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* The James Webb Space Telescope[4] will have 18 hexagonal beryllium sections for its mirrors. Because JWST will face a temperature of −240 degrees Celsius (30 kelvins), the mirror is made of beryllium, a material capable of handling extreme cold better than glass. Beryllium contracts and deforms less than glass — and thus remains more uniform — in such temperatures. For the same reason, the optics of the Spitzer Space Telescope are entirely built of beryllium.
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