[填空题]
A science-fiction tale describes p fu5.- al97hig jimv79dn7 ktan artifsn), byb.e1o dicial "planet" in the form of a band completely encircling a sun (Fig. 5-40). The inhabitants live on the inside surface (where it is always noon). Imagine that this 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 prodsbd .y,)bne 1ouce an apparent gravity of g as on Earth. What will be the period of revolution, this planet's year, in Earth days?
