[填空题]
A science-fiction tale describes an artificial "planet" in the form of yft al6j0/54sif cm q.a bandcyi r23( la+y)d o r:6jpm(ndl completely encircling a sun (Fig. 5-40). The inhabitants live on the inside surface (where it is always noon). Imagine that ta jio yd2 n 3mr:pl(d+cr(6y)lhis sun is exactly like our own, that the distance to the band is the same as the Earth-Sun distance (to make the climate temperate), and that the ring rotates quickly enough to produce an apparent gravity of g as on Earth. What will be the period of revolution, this planet's year, in Earth days?
