The Oxford Science Lecture Series

DR HELEN MASON

Department of Applied Mathematics and Theoretical Physics, University of Cambridge

"The Dynamic Sun"

University Museum, Oxford, 30th June 1999

The Sun is our nearest star (a mere 150 million km away), and if we are to understand anything about how stars work it is the natural place to start. It has been worshipped since ancient times and still inspires passion today in solar watchers of all ages, from primary school children to research scientists such as Dr Helen Mason.

In her lecture on the Dynamic Sun for Oxford AWiSE and The Oxford Trust, Dr Mason spoke about her enthusiasm for studying the sun. She has worked in solar physics throughout her research career and has been involved in many exciting projects to observe the sun and try to understand its inner workings.

Galileo and Newton both studied the sun as part of their scientific endeavours. Galileo observed sunspots and was able to deduce that the sun (or at least its surface) rotates. Galileo eventually became blind and Newton also damaged his sight and so these two scientists might act as a warning to solar watchers today - never directly observe the sun.

Solar eclipses are of course very topical at the moment, and Dr Mason described her first actual experience of a solar eclipse in the Caribbean last year. It is an eerie experience to see the sun's light disappear in the middle of the day. What is particularly special about seeing a total solar eclipse is that it allows the haze of light surrounding the sun, the sun's corona, to be visible. The corona is always there but as it is about a million times less bright than the light from the surface of the sun we are normally unable to see it. Very curiously, research has shown that the temperature of the corona is in fact much greater than that of the surface of the sun (a million degrees K instead of 6000 degrees K), i.e. the temperature increases above the sun's surface. Much research is being done to try to explain this phenomenon.

Dr Mason spoke about the various space missions she has been involved in to observe the sun, including Skylab in 1974 and the Solar Maximum Mission in 1980. Currently a satellite called SOHO (Solar and Heliospheric Observatory) is providing very interesting new data. It is positioned in an orbit a very long way from the Earth in such a way as to be able to observe the surface of the sun 24 hours a day. It can make measurements of magnetic fields, solar oscillations, the atmosphere and of phenomena such as solar flares and tornadoes on the surface of the sun. It has already caused the solar physicists some heart-stopping moments when it "went missing" last summer for some months - its energy-providing solar panels became oriented away from the sun and it lost power so that it was unable to transmit its position back to earth. Fortunately it was found and brought back into action from the earth.

Dr Mason's talk left us with a much clearer understanding of the problems that solar physics is currently trying to explain, and of what we might be observing if we are able to see the total solar eclipse this August. She finished by telling us about some interesting web sites relating to the sun - both well worth a look!

sohowww.estec.esa.nl -- The SOHO website

www.sunblock99.org.uk -- Young scientists investigate the sun.

Dr. Catherine Hobbs.