unfortunately, and though it has been suggesting a possible short- lived resurgence in activity, perhaps to ZHRs of ~80-90 around 19:30 on January 3, it is not clear yet whether either of these late "peaks" resulted from a genuine activity increase, or if they were simply artefacts of the analyses. Many thanks to all the contributors listed above. All further Quadrantid observations gratefully received! URSID & GEMINID UPDATES By Alastair McBeath, SPA Meteor Section Director The recent publication of Radio Meteor Observation Bulletin 185 for last December (see http://www.rmob.org for the data, the observers, to whom go fulsome thanks, and their equipment), has allowed a more detailed appraisal of radio meteor activity during the Ursid and Geminid showers, to what was discussed in the previous ENB. Fresh findings from the SPA analyses across both shower peak dates follow. During the Ursids, there was an indication of a possible minor radio maximum around 13h-14h UT on December 21, and another at 20h-21h, roughly coincident with the small Ursid peak found in one video dataset as reported last time (this has now been shown by a second detailed video report thanks to Roberto Haver in Italy too). However, the main active phase in the radio data lasted from about 00h-10h UT on December 22, especially consistently from roughly midnight to ~05h. Within that interval, the stronger and better- recorded maxima were between 01h-03h (especially between 01h-02h), 07h-08h, and 09h-10h UT. Activity seemed to be lowest overall during this time around 06h-07h and 08h-09h UT. There was no evidence to support the minor peak near 23h UT on December 21, suggested from the initial video results, but Ursid activity was apparently creating somewhat increased echo-counts from 20h-24h UT on the 21st even so. There was a possible further slight radio peak around 15h UT on December 22, though not later, so no confirmation was practical of the minor radio maximum from ~18h-20h UT then which Jeff Brower found in his initial radio report. In general, these results supported those given in ENB 258, especially for the main maximum period early on December 22, but the strength of the ~09h-10h UT radio maximum was unexpected, as there was no corroborating visual evidence from North America then. In the radio data, this peak seemed similar in strength to the 02h-03h UT activity. Although radio and visual activity cannot be directly compared, it is interesting the 02h-03h UT interval brought visual ZHRs of ~20 +/- 5, and the radio evidence implied the ~09h peak was at least as rich in brighter meteors as either the ~01h or ~07h maxima. Only more data will allow further investigation. The radio Geminid maximum has proven more difficult to define than expected, as suggested last time. Just why this was so is uncertain. With very strong meteor showers, there is sometimes an effect caused by meteors occurring close together in time, so automated radio receivers become saturated with echo counts blurring into one another. This can artificially reduce the total number of echoes recorded below even normal levels. While this may have contributed to the difficulties this time, it seems unlikely to have accounted for all the analysis problems. Overall, most of the operational radio systems favoured a maximum between 22h UT on December 13 and 05h UT on the 14th, but after allowing for the more favourable radio-observing circumstances, no better-defined peak than this could be established, so no confirmation of the very strong visual rates reported especially between 03h-04h UT on December 14 has been possible this way. One particularly curious addition is that a significant number of radio results suggested a weaker peak may have fallen between roughly 22h-02h UT, perhaps persisting till ~06h-07h, on December 12-13. Some datasets even showed better activity during this interval than on December 13-14! Last century, it was established that some mass-sorting of meteoroids had occurred in the Geminid stream, and that telescopically-faint Geminids, similar to what some radio meteor systems detect preferentially, seemed to reach maximum approximately one day ahead of the visual peak. It may be this is what the radio results picked up in 2008. SPACE HAS NEVER BEEN CLOSER NASA-GSFC Observations made by instruments on a US air-force satellite have shown that the boundary between the Earth's upper atmosphere and space has moved to extraordinarily low altitudes. The satellite was designed to study disturbances in the Earth's ionosphere, which is a gaseous envelope of electrically charged particles that surrounds the Earth and is important because radar, radio waves, and signals for global positioning systems can be disrupted by ionospheric disturbances. The satellite's first discovery was, however, that the ionosphere was not where it had been expected to be. The transition between the ionosphere and space was found to be at about 260 miles altitude during the night-time, rising to about 500 miles during the day. Those altitudes were unusually low compared with the more typical values of 400 miles at night and 400 miles by day. COMET IMPACTS MAY HAVE TRIGGERED ANCIENT FAMINE New Scientist It has been proposed that multiple comet impacts around 1500 years ago may have triggered a 'dry fog' that plunged half the world into famine. Historical records tell us that from the beginning of 536 March a fog of dust blanketed the atmosphere for 18 months. During that time, the Sun (it was said) gave no more light than the Moon, global temperatures plummeted and crops failed. The cause has been unknown, but theories have included a great volcanic eruption or an impact from space. Now scientists have found the first, indirect, evidence that multiple impacts caused the haze. They found tiny balls of condensed rock vapour or 'spherules' in debris inside Greenland ice cores dating back to early 536 AD. Though the spherules' chemistry suggests that they did not belong to an impactor, they do point to terrestrial debris ejected into the atmosphere by an impact event. That represents the first actual geological evidence for an impact in 536. The fallout material was laid down over several years, and some layers were particularly densely deposited. That suggests that more than one impactor was involved -- probably comets, which do tend to fragment. Two possible submarine craters whose age ranges fit the global dimming event have been identified -- one is in the Gulf of Carpentaria in Australia, and the other in the North Sea near Norway. Marine micro-fossils found with the impact spherules are consistent with an ocean impact. ASTEROIDS WITH EARTH-LIKE CRUST Carnegie Institution It has sometimes been assumed that the small size of asteroids limited the types of rock that could form in their crusts, but researchers report that two newly discovered meteorites are ancient asteroid fragments consisting of feldspar-rich rock called andesite, previously known only from the Earth. The two light-coloured meteorites were discovered in a region of the Antarctic ice known as the Graves Nunatak ice-field. The unusual thing about them is that they have compositions similar to the Earth's continental crust. Andesite is an igneous rock common on Earth in areas where colliding tectonic plates generate volcanoes, such as those of the Andes. The meteorites contain minerals thought to require large-scale processes such as plate tectonics to concentrate the right chemical ingredients. In view of that, some researchers suggested that the meteorites are fragments of a planet or the Moon, not an asteroid, but analysis of the meteorites' oxygen isotopes ruled out that possibility, and it now seems likely that the formation of andesite crust can occur by processes other than plate tectonics. Several Solar-System objects, including parent bodies of meteorites, planets, moons, and asteroids, have characteristic oxygen-isotope signatures, and just by analyzing the isotopic ratios we can tell if a meteorite came from Mars, from the Moon, or from a particular asteroid. One extensively studied parent is the asteroid 4 Vesta. In the majority of cases the actual location of the parent body is unknown but, even so, a particular group of meteorites may still be assigned to the same parent body on the basis of the isotopic ratios. The ratios in the newly found meteorites are nearly coincident with those of meteorites from 4 Vesta. The meteorites' age, more than 4.5 billion years, suggests that they formed very soon after the birth of the Solar System, making it unlikely that they came from the crust of a differentiated planet. The chemical signature of some rare metals, notably osmium, in the meteorites also points to their origin on an asteroid that was not fully differentiated. The researchers hypothesize that that the asteroid had a diameter somewhat larger than 100 kilometres, which would be sufficient to hold enough heat for the asteroid's rocks to be partially, but not completely, melted. The asteroid would remain undifferentiated, but the melted portions could erupt onto the asteroid's surface to form the andesitic crust. JUPITER-LIKE PLANETS MUST FORM QUICKLY Harvard-Smithsonian Center for Astrophysics Jupiter must have gained mass very quickly when it was forming, since the rest of the material from which it formed probably dispersed in just a few million years, according to a new study of planet formation around young stars. Astronomers examined the 5-million-year-old star cluster NGC 2362 with the Spitzer space telescope, which can detect the signatures of actively forming planets in infrared light. They found that all stars with the mass of the Sun or greater have lost their protoplanetary (planet-forming) discs. Only a few stars less massive than the Sun still retain their discs. Such discs provide the raw material for forming gas giants like Jupiter. Therefore, if gas giants do not form in less than 5 million years they probably won't form at all. Even though nearly all the discs that could form gas-giant planets in NGC 2362 have disappeared, several stars in the cluster have 'debris discs', which indicates that smaller rocky or icy bodies may still be forming. FEW BROWN DWARFS ACCOMPANY STARS Space Telescope Science Institute The Hubble telescope has been surveying the complete sample of stars known to be nearer than 10 parsecs (32.6 light-years). Part of the intention is to discover and characterize 'missing' members of the sample. The sample includes 239 known red dwarf stars (normal stars that are about half the diameter and a fifth ofthe mass of the Sun and with much lower surface temperatures), and there are 12 known brown dwarfs. Only two brown dwarfs were found as companions to normal stars. Since brown-dwarf binaries do exist, the fact that there are very few binaries whose components lie on opposite sides of the hydrogen-burning limit -- the division between normal stars and brown dwarfs -- must be seen as significant, although what the significance actually is remains unknown. DISCS ROUND DEAD STARS MAY BE FROM DEAD ASTEROIDS NASA/JPL Observations made with the Spitzer telescope are interpreted as indicating the existence of the remains of shredded asteroids around six dead white-dwarf stars. Spitzer's infrared spectrograph observed dusty discs around eight white dwarfs and found that the dust contains a glassy silicate mineral similar to olivine and commonly found on Earth. The Spitzer data also suggest that there is no carbon in the rocky debris. The gravitational tides that could be raised by a white dwarf in a rocky body that got too close would be enough to tear that body apart. It is being proposed the asteroid-like bodies have met such a fate within the last million years in the cases of the white dwarfs recently investigated by Spitzer. The amount of material is such that in one case it might have constituted an asteroid 200 km in diameter. So far, the results suggest that the same materials that make up the Earth and our Solar System's other rocky bodies could be common in the Universe. ASTROPHYSICISTS MAP MILKY WAY'S 4 SPIRAL ARMS Iowa State University As the Sun and other stars revolve around the centre of the Milky Way, we cannot see the spiral arms directly, but have to rely on indirect evidence to find them. In visible light, the Milky Way appears as an irregular, densely populated strip of stars. Dark clouds of dust obscure the Galaxy's central region, so it cannot be observed in visible light; if it were not for the obscuring clouds its brightness would be comparable with that of the Moon and be a great hindrance to astronomers. Infrared light, however, can penetrate the dust clouds, so astrophysicists have used satellite-infrared data to model the distribution of molecular gas in the Galaxy and thereby to map the Galaxy's spiral arms. The stars in the Milky Way are thought to be distributed as a disc with a central bulge dominated by a bar-shaped arrangement of stars. Outside the central area, stars are located along spiral arms. In addition to the two main spiral arms in the inner Galaxy, there are thought to be two weaker arms which end about 10,000 light-years from the Galaxy's centre. (The Sun is about 25,000 light-years from the Galactic centre.) One of the weaker arms has been known for a long time, but there has been concern over its large deviation from circular motion, which is now attributed to gravitational effects of the newly identified central bar. The other weak arm, on the far side of the Galaxy, was recently found in gas data. The discovery of that second arm was something of a relief, affirming that the inner Galaxy is indeed quite symmetrical in structure as had been supposed. MILKY WAY SPINS FASTER AND IS MORE MASSIVE THAN WAS THOUGHT NRAO In some regions of prolific star-formation in the Galaxy there are cosmic masers, areas where gas molecules are strengthening naturally- occurring radio emission in the same way as lasers strengthen light beams. By repeatedly measuring maser positions very accurately by radio interferometery using intercontinental baselines, at times when the Earth is at opposite sides of its orbit around the Sun, radio astronomers can measure parallaxes (and thereby distances) for objects at great distances in the Galaxy. Some of such direct distance measurements differ from earlier, indirect measurements, sometimes by as much as a factor of two. The star-forming regions harbouring the cosmic masers define the spiral arms of the Galaxy, so the measurements are helping to improve our understanding of the structure and motions of the Galaxy. They also indicate that the Milky Way is rotating somewhat faster than had been thought previously, such that the circular velocity in the vicinity of the Sun is more like 260 km/s rather than the 200 km/s that has long been accepted. The increase implies that our Galaxy is correspondingly more massive, so it is now seen as being on a par with the Andromeda Nebula. MARS ROVERS HAVE LASTED FIVE YEARS JPL Spirit and Opportunity approach the fifth anniversaries of their landings on Mars. No one expected, when they landed early in 2004, with a three-month nominal service life, that they would still both be operating in 2009, The rovers have made important discoveries about wet and violent environments on ancient Mars and have returned a quarter of a million images, driven more than 21 kilometres, climbed a mountain, descended into craters, struggled with sand traps and ageing hardware, survived dust storms, and relayed a great deal of data via the Mars Odyssey orbiter. JUNE RESTART FOR LHC Web User The Large Hadron Collider, the world's biggest particle accelerator, may be started again by the summer. Soon after it was switched on in September last year, it suffered a catastrophic malfunction whereby super-cold helium leaked into the system. Many of the magnets used to accelerate the particles needed to be repaired as a result, at a cost of around £20m. 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