Report of the
meeting held on
Last
updated
The third
section meeting, hosted by Newbury Astronomical Society,
was held on
Attendees
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.
Speakers
Back
row, left to right: Roger Dymock, Andrew Elliot, Richard Miles,
Front
row, left to right: Mark Kidger, Alan Harris,
The
first speaker was Eamonn Ansbro who
is currently developing a range of telescope facilities at Kingsland
Observatory in
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.
The last of the morning’s speakers was Dr Alan Harris, Senior Research Scientist at the Space
Science Institute in
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.
The "Photometric
Survey for Asynchronous Binary Asteroids" is a
collaborative effort between professional and amateur observers, led by Petr
Pravec of
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.
The last
speaker of the day was Peter Birtwhistle, Assistant Director (Astrometry) described the ‘Tracking
of Near Earth Objects’.
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.
Director