Society Lecture – Double Bill: The Mercury Transit and Exoplanets + Black Holes and Gravitational Waves – Prof. David Rees

November 9, 2019 @ 7:30 pm – 10:00 pm
Willingdon Memorial Hall
Church St
Eastbourne BN20 9HT

Title: Double Bill: The Mercury Transit and Exoplanets + Black Holes and Gravitational Waves – Prof. David Rees


The Mercury Transit and Exoplanets: A rare transit of Mercury across the face of the Sun will be visible (weather conditions permitting!) from Eastbourne on Monday 11 November 2019.

Mercury will start to move across the face of the Sun at about 12:30 p.m. and continue throughout the afternoon, eventually leaving the Sun’s disc after sunset, as seen from the UK. These planetary transits occur only for Mercury and Venus, which are closer to the Sun than Earth. The events are very rare and the talk will explain why.

As ever, NEVER look directly at the Sun with the naked eye, binoculars or a telescope, as to do so would result in very seriouseye injury and possibly blindness! The transit may, however, be observed safely with a small telescope by:

  • using a special solar filter mounted securely over the front of the telescope to reduce the intensity of the Sun to around 1000th of 1 per cent;
  • projecting an image of the Sun directly onto a white screen. The talk will describe these methods and others.

The next transit of Mercury will not take place until 13 November 2032, so don’t miss Monday’s event!

Just as Mercury sometimes passes in front of the Sun as seen from Earth, so some exoplanets transit their star as seen from Earth and ‘the transit method’, which measures the periodic reduction in the brightness of a star as an exoplanet orbits in front of it, is the most widely used of several techniques that will be described, together with some of the intriguing information that has been discovered about the sizes, orbits and physical properties of exoplanets.


Black Holes and Gravitational Waves: Sixty years ago, a black hole was still a theoretical concept, based solely on Einstein’s theories. Gradually, with evidence from the slowing down of the rotation rate of pulsars, owing to the radiation of gravitational waves and studies of the extreme orbits of stars about the centre of our Milky Way Galaxy and of stellar distributions in the vicinity of the central region of other galaxies such as M86 (a giant lenticular [type S0] – or possibly elliptical [type E3] – galaxy in the centre of the Virgo Cluster), it became almost impossible to argue against the fact that black holes of extreme mass – millions to billions of times the mass of the Sun – exist. Ten binary black hole mergers were then detected through the gravitational-wave events observed during the first and second observing runs of the two Advanced LIGO and the Advanced Virgo interferometers. These events involved an entirely different class of black holes, with masses in the range of only 10 to 45 solar masses.

The Event Horizon Telescope Array (EHTA) is now in the process of successfully imaging the ‘event horizon’ around the massive black hole at the centre of the Milky Way and of other massive galaxies. LIGO and VIRGO have constraints as to what they can observe, owing to the physical size of their baselines and ‘noise’ due to the fact they are ground-based. In the future, ESA’s LISA Space Mission (2033 launch) will extend both the frequency range and the sensitivity to gravitational-wave events. As the ‘frequent’ merger of black holes observed by LIGO and VIRGO has described an important astrophysical/cosmological event that had not been specifically predicted in advance, what new astrophysical phenomena will be revealed when LISA is placed in orbit?


David Rees is Emeritus Professor of Physics at Utah State University, USA. Now retired, he lives in Salehurst (near Robertsbridge), East Sussex, where he designs and builds prototype instruments for NASA, the European Space Agency (ESA), the Japanese Aerospace Agency (JAXA) and other organizations. One such instrument is the MSASI (Mercury Sodium Atmospheric Spectral Imager), which is part of theBepiColombo payload to Mercury (whose two orbiters are due to enter orbit on 5 December 2025). David is currently working on the Aeolus Calibration/Validation Programme for the Aeolus wind-measuring LIDAR (LIght Detection And Ranging) Satellite launched by ESA on 22 August 2018. He also uses a LIDAR systemin his back garden to conduct cutting-edge research into Earth’s atmosphere and wind, and also particulates such as dust from the Sahara. He enjoys playing cricket (for the Kent Seniors team) and regularly observes under some of the darkest skies in Southeast England.

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