Lecture - 21st December 2017 - 7.30pm
Attaining the ultimate resolution limits of large ground-based astronomical telescopes - Dr. Stewart McKechnie, Member of the ASG
The development of ‘Kolmogorov theory’ in the mid-1960s helped advance understanding of how Earth’s atmosphere affects star images formed by large ground-based astronomical telescopes. But, by relying on untested – and now largely discredited – atmospheric turbulence assumptions, this troubled theory provided unduly-pessimistic telescope resolution expectations (~ 0.5 to 1 arcsec) and prescribed correspondingly-coarse telescope optical tolerances, the latter eagerly adopted because of the lower-cost implication. ‘Kolmogorov tolerances’ ultimately proved mistaken and were abandoned but, alas, not until an entire generation of underperforming telescopes had been built. A more reliable theory of imaging through the atmosphere (1989) in therefore used to address telescope resolution in this non-mathematical Talk – one that does not require ‘a priori’ turbulence assumptions. When needed, the turbulence properties can be calculated from readily-measurable star-image properties using mapping equations derived directly from Maxwell’s equations. Turbulence properties obtained in the above manner (1975–90) consistently indicated that the resolution potential of large ground-based telescopes was not being fully exploited. For the largest of these in 1989 (4 to 5 meter class), the new theory predicted 0.05 to 0.15 arcsec resolution in a certain ‘optimum’ wavelength range – a range later confirmed by experiment, now known as the ‘sweet spot’ range. However, to fully realize the predicted ~10x resolution improvement would now require diffraction-limited telescopes! For next-generation (~2025) AO-equipped Extremely Large Telescopes (ELTs), resolution at sweet spot wavelengths could approach a staggering 0.005 arcsec (5 mas).
Biography: Born in Glasgow. At age four, my family moved to Edinburgh, where I spent the rest of my upbringing living at 10 Observatory Road. Attended George Watson’s College and became interested in astronomy as a teenager. Wishing to improve on my meager 1-inch draw-tube telescope, I ended up building a 6-inch reflector telescope. I was greatly amazed when it actually worked. After leaving school, attended Edinburgh University, obtaining a B.Sc. in Mathematical Physics. (Took courses given by the now celebrated Prof. Peter Higgs!) Then went to Imperial College (IC), obtaining a M.Sc. in Applied Optics followed by Ph.D. in light scattering. My work on imaging through the atmosphere with large telescopes began in 1975 while doing post-doc research at IC. In 1981, a job opportunity took me to the US where I continued to live and work as an optics consultant for the next 32 years. Much of this consulting related to light propagation and imaging through the atmosphere. I retired in 2009, only to spend the next 6 years writing the book, “General theory of light propagation and imaging through the atmosphere,” Springer Publications, Sept., 2015. In 2013, my wife and I decided to return to the UK, choosing to live in St. Andrews where we had spent many fun holidays.
Location - Room 6.41 Royal College, Strathclyde University. Access is via the Montrose Street entrance, take the lift to Level 3, exit the lift and take the 2nd set of steps on your left, go through the double glass doors. Room 6.41 is on your left approximately half way along the corridor.
Public lectures for the 2017-2018 session
The ASG's free public lectures for the 2017-18 session are as follows, the dates and titles are shown below. They are normally held in Room 6.41 Royal College, Strathclyde University unless otherwise advised. Access is via the Montrose Street entrance, take the lift to Level 3, exit the lift and take the 2nd set of steps on your left, go through the double glass doors. Room 6.41 is on your left approximately half way along the corridor. The lectures start at 7:30pm and are preceded from 6:45pm by either a presentation on the month's skywatching highlights or by a social event giving you the opportunity to meet other members.
The lecture programme for the 2017-18 session is as follows:
|Thursday 21st September 2017||Should We Fear Solar Tornadoes?
The Eric Tomney Lecture
Dr. Nicolas Labrosse, Senior Lecturer in the School of Physics & Astronomy at the University of Glasgow
|Thursday 19th October 2017||Radio Astronomy from your Back Garden
Prof. Graham Woan, Professor of Astrophysics at the University of Glasgow. Director of the University Observatories and head of the Astronomy and Astrophysics research group in the School of Physics and Astronomy
|Thursday 16th November 2017||The Universe is full of noises: a new perspective from gravitational waves
Mr. Daniel Williams, PhD candidate and researcher working in the Institute for Gravitational Research in the School of Physics and Astronomy at the University of Glasgow
|Thursday 21st December 2017||Attaining the ultimate resolution limits of large ground-based astronomical telescopes
Dr. Stewart McKechnie, Member of the ASG
|Thursday 18th January 2018||METI – Messaging to Extraterrestrial Intelligencies
The Tannahill Lecture
Dr. Alan Penny, Honorary reader and visiting scientist in the Astronomy Group of the School of Physics and Astronomy, University of St Andrews
|Thursday 15th February 2018||Members' Night Talks|
|Thursday 15th March 2018||The Gaia Mission: unravelling the composition, formation and evolution of our galaxy
Dr. Nick Rowel, Researcher and developer with the Wide Field Astronomy Unit at the Royal Observatory of Edinburgh
|Thursday 19th April 2018||The Sun's Evolving Magnetic Skeleton
The Leon Davies Lecture
Prof. Clare Parnell, Professor of Applied Mathematics, School of Mathematics and Statistics, University of St Andrews
|Thursday 17th May 2018||Asteroid Exploration and Exploitation : from nanoprobes to asteroid engineering
Prof. Max Vasile, Professor of Space Systems Engineering, Department of Mechanical and Aerospace Engineering, University of Strathclyde
|This lecture will be followed by the Society Annual General Meeting|