Members' Talks - 29 May 2025

A fascinating and enlightening evening with three very different talks.

It’s always good to hear from our members - whether just in conversation, through our survey, or, as on Thursday 29 May 2025, in these three excellent talks.

Matthew’s talk about his MSc thesis, Investigating exoplanet obliquities in young star systems, sounded at first a bit technical, but in fact Matthew spoke in a very accessible way. He explained the processes and the details of how he wrote his thesis very clearly. He told us about the Rossiter-McLaughlin effect, which is a way of measuring the angle of an exoplanet’s orbit around its star, and, along with other techniques, is an important part of identifying exoplanets as they orbit. He talked us through how planets form in protoplanetary discs around stars and explained why the exoplanets we find are often very close to their companion stars, and why they are commonly called “large Jupiters”.

Brendan told us about William Rutter Dawes, the unsung hero of Victorian astronomy. It was clear from his talk that he was very inspired by this man, who, it turns out, lived not far from where Brendan lives in Haddenham, Buckinghamshire.

Dawes has the Dawes limit named after him, was responsible for many observations of double stars, knew and worked with William Herschel, and made detailed drawings of the surface of Mars. He received honours from, among others, the Royal Astronomical Society, and has craters named after him on both Mars and the Moon!

Adrian expounded on a number of ideas around why the Hubble Constant may not actually be constant. Galaxies move away from us, and the light is Doppler shifted; when you look at the spectra from the light they emit, it is redshifted. We can measure this, as objects moving away have their hydrogen spectral lines shifted towards longer wavelengths. This has been observed in both nearby and distant objects. It’s this consistent measurement that gives us the Hubble Constant value of 73.8 km/s/Mpc.

However, recent work done by satellites like WMAP and Planck, using measurements of the Cosmic Microwave Background, has come up with a different constant - around 67.0 km/s/Mpc. Adrian spoke about the so-called “Hubble Tension” and outlined a number of possible reasons why this might be, including that our understanding of General Relativity may be incomplete, or that the constant may vary over time. So, watch this space!

Thanks to all our speakers for clear, concise, and enjoyable talks.

If you would be interested in giving a short talk, I would love to hear from you - please email the usual address.