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The story was about people living on another planet (for whatever reason) that was always dark and cold except for one day every 100+ years or so when the sun shone on the planet for only a few hours. It focused specifically on a classroom of children. As the teacher and children prepared to go outside to experience sunlight for the only time in their lives one child was accidentally(?) locked in a closet (broom or cloak) and was left behind. The story told of how everyone had fun outside in the sun, being able to take off their coats and feel the warmth of sunlight, except that one child, who was found crying in the closet when everyone came back inside after it became dark again. This story could also be part of a longer story, I don't know.