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Dr. David Asher Talk

David Asher

The following report documents the recent EAAS meeting and fascinating talk by Dr. David Asher of Armagh Observatory.

Third Meeting Of The Third Season

Autumn has arrived, the leaves are falling from the trees and the clocks have gone back one hour resulting in darkness falling at a more convenient hour for stargazers. Autumn is a great time of year for observing the night sky providing us with several celestial firework displays during the month which time themselves nicely with our special guest speaker however more about this in a minute.

The third EAAS meeting of the new season took place on Monday Nov 6th with a rich gathering of attendees and a selection of new members. The meeting began with our chairman Mark Stronge informing members of the latest sky events and news on the up and coming Leonid meteor shower outburst and a possible but yet unconfirmed enhancement of the Monocerotid minor shower which will take place in the days after its famous counterpart. Before our guest speaker took to the stage Mark introduced the first of a new series of short talks by EAAS members aimed directly at beginning observers.

An Introduction To Constellation Mythology

New up and coming EAAS member Eamonn Keyes began the new series of short talks. Eamonn is a very enthusiastic visual observer with a keen interest in deep sky observing and his talk was based on this subject with the beginning observer in mind. His chosen subject was titled ‘The Perseus Myth & The Night Sky’ which Eamonn delivered in a clear confident style. Mr Keyes words took us on a journey which merged the history of constellation mythology with modern day star highlights in the constellations which are within the range of small amateur telescopes, binoculars and even the naked eye such as the ‘Double Cluster’ and ‘Andromeda Galaxy’ which were complimented by a range of constellation maps which covered his subject targets within Perseus, Cassiopeia, Andromeda and Cepheus.

A ‘keye’ highlight (excuse the pun) was his fascinating in depth coverage of the mythology which surrounds these famous star figures, a story which was underlined by vivid narrative and imagery, some of which was not for the faint of heart I can tell you. Even experienced armchair and visual astronomers learned something new from his talk. It was evident that Eamonn had done extensive research into his topic and rehearsed his delivery thoroughly before taking to the stage. Thanks to Mr keyes for starting this new trend and we very much hope to hear future talks from our new engaging and pro-active observer.

Introducing Dr. David Asher

Our very special guest speaker tonight was Dr. David Asher from Armagh Observatory who delivered a talk on ‘Dirty Snowballs, Sudden Meteor Outbursts & Asteroid Flybys’ but first a little background on our speaker…

Dr Asher is one of the world's leading experts in Near Earth Objects (NEOs), currently dividing his time between Armagh and Japan where, at the invitation of the Japan Spaceguard Association, he is working at the Bisei Spaceguard Centre, Japan.

However, in recent years he has also worked closely with Robert Mc Naught of the Australian National University, in predicting so precisely, the Leonid Meteor Storms to within a few minutes.

Dr Asher was born in Edinburgh, and between school and university got a kind of student vacation job with Dr Victor Clube and Professor Bill Napier at the Royal Observatory Edinburgh (ROE). It was here that he gained his interest in astronomy.

Later, he did his research degree under Clube, and his PhD thesis was on the Taurid meteor stream. He then went to work with Dr Duncan Steel's near-Earth asteroid programme in Australia, (since closed down by the Australian Government), learnt what a telescope was, (his words!), and got to know Robert Mc Naught.

It was during his time in Australia that he discovered a number of asteroids one of which has recently been named (16693) Moseley in honour of Terry Moseley, former President of the Irish Astronomical Association, and good friend of the EAAS.

His current job at Armagh is to work with the Director, Professor Mark Bailey, doing theoretical (computational) studies in solar system dynamics. The research project is about sun-grazing and Jupiter-grazing objects in particular, such as comets and asteroids.

A Superb Talk From An Imminent Man

Dr. Asher is no stranger to delivering talks and lectures on astronomical subjects and this was very apparent even to new members when he announced his four section talk which was based on his life time of work within the complex and fascinating world of solar system dynamics. Dr. Asher spoke with a very clear direct voice and without any notes at all, which was hardly surprising as David is a world authority within his field of research. We were very fortunate to have Dr. Asher give us a talk during November, was it luck? or an extreme coincidence? that one of the most exciting meteor showers would take place during this period and that we would have a world expert whose career was based heavily on this meteor shower with us at the same time? Whatever the reason the timing was great for amateur astronomers.

A Bananarama Leonid Meteor Shower Outburst!

So what was all the fuss about? Every year during November the Earth ploughs the debris trail of comet 55P/ Temple–Tuttle which produces the annual Leonid meteor shower which takes place on Nov 17/18th. The progenitor comet returns to the inner solar system every 33 years which often heralds a possible Leonid storm however at the moment the shower typically produces a very paltry rate as the comet is nowhere near us however this is where our story takes a turn and David’s expertise comes into play.

Comets (Dirty snowballs – a term coined by Fred Whipple) or as David informed us ‘Icy conglomerates’ if you want to sound smart are the source of meteor showers. Dust particles (meteoroids) do not leave a cometary nucleus uniformly but instead are ejected from its parent body in the form of jets or fans which over time form a trail around the sun. Once (in some cases twice) a year the Earth swallows up these dust particles which burn up in our atmosphere and flare to incandescence due to friction producing a meteor or ‘shooting star’. Sounds simple enough however it is quite a complex process as Dr. Asher introduced us to the world of orbital dynamics. Due to non gravitational forces and perturbations of the major planets the Leonid meteoroid trail can spread out diffusely our have a dense morphology when calculations take into consideration the number of revolutions the stream makes around the sun (age). Making these calculations with comparison to the behaviour of previous streams during the 1960’s David was able to provide us with a forecast for this years Leonid meteor shower. On Nov 18/19th at 04.45 UT his modelling predicts that the Earth will encounter a dense stream of small particles during the pre dawn hours producing a brief outburst of meteors with a ZHR of approximately 120 and what’s more, observers in N. Europe are perfectly placed for the encounter!

Dr Asher explained this process in a very clear and easy to understand fashion and even used an unorthodox method to engage his audience. Like a meteor he produced a bunch of bananas seemingly from nowhere and chose the straightest banana in the bunch which he pealed in front of his startled audience. Next he produced a large kitchen knife and carefully cut a cross section through the banana at an angle then held it face on to the crowd to give us a visual demonstration of the shape of the dense Leonid meteoroid stream we would encounter. This was a very delightful and humourus way to educate society members – and it worked!

The Earth As A Dart Board

Dr. Asher then introduced us to a subject which is both fascinating and with profound implications to human civilisation. Cosmic impacts! Planet Earth is a moving dartboard and the darts (comets and asteroids – NEO’s) are continuously passing through our cosmic back garden. David brought to our attention a list of REAL near Earth asteroids and provided us with the currently accepted statistics on how often we should encounter an object of a given size and energy yield. Some of these objects are only meant to be seen once every 30 years and others on much longer time scales, yet here was a list of objects which statistically should not be here at all. These objects defy the rules and David put forward his case that the NEO impact risk is far greater than had we currently realized. After all, these were KNOWN objects but what about the objects which we do not know about which are most likely just as common in frequency? It was certainly a sobering concept and food for thought.

From Meteors To Occultations

To round up this comet, asteroid and meteoroid connection David talked about asteroid occultation’s. This happens when an asteroid passes in front of (eclipses) a background star causing the star to vanish for a short time. Why is this important? If many accurate timings are made by various observers at different locations across the asteroids shadow track then this information once corrected for atmospheric seeing conditions can be used to determine the actual shape of the asteroid itself! As it so happens Dr. Asher described his recent trip with fellow Armagh Observatory researcher Dr Apostolos Christou to Donegal to image and time such an occultation with a near Earth asteroid. The observations were a complete success and David happily displayed the results and asteroid shape on the overhead for everyone to see. This is an inspiration to other amateur astronomers with the appropriate equipment to get out there and make these accurate timings which are so useful to science. This is the ultimate primer for a ‘Pro – Am collaboration’.

The talk ended with a fascinating question and answer session. I think everyone would agree that Dr. Asher delivered an outstanding and fascinating talk which was fuelled by passion and a professional manner which could only come from a true master of his field. On behalf of the EAAS I wish to thank Dr. David Asher for a memorable and fascinating night!

Martin Mc Kenna

2006 Leonid Meteor Shower Observing Report