To study and encourage popular interest in all branches of Science.

Newsletter August 2011

Dear Member,

The Annual General Meeting took place on Thursday June 16th. In his report the President said that after last year's activity in preparing for the Observatory centenary he had been expecting a 'quieter' year. However, this proved not to be the case and 2011 turned out to be another record year for the Society. Our participation with the BBC2 television programme 'Stargazing Live' in January introduced the Society's activities to a nationwide audience on 'prime time' television and was directly responsible for our subsequent membership increase to 133, itself a record. Despite appallingly bad weather coinciding with the programme, visitor numbers to the Observatory were high and the total exceeded 1500 for the year - another record. Donations to the Observatory Fund for the year amounted to over £1000 – yet another record and equally important, the publicity gained from our exposure on television has recruited several younger members to the Observatory team. The President thanked all those who took part in the programme of extra open nights at the Observatory and particularly to Simon Lang and all those members who braved the weather at dawn in January on Parliament Hill to provide the BBC camera crew with some footage – even if it did not actually include spectacular images of the partially eclipsed sun rising above the London skyline! But, as is so often the case, our weather often triumphs over, but never entirely dampens our members' enthusiasm.

During the session Dr. Leo McLaughlin stated his wish to resign from the Council for reasons of health. We are sorry to lose him but we thank him for his help in the past and hope that he might return at some future time. Council proposed Dr. Kevin Devine to fill the vacancy. As there were no other proposals received from the membership, your Council, elected at the AGM is as follows:

Secretary Dr. Julie Atkinson
Treasurer & Membership Secretary John Tennant
Programme Secretary Jim Brightwell
Ordinary Members (max 5) Martin Williams, Peter Stern, Julia Daniels
Roger O'Brien, Dr Kevin Devine

The President then announced that Council proposed that Ray Softly be granted Honorary Membership. Ray, who must be one of our oldest members, was for decades the backbone of the Natural History Section during which time he accumulated an unrivaled knowledge of the fauna and flora of Hampstead Heath. Ray now lives in retirement near the Essex coast. The membership applauded Council's decision and they all wish Ray a long, happy and healthy retirement.

Enclosed with this Newsletter is the new Programme card for the 2011 – 2012 session. I am sure you will agree that as ever our Programme Secretary has managed to produce an interesting and wide ranging series of lectures for the forthcoming year. Jim wishes me to remind you that he is always interested to hear from members regarding their ideas for subsequent lectures. If you have attended an interesting talk and think it might be of interest to the membership, let him know about it and if possible provide contact details.

The new session of lectures begins on Thursday September 15th when Dr. Michael de Podesta MBE from the National Physical Laboratory will talk on: GLOBAL WARMING FROM FIRST PRINCIPLES
I look forward to seeing you at the meeting.

Finally, a reminder that subscriptions this year remain the same despite inflation in most other areas, and represent excellent value for money; they are due on October 1st. Please assist our Hon. Treasurer by renewing in good time. Better still – renew by Bankers Order and save money and the need to remember.



Peter R Wallis

Several studies and computer simulations have been carried out over recent years to explain how the planets and asteroids in the Solar System formed. Astronomical advances have also enabled the discovery of many extra-solar planets. So I was very interested to read a recent paper in Nature [1] suggesting how our planetary system may have evolved.

It was shown 25 years ago [2] that giant planets embedded in a gaseous planetary disc carve annular gaps as they grow and also migrate inwards. This seems to be consistent with observations of extra-solar planets, which are usually found close to their star, but this may well be because these are the ones that are easiest to detect! More recent studies and hydrodynamic simulations have shown that such an inward migration occurs in a time-scale of 100,000 years. But, surprisingly, the direction of migration may reverse if two giant planets are trapped in a resonance.

Walsh et al apply this to the case of Jupiter and Saturn in our solar system. They postulate that Jupiter initially formed at 3.5 AU or more from the Sun (1 AU is the distance of the Earth from the Sun) and migrated inwards to 1.5 AU. Saturn follows and becomes trapped in a 3:2 resonance with Jupiter, causing the migration of both to reverse. They recede and, through other resonances, push Uranus and Neptune out too.

It is obviously very difficult to prove that this was what occurred 4.5 billion years ago. However, the calculated consequences may provide support for the hypothesis. Firstly, our giant planets are clearly much further away from the Sun than those extra-solar giant planets so far discovered (commonly at 1.5 AU from their stars). Secondly, their outward migration has left an inner disc of planetesimals truncated at about 1 AU, a suitable environment for the subsequent formation of the rocky planets Mercury, Venus, Earth and Mars. Walsh et al performed 8 simulations of the formation of these planets over a further 150 million years. Their results match the positions of the planets and, in particular, reproduce the large mass ratio between Earth and Mars.

They also study the effect of the Jupiter and Saturn migrations upon the asteroid population. The volatile-poor planetesimals end up preponderantly in the inner asteroid belt. Their simulations show that many of the volatile-rich planetesimals are deflected into eccentric orbits crossing the planet-forming region near 1AU; they could well have represented a source of water for Earth.

It seems that we may well have a lot to thank Saturn for!

[1] Walsh K. J.,Morbidelli A.,Raymond S. N.,O’Brien D. P.,Mondell A. M., "A low mass for Mars from Jupiter's early gas-driven migration", Nature, 14th July 2011 Back
[2] Lin D.N.C. & Papaloizou J., "Orbital migration of protoplanets", Astrophys. J, 1986 Back



Doug Daniels

Although astronomers have for many years suspected that planetary systems other than our own must exist, it was not until the 1990's that evidence of their existence was confirmed. To date 1,230 systems have been identified surrounding stars within a radius of about 100 light years, and every year more are being discovered.

The first candidate was a rather unlikely one, in that the parent star involved was a Pulsar, the remnant of a Supernova. The Pulsar PSR 1257+12 is apparently accompanied by multiple planets. It is open to conjecture as to whether these planets are in the process of being formed from the material ejected from the Supernova, creating a nascent system or if they are merely the old cores, the cinders of previously existing planets that were destroyed by the blast from the supernova explosion.

The first 'Sun like' star discovered to be accompanied by a planet was 51 Pegasi, discovered in 1995. The first system with multiple planets to be discovered was the star Upsilon Andromedae and there are now at least 50 systems known to be supporting multiple planets. Of these the best known is the red dwarf star Gliese 581 twenty light years distant in the constellation Libra. At least 4 planets are known to orbit this star and one of them Gliese 581c is a possible contender for a planet orbiting in the so called 'Goldilocks' zone where temperatures would allow liquid water to exist. Gleise 581c has been described as a 'Super Earth' with a diameter of about 19,000 kilometres. But this is small beer compared to the planet in orbit around HD43848 which is estimated to be nearly 8,000 times the mass of the Earth.

Because of their relatively small size compared to their parent star, exoplanets only reveal their presence indirectly. They are detected when they transit their primaries in our line of sight, or by their gravitational effect on their parent star detected by redshift in the star's spectrum. However, the Hubble Space Telescope has recently obtained the first direct image of an exoplanet orbiting the star Fomalhaut. It can be seen clearing a path in the dust disk surrounding the star.

The majority of the exoplanets so far discovered are massive gas giants which appear to orbit close to their primaries. Many have been designated 'Hot Jupiters' and such systems are vastly different to our own. If planets occur naturally around pulsars, red dwarfs and main sequence stars, it begs the question do they exist around most stars? If our present ideas concerning the formation of stars and planets are correct, then planetary systems ought to be quite common. It seems that we still have a long way to go before we fully understand the complex processes and interactions that take place during the early stages of planetary evolution in protoplanetary disks. However, one thing is certain - there must be a whole lot of planets out there just waiting to be discovered.



Doug Daniels

Of course I'm biased. I belong to a generation that inhabited a world long before computers were commonplace. In my heyday there were not even such things as electronic calculators, and 'windows' were panes of glass that you looked through. The best calculating aids we had were slide rules and a book of log tables - oh yes and a set of tables drummed into our brains at the age of six plus, so thoroughly, that if you ask us to multiply 9x8, the answer 72 is delivered instantly without even having to think about it!

Today it seems everything just has to have a computer attached to it otherwise it is just not worth considering. Astronomical telescopes are no exception.

I recently spent an interesting yet frustrating few hours with a good friend who had just taken delivery of one of these small computerised 'Go-To' telescopes. Apparently it was able to automatically find upwards of 5,000 celestial objects all by itself and was designed to make 'finding celestial objects easy for the beginner.' Some mistake surely!

After inserting a handful of batteries, we switched it on. It asked us to enter the date and time; we complied. A message was spelled out on the handset warning of the dangers of looking at the Sun, spelled out at such an interminably slow speed that I was already beginning to feel my arteries hardening. Why for heavens sake? We have already told the wretched computer the date and that the time is 23.00 hrs UT - if it's that damned clever it should know that the sun is below the horizon! It then asks us if we would like a 'tour of the solar system?' No we would not we just want to look at the Moon! It proceeds to do it anyway. Motors hummed, the telescope swung wildly up and down and round and round, finally coming to rest pointing down towards the ground presumably attempting to home in on the Sun to justify its earlier warning.

After several abortive attempts to encourage it to point to the Moon my patience had run out and I switched it off, unclamped it and pointed it at the Moon manually. But even that was not so easy as the wretched device uses a built in diagonal and has no finder. I would hate to try to point it at something really faint, you would just have to rely on its computerised functions to do this and judging by our earlier attempts it could take all night to find the Andromeda Galaxy. O.K. perhaps I'm being too quick to judge and it will take some time to become thoroughly acquainted with its little foibles; hopefully before its batteries go flat.

But I still maintain that such a device could lead to enormous frustration for a real beginner. It's only a 70mm refractor for heavens sake! A simple alt-azimuth mount on a tripod would allow you to point it at the Moon and get an instant result without spending hours reading the instruction manual and then trying to identify certain stars to set its position. An absolute beginner would probably not be familiar with these stars anyway. Before even attempting to use a 'Go To' telescope it would be better to spend a few months getting acquainted with the night sky with a simply mounted telescope or a good pair of binoculars and a star map.

And whilst I am having a rant on the subject of unnecessary computers and telescopes, I strongly object to fitting computers to antiques. I recently visited the old Royal Greenwich Observatory and was appalled to discover that they had 'computerised' the historic 28-inch refractor. Using this wizard 'strap on' electronic gizmo meant that it only took them about 10 minutes to locate the Moon - a task that could have been accomplished manually in about 30 seconds by just squinting through the finder. I thought that computers were supposed to make life easier! Some mistake surely!

It's the same at Mill Hill Observatory. The 18/24-inch Radcliffe refractor, a magnificent example of Victorian engineering constructed by Sir Howard Grubb, is now draped with cables and electronics and thoroughly 'computerised.' I'm sorry but I just do not agree with this. I understand that students need to learn how to manage a computerised telescope but attempting to modify an ancient instrument is the wrong route to take. To see all this electronic paraphernalia attached to the works of traditional makers such as Grubb and Cooke is, to quote our esteemed heir to the throne: "Like seeing a monstrous carbuncle on the face of an old friend." Computers and brass fittings do not blend comfortably. If you must teach on a computerised instrument, and of course today you probably must, use one specifically built for that purpose, don't desecrate the works of historic telescope makers.

O.K. rant over. I shall now return to my cave, light a fire by rubbing two sticks together, suck the marrow out of the bones of a woolly rhinoceros and pay tribute to old King Ludd.


Home Page


Last updated   27-Jan-2018