The Origin of comets and the Oort Cloud - October 3rd 2005

Today EAAS members observed two star attractions. The first was a partial solar eclipse that commenced early on Monday morning. A collection of dedicated observers waited under the clouds from Mark Stronge’s home despite the poor weather forecast. As the eclipse neared its end their patience was rewarded with a short glimpse of the moon biting into the suns disk through light clouds and even obtained images within that short window of opportunity. The EAAS were among a small group of observers who seen the eclipse throughout Ireland. While most other observers were clouded out they did notice a significant drop in light and temperature during mid-eclipse. The meeting began with EAAS webmaster Mark Stronge giving a short verbal summary of the eclipse watch complimented by a selection of great images!

The second star attraction was our guest speaker professor Mark Bailey from Armagh Observatory who gave a stunning detailed talk entitled ‘The Origin of Comets and the Oort Cloud’. Marks presentation began with an overview on what comets are made from, how they formed while touching upon the subjects of impacts and the role of comets in the early Earth's history. On display we could see four samples of cometary nuclei and an overview of some celebratory comets such as Shoemaker Levy 9 and great comet Donati.

With the basics covered professor Bailey’s talk evolved into an in depth cutting edge discussion on the theories of the Oort cloud. The Sun's sine wave motion around the galaxy could periodically bring our solar system through hazardous territory near the galactic plane where the outer region of the Oort cloud could suffer perturbations due to the close approach of other stars and interstellar clouds that could generate a ‘comet shower’ to possibly lead to impacts and mass extinctions on Earth!

We learned how Jupiter, the solar system’s vacuum cleaner, is the gravitational monster that transforms long period comets into orbits of short periods which is the mechanism that brings about the Jupiter family of comets. Of notice was his tennis racket analogy he used to show members how Jupiter’s gravity can capture comets or slingshot them out of the solar system altogether!

The subject of comet orbits got a good overview where yet again Mark’s ability to visualise astronomical concepts was put to good use. Using his ‘pointer’ he described how the oscillating affect of a perturbation within the Oort cloud could drastically affect the perihelion position of a long period comet as it enters the inner solar system, this certainly helped me understand the orbital mechanics better than I have done previously.

As the talk approached its end, professor Bailey introduced us to his theory on the ‘missing’ comets compared to the observed comet flux and enlightened us on the optically invisible cometary nuclei that may account for the observed discrepancy in the data which was fascinating in it self. Over all the talk was an excellent well presented experience that educated us all about this important subject.

At the end of the meeting EAAS member Andy Johnston presented professor Mark Bailey with an Andrew Trimble Memorial crystal paperweight. Mark had given a talk to the very first memorial lecture before the paper weights were produced and he received this on behalf of the Trimble family and the club members for his lecture in 2003.

This is the third excellent talk he has given for the EAAS and we look forward to more in the future. On behalf of the EAAS... thanks Mark!


Martin McKenna
EAAS Member

Mark Bailey hails from Burnham in Buckinghamshire. He has had a distinguished career in astronomy and physics, taking his first degree in Physics with Theoretical Options at Cambridge University before going to the University of Sussex where he read a Masters in Astronomy. His Doctoral research took him to the University of Edinburgh, and following this he spent a period at University of Manchester as a Research Fellow. Just prior to being appointed Director of Armagh Observatory in 1995, he was lecturer and Reader in Astronomy at Liverpool’s John Moor’s University. In 1996 he was honoured with a Professorship from Queen’s University Belfast.

In recent years he has been involved with “Spaceguard” an organization set up to investigate Near Earth Objects, asteroids that stray too close to the earth with the potential danger of hitting. He has also been honoured by the International Astronomical Union with the naming of asteroid (4050) Mebailey, and is currently a Council Member of the Royal Astronomical Society.


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Last Updated : Tuesday, October 11, 2005

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