Image: Silicon sphere for Avogadro project

Description: A 1-kg single-crystal silicon sphere for the Avogadro Project is shown above in the hands of Master Optician Achim Leistner at the Australian Centre for Precision Optics (ACPO), which is part of Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). ACPO's spheres are among the roundest man-made objects on Earth. (The gyroscopes of Gravity probe B are equally round but are in orbit, not "on Earth".) If one of their Ø 93.6 mm spheres, which had an out-of-roundness of 35 nm, was scaled to the size of the Earth, its ‘continents’ would gradually rise only 2.4 meters above sea level.
Title: Silicon sphere for Avogadro project
Credit: CSIRO
Author: The Commonwealth Scientific and Industrial Research Organisation of Australia
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