Extra Solar Planets

A talk by Dr. Robert Smith on Wednesday 17th March

Robert Smith is a lecturer in Astronomy at the University of Sussex, with particular interest in Spectroscopy and Interacting Binary Stars.

He introduced the talk by saying that although planets around stars systems beyond the Solar System cannot be seen directly, over a hundred planets have been detected around ninety stars.  Of these planets, all but one have been discovered by monitoring the "wobble" of the host star.  At present, the sensitivity of detecting methods limits the size of these planets to Jupiter of even Saturn sized objects.

Robert defined a star as greater than 0.8 solar masses (about 80 Jupiter masses), powered Hydrogen fusion, with Brown Dwarfs (about 13 Jupiter masses) powered by some Deuterium fusion.  No one really agrees, but it is suggested that a planet is anything less than 13 Jupiters.

He then looked at various methods used to search for Extra Solar Planets

Interferometery  - both ground based and space missions using radio are investigating, but there have been no successful results so far.

Measurements of the wobble of a star have produced many positive finds, although he went on to say that this method requires incredibly accurate position measurements, using Quasars as the most accurate background reference, as in any appreciable time, they move less than anything else in the sky.  Using this method Sirius B was one of the first stars to be detected as having planet orbiting around it.

Radial Velocity is another method being used in the search.  This method looks at the Doppler change as the star rotates with its companion large planet.  This requires incredibly accurate Doppler measurements, and its greatest chance of detection is if the plane of the orbit is in line with the observer.  Many stars appear to vary in this way because of the nature of stars gaseous changes, so the planet would have to be relatively quite large to be distinguishable.

Transit detection involved the orbit of the relatively large planet transiting the parent star as seen from by the observer.

The last method Richard referred to was Gravitational Lensing.  The light from a distant background star could be diffracted by the gravitational effect of a closer star.  If this closer star has a suitable planet orbiting it, the light from the distant star as the closer star passes in front of it would show a "blip" on the light/time graph.  The big disadvantage of this method is that the pass may only be seen once due to the star's movement, and could not be verified by observing other blips.  The size of the peak of the blip would indicate the size of the nearer stars planet.

Richard concluded this part of his talk with the story of one of his graduate students; Kevin Apps who has became noted for much work on the detection of Extra Solar Planets.  He had emailed Marcy and Butler in the USA whose work was already well known, requesting a list of the 300 target stars for the 10 metre Keck telescope on Mauna Kea.  He received the list from Geoff Macey, but found 30 of these stars to be unsuitable because they were either too big or were binary stars.  Richard was astonished to discover that Kevin had told Geoff Macey of these, who then asked for suggested replacements.  Kevin then provided 30 new targets and now Macey began to take Kevin seriously, and he went on increasing the list by another 400.

Kevin Apps went on to observe at the Lick observatory in April 1999 and then in August 1999 he observed with the Keck telescopes.

Current finds (to last year) had increased to 103 planets with masses of 0.12 to 16.9 Jupiter masses.  36 of these were "hot Jupiter" type planets, which orbited very close to the parent star.  Two thirds of the planets had eccentricities greater than Jupiter and 12 systems had multiple planets.

Since the search has only been in progress for a few years, only planets with periods less than this time can be determined, and as time goes on, more planets are certain to be discovered.

Only one transit type orbit had been discovered and confirmed by the Hubble Space Telescope.  The orbit took just 3.5 days, and the drop in light caused by the planet passing in front of the star lasted only 0.1 of a day.  There is another possible transit type planet with an orbit of 1.2 days, but is waiting to be confirmed.

Richard concluded this talk with a brief look to the future.  Continuing searches using radial velocity methods hope to find lower mass planets.  Gravitational Lensing is statistical only.  Direct imaging is difficult from the ground, but space-based astrometry will be possible with the launch of "Darwin" possibly in eight years time.  This incorporates 6 space craft fixed relative to each other very accurately, and will use high resolution infra-red interferometry.

Richard suggested a worthwhile web site called OPM (l'Observatoire de Paris et Meudon) www.obspm.fr where there was a lot of useful astronomical information to be found.

      This was a well constructed talk of what could have been a complicated subject, but was explained in a pleasant and interesting way using computer graphics and a digital projector.


         At the next meeting on Wednesday April 21st  2004, the speaker will be Peter Gill.  His talk is called "Talk on the Moon".

      As usual, the meeting will be held in the Drama Studio at Uplands College.  The doors open at 7.15 and the meeting starts at 7.30 prompt.





   Paul Treadaway has sent an interesting email:

 I visited the Observatory Science Centre at Hertmonceux, the former home of the Royal Greenwich Observatory. We were talking with Sandra Voss  s.voss@the-observatory.org 01323 832731) and she says that astronaut David Scot will be giving a talk on May 13th, and signing his book. David was aboard Apollo 15 and drove on the moon. The event is a late entry, not shown in the function list (yet); see www.the-observatory.org , and is only £3 for entry.

Paul Treadaway


           There will be Observing Sessions on the following Fridays:

23rd April

  21st May

      The sessions meet at 7.30 pm in the Crow and Gate pub, about a mile south of Crowborough on the A26 main Uckfield road.  Then at 8.00 pm the group move onto Ashdown Forest with Sean’s and the Society’s telescopes and possibly others.

      Sean Tampsett suggests that interested members phone him between 6.00 pm and 7.00 pm to make sure the session is going ahead.



      The Treasurer now reports that we now only have four of last year's members who have not yet renewed their subscriptions, and we are pleased to welcome two new members;

Michael Berks and Jan Drozd.  We hope they will enjoy their membership with us.



Duncan Goulding

Duncan has been instrumental in arranging for the Isle of Man Astronomical Society to get a 28" mirror for the Foxdale Observatory site, IOM.  The mirror had been the property of Duncan's friend Harold Robin and Duncan was the 'go between' for both the Manx society and the Robin's family.  I should mention that Duncan had originally suggested that perhaps the WAS should take on the big mirror but it was realised in the conversations that he had with myself and others that this could well be 'a poisoned chalice'.  I know that it gave Duncan great pleasure seeing the mirror off to the financially well-supported society in the Irish Sea.

       Incidentally, it was a mirror from Harold Robin that was installed into the observatory at the Isle of Thorns site.  Duncan was very much involved with this project.  I am sure that Duncan would wish me to make clear that the installation of the equatorial mount for the 18" however was not his responsibility for if it had been perhaps the builders would not have made such a drastic error with regards the setting of the pier!   Duncan and his wife Thelma often participated in out reach programs for the public and the disabled.  At the Harold Robin Community Study Centre, Isle of Thorns, Duncan would give demonstrations of mirror making techniques and explain the rather esoteric Foucault test to people of all ages and abilities.  Duncan was very saddened when the site, previously operated by Sussex University was taken over by the Cats Protection League.  Duncan knew that it was only a matter of time before free access to the telescope would be curtailed by the new owners who did not appreciate nor indeed want a research telescope.  In spite of much canvassing and letter writing, Duncan's worst fears have sadly been realised.  I recall that Duncan was hoping that perhaps some of the projects he was involved in might continue at the at Ringmer College site near Lewes.

      On a happier note, Duncan, Thelma and Christine Jones voluntarily operated a small organisation called 'Heavens Above'.  Basically this group encouraged schools to build telescopes!  The idea was for children working with teachers and parents would actually grind, polish and figure telescope mirrors to be installed into telescope tubes.  I understand that it was primarily Duncan's guiding hand that steered these projects.  Several schools in the county of East Sussex have benefited from this.

      Before his illness Duncan was a fully participating member of the society.  He and Thelma enjoyed the fêtes and shows at both Wadhurst and more recently Speldhurst.  Duncan would always attend committee meetings and the committee in turn felt that he should be asked if he wished to take the position of 'technical advisor'.  Given his willingness not only to listen but also to help members, this was a perfect role for him.  Many members of the Society will remember Duncan offering the use of his extensive metalworking equipment to anybody who was building a telescope or parts thereof. He also offered technical advice to anybody who felt they needed it. Duncan would always carry with him a note pad and pencil and would doodle magnificent near-technical drawings of focuser mounts, spiders (secondary mirror supports) and these drawings would then eventually make their way into one of three engineering workshops at his home in Rotherfield.  Duncan made several items for the society telescope including the expertly crafted spider.  It was in his Aladdin's caves of engineering that Duncan and his colleagues would produce bespoke high light intensity devices to be used by medical researchers in the field of cancer diagnosis and treatment.

  The interest in astronomy was of course a lifetime pursuit and it is only very recently that his permanently sited garden telescope has been taken down from its plinth in his garden.  I vaguely recall that this telescope has been in use from his garden for over 50 if not 60 years!  I am pleased to tell you that Duncan made a gift of this telescope to his former old school, Cranbrook.  I hope they too will enjoy safe observations of the sun with its un-silvered mirrors.

  Duncan will be sadly missed and I extend my sympathies to Thelma and her family.

Murray Barber




Chairman: Murray R. Barber        01892 654618


Treasurer: Ian Reeves                        01892 784255

Editor:        Geoff Rathbone           01959 524727


Publicity &

Web Site:  Michael Harte              01892 783292


Dir. of

Obs:    Sean Tampsett                       01892 667092