Weather Eye (Paul Simons) in The Times has been writing about purple haze glowing in the twilight sky just after sunset. Not auroral though in spite of the colour but the result of volcanic eruptions during the summer months this year. Volcanoes are common occurrences but plumes of sulphurous gas rarely reach the stratosphere. This year two volcanoes have led to just that. The Railkoke volcano in the Kuril Islands in Russia's far east and the Ulawen volcanoe which blew in Papua New Guinea in August. A thin veil of acid and dust from these two eruptions gradually spread over the northern hemisphere, scattering blue light (which at sunset mixes with the red of the setting sun to creat purple colours).
This curious aspect of volcanoes has captured artists over the centuries. For example, Turner's pictures of vivid sunsets that followed big eruptions in his lifetime.