Dame Carole Jordan, who has died aged 84, was internationally renowned for her studies of the outer atmosphere of the sun and other cool stars. In 1994 she was appointed the first female president of the Royal Astronomical Society and she was a formidable advocate for women in science.
When we glance at the sun we see a yellow zone at a temperature of 5,500C – the photosphere. When the light is spread out into all its wavelengths, myriad bright and dark lines appear, corresponding to electrons being emitted and absorbed by different atoms. The strongest lines in the visible spectrum come from a thin layer just above the visible surface, the chromosphere. Above this lies the corona, which extends for millions of kilometres and only becomes visible during eclipses. In this zone the temperature increases to 1 million degrees, and so the light and spectral lines mainly become visible at extreme ultraviolet (EUV) or soft X-ray wavelengths.
