A representation of the starry heavens, imagined as projected on to a sphere from the center of the Earth and viewed from outside the sphere. Some form of celestial globe must have been constructed by the Greeks, but the earliest surviving example is the Farnese globe of marble dating from the 2nd or 3rd century BC, now in the Museo Nazionale in Naples. It is almost entirely decorative and of little use for measurement. Small Islamic bronze globes of the 11th and 12th centuries survive, but it was not until the 16th century that an interest in them developed in Europe; they were then made of gilded copper or painted wood. An outstanding example, was made in Vienna by Hans Dorn under the supervision of Martin Bylica; it is dated 1480. The magnitudes of the stars are shown by the number of rays radiating from each. A further fine example, of painted wood is signed and dated Johann Stoffler, 1493. One of the functions of the great water clocks of China of the 10th and 11th centuries was to drive a celestial globe, and clock-driven globes appeared in Europe during the Renaissance.