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Meetings and events in summer 2017

The main series of meetings held by the Astronomical Society of Edinburgh are its Ordinary Meetings, which feature a main talk by a guest speaker on a topic of general interest. The main talk is often preceded by short presentations by members and by a preview of the month's night sky. Ordinary Meetings are held monthly - except June and August - on the first or second Friday of the month. Non-members are welcome to these meetings, which take place at the Augustine Church Centre. Admission is free, for members and non-members.

Other regular meetings – Imaging Group, in-town or out-of-town observing – tend to be for members only. Occasionally, we also run, participate in, or sponsor events for the public. The annual programme is split in two semesters; the winter semester starts on September 1st, the summer semester starts on May 1st. Any changes to our meeting arrangements will be placed on our website http://www.astronomyedinburgh.org/.

May 5th
20:00, ASE, Church Centre, AUC
Dr Stewart McKechnie
Star image appearance in large ground-based astronomical telescopes
The development of 'Kolmogorov theory' in the mid-1960s advanced understanding of how the atmosphere affects star images formed by large ground-based astronomical telescopes. However, its reliance on untested – and now largely discredited – assumptions about atmospheric turbulence led to unduly-pessimistic resolution expectations (≈1.0 arcsecond) and excessively-coarse telescope optical tolerances, the latter eagerly adopted because of the lower-cost implication. 'Kolmogorov' tolerances ultimately proved mistaken but, before the 'mistake' was recognized, twenty-five years had elapsed and an entire generation of underperforming telescopes had been constructed.
The star images shown in the talk are based on a more recent, more exact theory of star image formation. Developed between 1975 and 1989, this theory requires no 'a priori' assumptions about atmospheric turbulence. Instead, it is based on a generalized atmosphere whose turbulence properties can be established, as needed, from readily measurable star image properties. Contrary to previous understanding, the new theory calls for diffraction-limited telescope optics. It also predicts that, had the largest existing instruments (10-metre class) been built to such standards, in a certain 'optimum' wavelength range they would have routinely delivered 0.05 to 0.15 arcsecond resolution – without use of Adaptive Optics (AO). For next-generation, AO-equipped Extremely Large Telescopes (ELTs) resolution in this wavelength range – now called the 'sweet spot' range – could approach a staggering 0.003 arcsecond.
Dr McKechnie, native of Glasgow and raised in Edinburgh, studied mathematical physics at Edinburgh University, then applied optics at Imperial College, London. He moved to the USA and worked for 32 years as an optics consultant. He now lives in St Andrews and recently published the book General theory of light propagation and imaging through the atmosphere at Springer Verlag.
Jun 2nd
20:00, ASE, Church Centre, AUC
Annual General Meeting
Members only
Followed by a Presidential Address by Seán Wixted.
Jul 7th
20:00, ASE, Church Centre, AUC
Dr Horst Meyerdierks, Astronomical Society of Edinburgh
Cassegrain – who was he?
Today the Cassegrain telescope design and its derivatives are the foremost technology for large professional telescopes and also for a significant segment of the amateur telescope market. It is surprising then that almost nothing was known about Monsieur Cassegrain for over 300 years. At the time his design was published merely as hear-say and faced harsh criticism by Huygens and Newton, the foremost scientists of the period. Although Newton's and Gregory's designs were realised in the 1670s, refractors remained the only practical telescopes for almost two further centuries. Around 1900, mirrors took over and grew larger than lenses ever could. Perhaps it is more remarkable that by then the Cassegrain design had not been forgotten altogether. We still know only very little about its designer. As a major advance, since 1997, we know his initial was not M (for Monsieur), nor N (for Nicolas, really for nescio or "unknown"), but his actual initial was L for Laurent.


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