'Inequalities of the Solar Surface', 1875
© Science Museum / Science & Society Picture Library
Illustration taken from 'Le Soleil' (Paris, 1875) by Angelo Secchi( 1818-1878), showing the surface of the Sun. 'On examining the Sun with instruments posesing a large aperture and strong magnification, one sees that its surface, far from being smooth and uniform, has an irregular and undulating appearance, like a stormy sea.' Secchi was a pioneer of solar astronomy in the 19th century. This image depicts what is known as granulation in the photosphere, the visible surface of the Sun. It consists of 'bubbles' of hot gas which rise rapidly to the surface of the photosphere due to convection. Upon arriving, they release their energy by radiation, cool, and sink back into the Sun's interior along the darker borders between the granules.