Quite right, Dexter Sinister, it was a lone planet circling six stars. As a result, the inhabitants are never in the darkness, they are not used to darkness. Then when once every 2000 years the night falls, it leads to anarchy and the end of civilization.
One of the best stories Asimov ever wrote. I remember, I particularly liked the idea of the amusement park ride. The ride consisted of riding three minutes in complete darkness. For people who have never been exposed to darkness, that must have been quite scary, probably comparable to the scariest of the roller coaster rides.
Asimov ended the story when the night came on and anarchy started. However, later he wrote Nightfall the novel (with somebody else). Here he continued the story even after the start of anarchy, all the way upto the dawn of the new civilization.
