Report of the
meeting held on
section meeting, hosted by Newbury Astronomical Society,
was held on
The presentations, in PDF format, can be accessed by following the links highlighted in bold below. Other relevant links are also highlighted in regular font.
The Section Director, Roger Dymock, opened the meeting by welcoming the attendees and outlining the day’s program. He noted that Bob Mizon was present with his Campaign for Dark Skies stand and books, surplus to the Section’s requirements, were being offered for sale. Non-members present were encouraged to join the Section. There is no joining fee although membership of the British Astronomical Association is strongly encouraged and joining details could be had from the Association’s stand run by Ann Davies.
row, left to right: Roger Dymock, Andrew Elliot, Richard Miles,
row, left to right: Mark Kidger, Alan Harris,
first speaker was Eamonn Ansbro who
is currently developing a range of telescope facilities at Kingsland
Edgeworth-Kuiper Belt Objects (EKBO’s) orbit beyond Neptune and offer important clues about the formation of our solar system. Far from resembling an accretion disk leftover, the discovery of some EKBOs with inclinations as high as 40 degrees demonstrates that the full latitudinal extent of the EK belt must be large. Ascertaining the true extent of the inclination distribution of Trans-Neptunian Objects (TNO’s) is important for planning TNO surveys. It is vital for determining the total number of TNO’s and the past and present mass contained in the EK belt. It will also provide data that may confirm or alter our understanding of solar system formation.
Past surveys of TNOs are probably a poor representation of the true distribution of EKBO inclinations because most were found in surveys centred on the ecliptic. Such surveys were biased towards finding low inclination objects which spend the majority of their orbit close to the ecliptic.
A 0.9 metre telescope at Kingsland Observatory, County Roscommon, Ireland is carrying out a two year statistical survey by imaging a range of ecliptic latitudes that are equidistant from each other and measuring the density of EKBOs found at each latitude. Imaging sets of fields spaced uniformly North of the ecliptic will also determine the resonance structure imposed on the belt by the gravitational effects of Neptune. At each longitude, fields at several ecliptic latitudes will map the inclination distribution of the belt, testing competing theories for the formation and orbital evolution of the giant planets.
The survey also includes a search for a hypothetical ninth planet beyond the EKB as a follow-up survey of some 'suspected planets'. The follow-up survey this year will attempt to detect whether or not this planet exists based on the targets located by prior research.
Only slightly more than a decade after the discovery of the first asteroid binary, more than 100 of them have been discovered by a variety of techniques. Over the same period of time, the number of asteroid with known rotation properties has more than tripled. This has been largely due to the advent of robotic CCD telescope systems, many of them owned by amateur astronomers. Not only have these observers taken the lead in lightcurve observing, they are now the leading mode of discovery of binary asteroids, through lightcurve observations of eclipses. This explosion in data has gone hand in hand with theoretical work on radiation pressure alteration of asteroid spins (YORP effect) to revolutionize our picture of the physical state and evolution of the small bodies in the solar system.
Survey for Asynchronous Binary Asteroids" is a
collaborative effort between professional and amateur observers, led by Petr
pole/orbit orientations of binaries and look for eclipse events at other geometries than previously observed. Further details, along with a listing of participating observers, can be found at http://www.asu.cas.cz/~asteroid/binastphotsurvey.htm.
An excellent buffet lunch was provided by Ann Davies assisted by Monica Balstone and Colin Stevens.
The afternoon sessions opened with Andrew Elliott, Assistant Director (Occultations), giving an update on the ‘Techniques of Occultation timing’.
The presentation covered the basic techniques of observing, timing, and recording planetary, (+dwarf planetary!), asteroid, and planetary satellite occultations. The "New Order" in equipment and techniques available to the modern well-equipped amateur were then discussed. These included telescopes, 'impersonal' timing and recording equipment, accurate time sources, site coordinates, predictions, reduction software, mobile observing, and collaboration in European and worldwide pro-am networks via the internet.
The next speaker on ‘Aspects of Asteroid Photometry: Observing campaigns’ was BAA President and Assistant Director (Photometry), Dr Richard Miles.
Amateurs equipped with CCD cameras can help push back the scientific frontiers in asteroid research. To do this effectively requires them to unite with others or, at the very least, coordinate their observations with those of others eg: Brain Warner’s Collaborative Asteroid Lightcurve Link (CALL), Raoul Behrend’s CdR-CdL and Petr Pravec’s Binary Asteroid Group. This talk recalled how observing campaigns have developed over the years and set out the various options now open to interested observers. BAA activities were highlighted and future observing campaigns mooted based on the data in the 2007 and 2008 BAA Handbooks.
Before the mid-afternoon break Dr. Mark Kidger, Community Support Scientist to the Herschel Space Observatory, working at the Herschel Science Centre of ESA's Villafranca del Castillo Satellite Tracking Station in Madrid, gave the first of his two talks titled ‘Catalogues for asteroid photometry – facts and myth’
Mark Kidger was the only speaker to include an image of me in their presentations – the lad will go far !!!
The magnitude scale was developed by Ptolemy – a difference of 5 magnitudes being equal to a change in brightness by a factor of 100. Originally 6 orders of magnitude were defined whereas today the range is approximately 55 from the Sun (-26.7) to the faintest objects detected by the Hubble Space Telescope (approximately 29). Amateur astronomers need to be able to calibrate their photometry down to at least magnitude 18 and preferably fainter. Badly calibrated data is useless and misleading if published. The aim should be to quote a magnitude in a known system or one that can be converted to same.
Mark emphasized the Photometrist’s Commandments – be systematic and understand your limitations. The limit to accuracy, no matter how well you calibrate and how good the seeing conditions are is about 3% or 0.03 magnitudes. Even if the error is known to be large it should be quoted. A good signal to noise ratio (SNR) is vital for accurate measurement of magnitude
Since 1990 he has worked with a group of astronomers in Tenerife with the objective of obtaining high precision photometric calibration of stars using Landolt stars as a reference. The Tycho 2 catalogue shows reasonably good correlation with Landolt stars down to magnitude 10. For best results he recommended using Tycho calibration stars with a V magnitude brighter than 9, a small colour index and within 1 degree of the object being imaged. Calibration stars should be imaged frequently, say every 10 minutes or so and imaging should be not lower than 30 degrees altitude. Results should be transformed to the Johnson V scale. Ideally Landolt stars should be used but there may not be many near to the field of interest. In an ideal world one would use reference stars in the same field of view/image as the asteroid/variable object. Unfortunately such stars are not well calibrated. For example the USNO A2 catalogue is accurate to only 0.17 magnitudes in V, 0.20 in B and 0.15 in R.
His second talk, after the break, was ‘The asteroid impact risk reviewed: has it been greatly overestimated ?’
Hollywood has done a good job in bringing the impact hazard to the public notice but the science in the movies often leaves something to be desired. The extinction of the dinosaurs can be linked to the Yucatan impact but the Deccan traps volcanic eruption may also have played a part. Although the impact rate is much lower than it was the danger is still there. 2008 is the centenary of the Tunguska event and it is expected that this will bring the subject to the fore once again. In December 2004 a conference, organized by the International Council of Science and attended by a multi-disciplinary group of 50 scientists was held in the Tenerife Science Museum. Its aim was to discuss all aspects of the asteroid threat. Just 3 weeks after the conference the Asian tsunami struck causing significant loss of life and considerable damage indicating just what an ocean impact might do.
The potential threat is indicated by the 138 asteroids on the JPL Current Impact Risk List of which only 5 have been observed recently. The combined impact probability of all these asteroids gives a 1% chance of an asteroid hitting the Earth in the next century. However 70% of that probability can be assigned to just 2 objects both of which are small and may not penetrate the atmosphere to reach the Earth’s surface.
After describing his observatory Peter explained how he used the Minor Planet Center’s NEO Conformation page (MPC NEOCP) to follow up recent discoveries. He explained that newly discovered asteroids can be difficult to find or lost if they are Very Fast Moving Objects (VFMO’s) or there is a delay in their appearance in the NEOCP. As do many amateurs Peter uses Astrometrica. This enables faint objects to be detected by stacking multiple images and outputs data in the format required by the MPC. His technique for capturing images of VFMO’s is to take many short exposures of a number of fields spanning the predicted position of the object. Timing is all important for accurate astrometry particularly of VFMO’s. Synchronising the PC’s clock using Dimension 4 Freeware is Peter’s preferred method but he noted that GPS receivers are also suitable timekeepers. He closed his presentation by mentioning that distant artificial satellites make good targets for practicing VFMO imaging.
Roger Dymock brought the meeting to a conclusion by thanking the speakers, the attendees and those who had worked hard to make the day a success: Ann Davies, Monika Belstone and Colin Stevens, catering; David Boyd, technical support; Bob Mizon, Campaign for Dark Skies stand; Jean Dymock, reception and Hazel McGee, photographs and assistance with the meeting report. Total attendance was 39 and feedback from the attendees indicated a high level of satisfaction with the way the meeting was conducted.