Yorkshire Philosophical Society

Event Information

How to read a stellar barcode
Dr David Jenkins, Department of Physics, The University of York

When light from a star like our sun is split into the spectrum of colours which make it up, dark lines are seen over the top of the rainbow of colours. These dark lines are due to absorption by different chemical elements in the star. An analogy can be made with barcodes which tell you the price and other details of a product in a shop. The stellar barcode tells you how hot the star is and how massive it is, as well as what stage in its lifecycle it is at. Astronomers use these stellar barcodes to work out the distance of stars and it is one of the key ways we know how large our galaxy actually is.

Report
by Carole Smith

When Newton split white light into the colours of the rainbow he demonstrated only the visible part of the spectrum of light, which actually extends in opposite directions into invisible wavelengths – with radio at one end, and gamma rays at the other. Spectroscopy has proved a remarkable tool in physics. Splitting the light of individual stars produces a rainbow barred with Fraunhofer lines at wavelengths where different elements absorb or emit light.  Analysed, these can reveal chemical composition, temperature, turbulence, rotation, and distance. The Hertzsprung-Russell diagram of relative stellar temperatures and luminosity shows that most stars burn hydrogen to make helium. It also enables cosmologists to plot their distance from Earth and, from that, the scale of the universe and its speed of expansion. This complex subject was admirably explained and colourfully demonstrated by a speaker who made it seem so simple.