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*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 320 2011 November 6 ==================================================== Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is one of Britain's liveliest astronomical societies, 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/ SOLAR ACTIVITY By Richard Bailey, SPA Solar Section Director One of the largest active regions in years, AR 1339, has come into view around the east limb of the Sun, and will change shape over the coming days. It could be a source of flares, as well as filaments and bright plaging. The main sunspot is Earth-sized. It can be viewed by projecting an image of it with a telescope or binoculars onto a shaded white screen, of with specialist solar-filter systems. To see any flares, filaments and plaging, H-alpha filter systems will be needed. A picture of the sunspot can be seen on the Solar link from the SPA website, under News. No attempt must be made to see it by looking directly at the Sun, as permanent eye damage could result. COMET SECTION NEWS By Jonathan Shanklin, Comet Section Director The remains of comet 2010 X1 (Elenin) have been recovered after perihelion by a Spanish observer, working at a remote mountain location in the Cantabrian Mountains. The comet was probably a small object as it had a faint absolute magnitude, and as it approached perihelion it was seen to become more diffuse and fade. In October, over a month after perihelion, Juan Gonzalez detected a cloud of material in the expected location, though his observations were doubted by many Internet 'experts'. They believed that it had completely disintegrated, and when no object could be detected by deep imaging, they poured scorn on the visual observation. They should have remembered history. Similar scorn was heaped on George Alcock when he drew intricate tail detail, but newer technology showed that his visual observations were correct. The long-exposure photographs of the mid-twentieth century had simply blurred out the structure. In the case of the recent disputed observation, amateur wide-field CCD imaging was able (after a few days) to provide the proof that the visual observation was correct. A superb image taken remotely by Rolando Ligustri showed a diffuse cloud of material representing the disintegrated comet. The lesson is that visual observation still has a part to play in scientific discovery. There is a comet that is well placed for observation if you want to see what one looks like. From light-polluted city skies comet 2009 P1 (Garradd) is not easy in binoculars, but in darker rural skies you get a more impressive view. Observations so far show it to have a small, moderately condensed coma about 4 or 5 minutes of arc in diameter, but from my urban location I have not been able to see anything of a tail. Its brightness has not changed much over the last month, as its decreasing distance from the Sun is balanced by its increasing distance from us. The comet will reach perihelion at 1.6 AU just before Christmas, but it is then 2 AU from the Earth. It should be around 7th magnitude, much as it is at the moment. In the new year it will be receding from the Sun, but our distance from it is decreasing, and the comet could become a little brighter. The comet is nearly stationary in southern Hercules in November, but then accelerates northwards, though it is still in Hercules at the end of the year. http://www.ast.cam.ac.uk/~jds/ PLANETS By Andrew Robertson, SPA Planetary Section Director MERCURY reaches eastern elongation on the 14th (23°) but being at only 4° altitude at sunset is effectively unobservable from the UK. VENUS is only slightly better placed, being at 6° altitude at sunset on the 14th, but as it is magnitude -3.9 (compared to Mercury's -0.2) there is a good chance of locating it towards the end of the month just after sunset in the SSW when it will be 8° altitude, provided you have a clear sky and horizon. MARS is an early-morning object. By mid-month at the end of astronomical dark (0515 UT) it is at 47° altitude in the SSE shining at magnitude 1.0 in Leo, near to Regulus which being a blue-white star of magnitude 1.4 will make a pleasant pairing. JUPITER is still king of the planets, having just passed opposition on October 29 and shining at magnitude -2.8. It is observable most of the night. Displaying a diameter of 49" it shows a wealth of detail even in a small telescope, and I have been receiving lots of images and sketches from SPA members. Any reports of observations would be most welcome via: http://popastro.com/planet/contact/ You can see a selection of members' images/sketches at: http://snipurl.com/12a79y ASTEROID 2005 YU55 TO APPROACH THE EARTH ON 2011 NOVEMBER 8 NASA Near-Earth asteroid 2005 YU55 will pass within 0.85 lunar distances of the Earth on November 8. The close approach of this 400-metre C-type asteroid presents an excellent opportunity for optical, near- infrared and radar observations. On November 8 and 9 the object will reach visual magnitude 11 and should be easily visible in modest telescopes. The closest approach to the Earth and the Moon will be respectively 0.00217 AU and 0.00160 AU on November 8 at 23:28 and November 9 at 07:13 UT. Discovered on 2005 December 28 by the Spacewatch Program, the object has been previously observed with the Arecibo radar in 2010 and shown to be a very dark, nearly spherical object 400 metres in diameter. As well as aiding the interpretation of the radar observations, visual and near-infrared observations could define the object's rotational characteristics and provide constraints on the nature of the object's surface roughness and mineral composition. Since the asteroid will approach the Earth from the Sunward direction, it will be a daylight object until the time of closest approach. Although classified as a potentially hazardous object, 2005 YU55 poses no threat of an Earth collision over at least the next 100 years. However, this will be the closest approach to date by an object of such a large size that we know about in advance, and (as far as is known) such an event will not happen again until 2028 when asteroid (153814) 2001 WN5 will pass to within 0.6 lunar distances. ERIS IS PLUTO'S TWIN ESO Eris is one of the largest trans-Neptunian 'Kuiper-Belt' objects in the outer Solar System; it was discovered in 2005, and its discovery was one of the factors that led to the adoption by the IAU of a new class of objects called dwarf planets and the re-classification of Pluto from planet to dwarf planet in 2006. Eris is currently three times further from the Sun than Pluto. In 2010 November, it occulted a faint background star; such occurrences are rare and difficult to observe, as Eris is so distant and its angular diameter is so small. Occultations provide the most accurate, and often the only, way to measure the shape and size of a distant Solar-System body. Observations were attempted from 26 locations around the globe, including several telescopes at amateur observatories, on the predicted path of the shadow, but only at two sites, both in Chile, at one of which there were two telescopes, was an actual occultation observed. The combined observations from the two Chilean sites are consonant with a model of Eris that is close to spherical. While earlier observations by other methods suggested that Eris was probably about 25% larger than Pluto, with an estimated diameter of 3000 km, the new study indicates that the two objects are pretty well the same size. Eris's newly determined diameter stands at 2326 km, with an accuracy assessed at 12 km -- but that is valid only on the assumption that the object is a sphere. Pluto has a diameter estimated to be between 2300 and 2400 km. Pluto's diameter is harder to measure because of the presence of an atmosphere, albeit very tenuous, which creates ambiguities in the understanding of occultation light-curves. The motion of Eris's satellite Dysnomia enables the mass of Eris to be determined; it is 27% greater than that of Pluto. Together, its mass and diameter give its density as 2.52 times that of water, implying that Eris is probably a rocky body covered in a rather thin mantle of ice. The surface of Eris appears to be extremely reflective, reflecting 96% of the light that falls on it (a visible albedo of 0.96 -- brighter even than fresh snow), making Eris one of the most reflective objects in the Solar System, along with Saturn's icy moon Enceladus. The bright surface of Eris is most likely composed of a nitrogen-rich ice mixed with frozen methane, whose presence is suggested by the spectrum, coating the surface in a thin and very reflective icy layer less than 1 mm thick. The layer of ice could result from a nitrogen/methane atmosphere having condensed as frost onto the surface as Eris moved away from the Sun in its elongated orbit into an increasingly cold environment. The temperature of the surface of Eris facing the Sun is estimated to be -238 C at most, and even lower on the night side. The ice could turn back to gas as Eris approaches its closest point to the Sun. COMET STORM IN A NEARBY STAR SYSTEM NASA Astronomers using the Spitzer space telescope believe that they see evidence of an ongoing 'Late Heavy Bombardment' in the 'nearby' southern-hemisphere star system Eta Corvi, occurring at about the same stage of formation of a planetary system as in our Solar System. The Eta Corvi system is approximately one billion years old, which researchers think is about the right age for such a storm. Some scientists think that, about 4 billion years ago, about 600 million years after the Solar System formed, the Kuiper Belt was disturbed by a migration of Jupiter and Saturn, and that the shift in the Solar System's gravitational balance scattered the icy bodies in the Kuiper Belt, ejecting the vast majority into interstellar space and producing a lot of dust in the belt. Some Kuiper-Belt objects, however, were set on inward paths that crossed the orbits of the Earth and other rocky planets. The resulting bombardment of comets lasted until 3.8 billion years ago. The barrage scarred our Moon and produced large amounts of dust. Spitzer has observed around Eta Corvi a band of dust whose spectrum resembles that of the Almahata Sitta meteorite, which fell to Earth in fragments across Sudan in 2008. It is tempting to imagine that the Eta Corvi dust band represents the remnants of an obliterated giant comet, which might have been destroyed by a collision with a planet or some other large body. The dust is located close enough to Eta Corvi that Earth-like planets could exist in the collision zone. A second, more massive ring of colder dust located further out in the Eta Corvi system could be interpreted as a reservoir of cometary bodies. That ring, discovered in 2005, matches the size of the region in the Solar System known as the Kuiper Belt, where icy and rocky left-overs from planet-formation linger. The comets of Eta Corvi, and the Almahata Sitta meteorite, may have each originated in the Kuiper Belts of their respective star systems. BLUE STRAGGLERS IN NGC 188 Northwestern University A consortium of astronomers led from Wyoming has published a study of the old open star cluster NGC 188, which is to be found in Cepheus only 5° from the celestial North Pole. The cluster has around 3,000 stars, all about the same age. In the ordinary course of their evolution, stars burn out, starting from the brightest and most massive ones which burn up their hydrogen much more quickly than those of modest mass. In most cases they finish up by ejecting much of their mass, leaving behind the compact stellar core as a white dwarf. In NGC 188, as in many other clusters, we see a few stars that seem anomalously young, blue and bright, ones that according to the age of the cluster ought to have burnt up and become white dwarfs by now. They are known as 'blue stragglers', and are unusually abundant in NGC 188, which includes 21 of them. It was recognised in the 1960s by W. H. (later Sir William) McCrea that blue stragglers arise from binary-star systems in which the less-massive star collects the expelled envelope of its companion in the final stages of the latter's evolution, and thereby becomes an object that is more massive -- and accordingly burns brighter and bluer -- than any of the stars that are evolving normally as single objects in the cluster. The stripped core of the formerly more-massive star remains as a white dwarf, still in orbit with the rejuvenated blue straggler. The orbital periods are typically of the order of 1000 days. The white-dwarf components of the binaries are not actually detectable directly, being very faint, but their existence is manifested by the orbital motion of their blue- straggler companions. Much of the NGC 188 data set was collected during the last decade by the 3.5-m WIYN Telescope on Kitt Peak in Arizona, but a considerable part was supplied from the Dominion Astrophysical Observatory in Victoria, B.C., and a contribution was subscribed by the moderator of these Bulletins from observations that he made in collaboration with J. E. Gunn with their own radial-velocity spectrometer on the Palomar 200-inch reflector in the 1970s. ANCIENT SUPERNOVA MYSTERY SOLVED NASA In 185 AD Chinese astronomers noted a "guest star" that appeared in the sky and stayed for about 8 months. By the 1960s, scientists had recognized that the object was the first documented supernova. Later, they pinpointed its remnant, called RCW 86, located about 8,000 light-years away. The spherical remains, which cover an area of sky larger than the Full Moon (and can be viewed online at http://go.nasa.gov/pnv6Oy ) are larger than expected. New infrared observations made with Spitzer space telescope and other instruments indicate that the event was a 'Type Ia' supernova, created by the relatively peaceful death of a star like our Sun, which then shrank to become a white dwarf. The white dwarf is thought to have blown up later as a supernova after siphoning matter from a nearby star. The observations also show for the first time that a white dwarf can create a cavity around it before blowing up in a Type Ia event. A cavity would explain why the remains of RCW 86 are so big. When the explosion occurred, the ejected material would have travelled unimpeded by gas and dust and spread out quickly. VISTA FINDS NEW GLOBULAR CLUSTERS ESO Two previously unknown globular clusters were found in new images from ESO's VISTA survey telescope, adding to the total of 158 known globular clusters in our Milky Way. The two faint clusters are known as VVV CL001 and VVV CL002. This small and faint grouping may also be the globular clusters that are the closest known to the centre of the Milky Way. As well as globular clusters, VISTA is finding many open, or 'galactic'. clusters, which generally contain fewer, younger, stars than globular clusters and are far more common. Another newly announced cluster, VVV CL003, seems to be an open cluster that lies in the direction of the Galactic centre, but much further away, about 15000 light-years beyond the centre. It is the first such cluster to be discovered on the far side of the Milky Way. The newly found clusters are so faint that it is no wonder that they have remained un-discovered until now. Because of the absorption of visible starlight by interstellar dust, such objects can be seen only in infrared light. HOW MILKY WAY KILLED OFF SATELLITE GALAXIES RAS Researchers have noticed for the first time the existence of a new signature of the birth of the first stars in our Galaxy. More than 12 billion years ago, the intense ultraviolet light from those stars dispersed the gas of our Galaxy's nearest companions, virtually putting a halt to their ability to form stars and consigning them to a dim future. That explains why some galaxies were killed off, while stars continued to form in more distant objects. The first stars of the Universe appeared about 150 million years after the Big Bang. Back then, the hydrogen and helium gas filling the Universe was cold enough for its atoms to be electrically neutral. As the ultraviolet light of the first stars propagated through the gas, it broke apart the proton--electron pairs that make up hydrogen atoms, returning them to the so-called plasma state in which they existed in the first moments of the Universe. That process, known as re-ionization, also resulted in significant heating, which had dramatic consequences -- the gas became so hot that it escaped the weak gravity of the galaxies of lowest mass, thereby depriving them of the material needed to form stars. The process appears to explain the small number and large ages of the stars seen in the faintest dwarf-galaxy satellites of the Milky Way, and why galaxies like the Milky Way have so few satellites around them. The model appears to match observations of our Galaxy and its neighbourhood and suggests that the first stars of our Galaxy played a major role in the photo-evaporation of the satellite galaxies' gas. It is not large nearby galaxies but our own that caused the demise of its tiny neighbours, evaporating them through its intense radiation. COMPLEX CARBON COMPOUNDS EXIST THROUGHOUT THE UNIVERSE University of Hong Kong Astronomers at the University of Hong Kong have shown that a substance commonly found throughout the Universe contains a mixture of component molecules having many carbon atoms in both 'aromatic' (benzene-ring) and 'aliphatic' (chain-like) arrangements. The compounds are so complex that their chemical structures resemble those in coal and petroleum. Since coal and oil are remnants of ancient life, such matter was thought to arise only from living organisms, but the team's discovery suggests that complex carbon compounds can be synthesized in space even in the absence of life forms. The researchers investigated a set of infrared emissions detected in stars, interstellar space, and galaxies -- spectral signatures known as 'unidentified infrared emission features'. The features have been supposed to come from simple molecules made of carbon and hydrogen atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From observations taken by the Infrared Space Observatory and Spitzer, the observers show that the spectra cannot be explained by PAH molecules but must arise from chemical structures that are much more complex. >From spectra of novae, they show that stars can make such complex compounds on extremely short time scales (weeks). Not only are stars producing such matter, but they are also ejecting it into interstellar space in the form of what astronomers call dust. The work supports an earlier idea that old stars can act as molecular factories. Interestingly, the compounds in star dust are somewhat similar to some found in meteorites, so they must have been present in the early Solar System, of which many meteorites are thought to be relics. Bulletin compiled by Clive Down and moderated by Professor Roger Griffin (c) 2011 the Society for Popular Astronomy