Next at The Crypt is Starfield, an exhibition of painted star maps across the milky way.
"The painted starmaps represent the stars coloured according to their spectral class in the OBAFGKM system published by Annie Jump Cannon in 1901. Spectral class is based on an analysis of the absorption and emission lines created by gases in the star's atmosphere and revealed when the light from an individual star is focused through a prism. It is a good indication of the temperature and predominant colour of radiated light. In very hot B and O types (10,000°K to 60,000°K) the spectrum is weighted in favour of ultra-violet and blue and with little radiation in the red. In cool M and K types (2,700°K to 5,200°K) the spectrum is loaded at the red end with little radiation in the blue. From G to A (5,400°K to 9,900°K) there is significant radiation across the whole visible spectrum and while the measured radiation peaks in this or that part of the spectrum, any perceived colour can depend on colour contrast effects with neighbouring stars.
Under a dark sky only a handful of the brightest stars appear coloured to the naked eye. Vision at night is mostly done by monochrome seeing rod cells, light and dark. At full stretch, night vision, they are about 16 times more sensitive to light than the colour seeing cone cells. It needs a bright source of light for the perception of colour and, in naked eye seeing, most stars are too faint to crossthe threshold of light into colour. The easiest stars to see coloured are very bright stars towards the red end of the spectrum, Betelgeuse, Arcturus, Antares.
Stars appear in clumps of interstellar gas that coalesce into a clusters of stars, of which the Pleaides star cluster is a famous example. These groupings are held together by gravity attraction but drift apart. When stars are coloured up on maps according to spectral class some number of the colour groupings are real, genuine families of stars born together, while other groupings are assembled by chance. The scatter patterns remind me of wild flowers."
- John Cox
16th — 22nd August
Friday 16th, 11 — 4pm
Saturday 17th, 11 — 4.30pm
Monday 19th - Wednesday 21st, 11 — 4pm
Thursday 22nd 11 — 1pm
Closed Sundays. Free admission.
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