Mirror, Mirror; on the Truss Structure. The first six mirrors of the James Webb Space telescope are about to begin their final cryogenic testing… …moving the powerful new instrument one step loser to its goal of taking baby pictures of infant galaxies near the beginning of the Universe. Each hexagonal mirror is 1.5 meters – just under five feet – across. 18 such mirrors are being arrayed together to function as one extremely large primary mirror, 6.5-meters – that’s a little over 21 feet– in diameter. They’re cast of beryllium, a lightweight but stiff metal, which won’t lose its shape in the very cold temperatures of deep space, far from Earth, where the telescope will fly. But, by itself, beryllium does not reflect the near-infrared light required by the Webb Telescope very efficiently… … so each mirror segment’s surface has been painted with a little more than a tenth of an ounce of molten gold, to form a coating that’s 200 times thinner than a human hair. Cryo-testing of the mirrors is a milestone. But the James Webb Telescope is far over-budget. And it has taken 8 years for these mirrors to be built. For SPACE.com, I’m Dave Brody