Meeting of the Section

Northampton : Saturday, 30 May 1998

R.J. Neville, Journal of the British Astronomical Association, 108 (5), 287 (1998)

This was the fourth meeting of the Instruments and Imaging Section, and as in previous years it proved an unqualified success. Bob Marriott’s formula of thirteen short talks separated by extensive lunch and tea breaks again proved very popular with the audience, which constituted a Who’s Who of amateur and professional engineers, scientists and observers.

Michael Maunder started the proceedings by explaining the construction and operation of a portable system for solar eclipse photography. Although light, the system is very rigid and extremely flexible, and bears all the hallmarks of an experienced photographer.

Graham Salmon, who had journeyed from Truro, followed with a revealing explanation of UVBRI photometry, dispelling the myth that it is mathematically too complex for most observers. However, it is not easy to achieve high precision results, and the photometric accuracy produced is dependent on the care and skill applied in making and reducing the observations.

Norman Walker put forward the professional’s point of view regarding the selective use of photons. Apart from astrometry, he described why the appropriate choice of filters enables real science to be undertaken, in that colour changes in objects – frequently supernovae – combined with a wide range of wavelength responses for various detectors, lead to a wide scatter in derived magnitudes. Norman also showed his multi-filter unit, which achieves accurate positional registration and which is available commercially.

The last speaker of the morning session was Roger Pickard, who presented an account of the operation of the Jack Ells Automatic Photometric Telescope – a remarkable instrument, able to make accurate repetitive measurements over a period of many hours, completely unattended.

A long and leisurely lunch-break followed: some took the excellent fare provided, whilst others adjourned to local hostelries.

Ron Arbour began the afternoon session by describing how he eventually succumbed to an off-the-shelf computer-controlled telescope for his supernova patrolling, how he persuaded it to work ‘decently’, and how he finally discovered his first supernova.

The first of the British supernova discoverers, Mark Armstrong, then spoke about one of his four supernovae – 1998aq. He described his work as an ‘obsession’, but it takes that kind of dedication to not just locate these elusive objects, but also to be the first to announce their discovery. In this case he was particularly pleased at discovering the supernova probably 18 days before maximum light, thereby providing professionals with a very early record of what is usually the poorly observed rising phase.

Tom Boles – another supernova discoverer – talked this time about adaptive optics, and how the technology is progressively entering the amateur domain. Tom gave an excellent illustrated description of how professional systems work and of their ultimate cost-effectiveness. Although the Hubble Space Telescope achieves diffraction-limited resolution because it is above the atmosphere, its aperture is only 2.4 metres, and ground-based systems such as the Keck Telescopes – which cost far less than the HST – can approach this resolution from the tops of mountains.

Nik Szymanek then presented a stunning series of what he called ‘pretty pictures’, in contrast to the subjects of previous talks. With Ian King, he makes regular trips to La Palma and observes from the top of the mountain alongside the William Herschel Telescope and other giants. He described the seeing as normally some of the best on the planet, and his mastery of the photographic art certainly did it justice.

After another long and useful break for tea and discussion, Patrick Miles described an elegant system he has invented for remote detection of a clear sky. The principle lies in registering the difference between upward and downward infrared radiation flow in the absence of cloud cover. Under a cloudy sky there is very little difference, and by setting an appropriate imbalance threshold, the system can indicate clear or cloudy conditions with a reliability of at least 95%. This has important implications for the effective operation of remote or automated telescope systems.

Tom Patrick, of University College London, next presented a fascinating insight into some of the engineering problems encountered while working on space satellites – in particular, the Infrared Space Observatory (ISO), which has recently successfully completed 18 months of observations employing detectors at only 4° above absolute zero. He had to design a stepper motor which would work reliably at these extremely low temperatures at which helium is a liquid. Tom also referred to an unusual set of telescope optics manufactured by another eminent member of the audience – David Sinden.

Bob Neville then had to follow all this with a description of a tilting-plate method for precise image-shifting during the tracking and detection of faint, fast-moving objects. These Near Earth Objects (NEO) have had quite a press recently (1998FX2), and continue to be discovered daily by several dedicated professional systems. The method – or an equivalent system – would enable quite modest telescopes of 20-cm aperture and above to provide scientifically useful astrometric data on these potential hazards.

Michael Maunder next read a contribution by Marcel Le Masson concerning the construction and use of a simple, folding cover for an observatory. Of a design used for sea-going boats, the cover has proved very effective, whilst taking up only a small amount of space.

There then followed two additional short contributions, the first being from Maurice Gavin, who showed the first amateur spectrum of a supernova – a considerable achievement. John Wall then described his latest project: an impressive 30-inch diameter lens, rendered achromatic by a multi-element system close to the focus.

Finally, Bob Marriott briefly described BAA Instrument No.93, a 12¼-inch Calver reflector acquired by T.E.R. Phillips around the turn of the century. Phillips died in 1942, and in 1946 the instrument passed to the Association, since when it has been on loan to Frank Holborn for 17 years and to Alan Heath for 34 years. In July 1997 it was placed in the capable hands of Bob Steele.

The meeting began at 11.00 and finished at 6.45 (slightly later than planned), but most of the 68 participants stayed until the end. Many then headed for The Fish, where lively discussion continued unabated; and for some there was a later adjournment to an Indian restaurant. It had been a long day, but it was a very stimulating and rewarding experience, and we hope to be back again next year!