*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 255 2008 November 16 ==================================================== 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/ TAURID 'SWARM' RETURN - FIRST NEWS By Alastair McBeath, SPA Meteor Section Director Casual reports reaching the Section have suggested that a few bright Taurids may have been present during late October to early November, along with several UK reports of potential Taurid fireballs in the last days of October, but none of these had sky-tracks well enough established for certainty on their origins. See the list on the SPA's Recent Fireball Sightings webpage at: http://snipurl.com/5jfgl for more information. Although no meteor watch results have arrived from this same period as yet, partly thanks to some unhelpful weather generally over Britain, the International Meteor Organization (IMO) currently has two "live" results' webpages for the Northern and Southern Taurids, at, respectively, http://snipurl.com/5jfjd and http://snipurl.com/5jfk6 . These have indicated little sign that unusual Taurid Zenithal Hourly Rates - ZHRs - were present in late October, though activity from both sources seemed to have been above normal for a few days around November 3-5, and combined ZHRs from both branches could have been up to 20 or so on the latter date. However, caution has to be exercised with these figures, because the values are based on limited datasets so far, so are very preliminary only. If this activity is confirmed, it could support another 'swarm' return having occurred, as hoped-for, though the evidence so far is much less clear-cut than in the relatively fireball-rich return of 2005. ORIONIDS 2008 - PRELIMINARY REPORT By Alastair McBeath, SPA Meteor Section Director The Orionid maximum, due on or around October 20, does indeed seem to have been another interesting one in the sequence that began in 2006, though rates were perhaps not quite so strong at best as suggested in the initial report last time. The "live" IMO results, using just a single, combined datapoint for each full day, have settled into a pattern with highest ZHRs around 35-40 on both October 20 and 21, probably marginally better on October 21. Surrounding this period, ZHRs remained around 25-30 from October 19 to 24 inclusive. Given that previous investigations of the shower had suggested activity at the peak only this year might be 25-30, this was clearly another strong and unusual return. There is still some uncertainty about the exact ZHR values because of the bright Moon, but the extended period of good activity after the maximum was unexpected. Since ENB 254, Assistant Meteor Director David Entwistle and I have examined the radio meteor data (see Radio Meteor Observation Bulletin 183, October 2008, at: http://www.rmob.org , for the reports and details on the contributing observers' systems). David's initial assessment using four datasets including his own, was that, as quite typically, the Orionids failed to give a strong signature in many of the radio results, but that a general peak of some sort was probably present between roughly October 19-23 inclusive. I have just completed a review of all the RMOB results this week, and concur with David's findings for this overall appearance of the shower. However, a degree of finer detail is apparent now. There was a curious difference to the IMO visual results, where a slightly greater number of radio systems favoured a peak on October 22. Activity seemed only marginally lower than this on October 21 and 23 however, but significantly fewer observers found a peak on October 20. Still more intriguingly, several reports suggested a possible additional minor peak on October 25, and close inspection of the data hints that this could have resulted from an increased flux of fainter meteors. There are still too few non-radio datasets in the Section's files to be sure, but the early claims of brighter than normal Orionids, and perhaps increased numbers of fireballs particularly on October 20 and 21, seem not to have been borne out by subsequent results. As noted last time, SPA visual magnitude distributions from October 20-21 and 21-22 seemed quite normal for the shower then. Video observations sent in by Enrico Stomeo in Italy showed nearly identical magnitude distributions for the Orionids on both October 18-19 and 19-20, for example, with no fireballs, and his sporadic magnitudes on both nights were also comparable to one another, suggesting it was not simply different observing conditions at the root. The radio data failed to show any good evidence for unusual numbers of fireballs during the shower either (using longer-duration echo counts), though slightly better rates of these may have been present on October 21. While Britain's ever-unreliable weather thwarted many watchers here, many thanks go to all the following observers for providing some data over the shower, including those on the SPA and UK Weather World Forums, and in October's RMOB. In the list, "V" = visual data were provided, "I" = imaging - photography or video - and "R" = radio: Enric Fraile Algeciras (R; Spain), Orlando Benitez (R; Canary Islands), Mike Boschat (R; Nova Scotia, Canada), Jeff Brower (R; British Columbia, Canada), Willy Camps (R; Belgium), Gaspard De Wilde (R; Belgium), David Entwistle (R; England), "Halo" (V; England), Ed Majden (R; British Columbia, Canada), Martin McKenna (V + I; Northern Ireland), "Melanie" (V; England), Mike Otte (R; Illinois, USA), Jean-Louis Rault (R; France), Robin Scagell (I; England), Andy Smith (R; England), Enrico Stomeo (I; Italy), Dave Swan (R; England), Istvan Tepliczky (R; Hungary), Maarten Vanleenhove (R; Belgium), Felix Verbelen (R; Belgium), John Wardle (R; England) and the Director (V; England). Anyone who still has observations from the Orionids to submit is welcome to do so, preferably as soon as possible, please! SEPTEMBER-OCTOBER METEOR UPDATES By Alastair McBeath, SPA Meteor Section Director The September 25-26, circa 20:55 UT re-entry fireball, mentioned last time as due to part of a Russian Proton rocket launched about half a day earlier, now has a total of 21 sightings in the SPA files, thanks to our French colleague Karl Antier very kindly making available translations of the fifteen observations of it he received. The French data confirmed how unusually slow-moving and long-lasting the event was (in some cases for between 30 seconds to 2 or 3 minutes), and described some heavy fragmentation late in its track. As far as the uncertainties in the visual reports allow, this re-entry seems to have approximately followed its expected atmospheric path, which is reassuring at least! On the SPA's General Chat Forum, at http://snipurl.com/5jfp9 , David Entwistle has provided a link to and some discussion of a fresh image of the very persistent train produced when asteroid 2008 TC3 came down over Sudan on October 7, as predicted shortly before (on which event see also ENB 254). The train itself appears to have lasted for an hour or more, and was imaged after the start of morning twilight from David's calculations. LIVE WEBCAST OF OCCULTATION OF VENUS 2008 DECEMBER 1 By Peter Grego, SPA Lunar Section Director I will be offering a live webcast of the occultation of Venus on the evening of December 1 on my website www.lunarobservers.com The first webcast is from 15:15-45 UT (immersion is at 15:40 UT), the second is from 17:00-17:30 UT (emergence is at 17:13 UT). Location: St Dennis, Cornwall. The instrument will be a 102-mm achromat (Celestron NexStar 102 SLT), imaged afocally with a ToUcam PCVC740K. If the events are clouded out a real-time computer simulation of the occultation will be substituted. THE SUN SHOWS SIGNS OF LIFE NASA After more than two years of few sunspots, and even fewer solar flares, the Sun is finally showing signs of life. During October, five sunspot groups were observed. That may not sound like much, but in a year with record-low numbers of sunspots and long stretches of spotlessness, five is significant and represents a real increase in solar activity. Even more significant is the fact that four of them belonged to Solar Cycle 24, the long-awaited next instalment of the Sun's 11-year solar cycle. Solar Cycle 23 peaked in 2000 and has since decayed to low levels. Meanwhile, the new Cycle 24 has been slow to get started. 2008 is a year of overlap, with both cycles weakly active at the same time. From January to September, the Sun produced a total of 22 sunspot groups, 18 of which belonged to the old Cycle 23. October added five more, but this time four belonged to Cycle 24. At first glance, old- and new-cycle sunspots look the same, but they are not. To tell the difference, solar physicists check two things: a sunspot's heliographic latitude and its magnetic polarity. (1) New-cycle sunspots always appear at high latitude, while old-cycle spots cluster around the sun's equator. (2) The magnetic polarity of new-cycle spots is reversed compared to that of old-cycle spots. Four of October's five sunspot groups satisfied those two criteria for membership in the new cycle. MESSENGER SHOWS MORE OF MERCURY NASA The Messenger spacecraft has passed by Mercury for the second time this year and imaged a further 30% of the previously unseen part of the surface. When combined with data from the first fly-by and from Mariner 10, the latest coverage means that we have now seen about 95% of the planet. Cameras took more than 1,200 pictures of the surface, while the laser altimeter obtained profiles of the topography. The comparison of the new magnetospheric observations with those from the spacecraft's first flyby in January provides new insight into Mercury's internal magnetic field and reveals new features of its magnetosphere. Previous fly-bys by Messenger and Mariner 10 provided data only about Mercury's eastern hemisphere. The most recent fly-by observed the western hemisphere, and showed that the planet's magnetic field is highly symmetrical. The probe's laser altimeter allowed topographic measurements to be correlated with images for the first time at high resolution. A spectrometer observed Mercury's thin atmosphere, known as its exosphere. The instrument searched for emissions from sodium, calcium, magnesium, and hydrogen atoms. Observations of magnesium were the first detection of that element in Mercury's exosphere. Now that Messenger has imaged more than 80% of Mercury, it is clear that, unlike the Moon and Mars, Mercury's surface is more homogeneously ancient and heavily cratered, with large extents of younger volcanic plains lying within and between giant impact basins. ORBITER SHOWS DETAILS OF A WETTER MARS NASA The Mars Reconnaissance Orbiter has observed a new category of hydrated minerals spread across large regions of Mars. Deposits of such minerals indicate where and when water was present. The new observations have identified hydrated silica, commonly known as opal, whose presence suggests that water may have existed as recently as 2 billion years ago, a billion years later than scientists had previously supposed. Until now, spacecraft orbiting Mars had observed only two major groups of hydrated minerals, phyllosilicates and hydrated sulphates. Clay-like phyllosilicates formed more than 3.5 billion years ago where igneous rock came into long-term contact with water. During the next several hundred million years, until approximately 3 billion years ago, hydrated sulphates formed from the evaporation of salty and sometimes acidic water. The newly discovered opaline silicates are the youngest of the three types of hydrated minerals. They formed where liquid water altered materials created by volcanic activity or meteorite impact on the Martian surface. One such location is the large Martian canyon system Valles Marineris. SPITZER STUDIES COMET HOLMES NASA When Comet Holmes unexpectedly erupted in 2007, astronomers around the world turned their telescopes toward the spectacular event. People would naturally like to know why the comet had suddenly exploded, but observations recently reported from the Spitzer space telescope do not answer the question, showing only oddly-behaving streamers in the shell of dust surrounding the nucleus. The Comet Holmes explosion gave us a rare glimpse of material from the inside of a comet nucleus, and the data do not look like anything we typically see in comets. Every six years, Comet Holmes heads inwards towards the Sun from the distance of Jupiter's orbit. Usually it travels without incident, but twice in the last 116 years, in 1892 November and 2007 October, it suffered an explosion as it approached the asteroid belt, and brightened a millionfold overnight. Spitzer observed the comet last November and again in March. Its infrared spectrograph gave indications of the composition of Holmes' solid interior. The November observations showed a lot of fine silicate dust and materials similar to those seen around other comets where grains have been treated violently, as in the Deep Impact mission, which smashed a projectile into Comet Tempel 1. Comet dust is very easily destroyed and it is thought that the fine silicates are produced in violent events by the destruction of larger particles originating inside the comet nucleus. When Spitzer observed the same portion of the comet again in March, the fine-grained silicate dust was gone and only larger particles were present, so there seems to be only a small window of time for studying comet dust after a violent event. Comet Holmes not only has unusual dusty components, but it also does not look like a typical comet. Pictures taken from the ground shortly after the outburst showed streamers in the shell of dust surrounding the comet. Scientists suspect that they were produced after the explosion by fragments escaping the comet's nucleus. In 2007 November the streamers pointed away from the Sun, which agreed with the idea that radiation from the Sun was pushing the fragments straight back. However, when Spitzer imaged the same streamers in March, they were still pointing in the same direction even though the comet had moved and sunlight was arriving from a different direction. EPSILON ERIDANI HAS TWO ASTEROID-LIKE BELTS Harvard-Smithsonian CfA The Spitzer infrared telescope has observed Epsilon Eridani, a star that is younger and slightly smaller and cooler than the Sun and, at a distance of only 10.5 light-years, is the ninth-closest star. The star proves to have three rings of cool material that emit radiation only in the infrared. It is conjectured that the radiation arises from bands of asteroid-like objects. The innermost band is about 3 astronomical units from the star, just like the asteroid belt in the Solar System, and judged by its brightness it contains an amount of material comparable with that in our asteroid belt. The second ring seen in the infrared is at about 20 astronomical units from the star (about the distance of Uranus from the Sun) and appears to hold about 20 times as much material as the first. A third ring, that has been observed previously, extends from about 35 to 100 astronomical units from Epsilon Eridani. A possibly analogous band in the Solar System is called the Kuiper Belt; however, judged from its brightness, Epsilon Eridani's outer ring holds about 100 times more material than ours. The Spitzer data show gaps between the successive rings surrounding Epsilon Eridani. Such gaps might be explained by the presence of planets that constrain the rings gravitationally, just as the moons of Saturn constrain its rings. MARS ROVERS UPDATE New Scientist The arrival of spring in the southern hemisphere of Mars is reviving the two venerable Mars rovers as deepening autumn in the arctic north freezes the Phoenix lander, which failed to wake up on November 2. After hibernating for the winter on the northern edge of a plateau, the 'Spirit' rover moved uphill in October to collect more sunlight. On the other side of the planet, the 'Opportunity' rover, which climbed out of a large crater called Victoria at the end of August, has completed the first month of a 12-kilometre trek towards an even bigger crater called Endeavour. That journey is expected to take more than two years. Designed to last only 90 days, the two rovers have survived for nearly five years. Once it started moving, Spirit was able to climb slopes of up to 30°. However, two weeks of movement has not dislodged the dust that limits the power generated by its solar arrays. Winds have blown dust off Opportunity's solar panels, so they generate more than 25 watts and allow the rover to move faster, but it must navigate carefully across ground that includes soft dunes where it could get stuck. The rover can travel up to 100 metres in an hour, but it can see only 20 to 30 metres ahead. That means that it has to stop regularly to send pictures of the prospect so that controllers can pick out a safe path. Both rovers will have to be parked during an interruption in communications from November 29 to December 15, when the Sun will be between Mars and the Earth. Bulletin compiled by Clive Down (c) 2008 the Society for Popular Astronomy Looking for the perfect Christmas gift for a budding young astronomer? Then how about a gift subscription to the SPA's Young Stargazers' club? For just £10 a year, Young Stargazers receive an A4 file packed with information, from how to choose a telescope or binoculars, to an A-Z of astronomical terms, night-sky observing projects, and a guide to the world's biggest telescopes. 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