Jealousy is a central theme in Ray Bradbury's "All Summer in a Day," driving the actions and emotions of the characters. The story is set on Venus, where the sun shines for only one hour every seven years. Margot, a young girl who remembers the sun from her time on Earth, becomes the target of her classmates' envy. Her memories and potential return to Earth spark jealousy among the other children, who have never experienced the sun's warmth and beauty. This jealousy culminates in a cruel act that deprives Margot of witnessing the rare event of sunshine on Venus.

The children's jealousy is rooted in their lack of experience with the sun. Margot's vivid memories of the sun, described as "the way the sun was and the sky was when she was four in Ohio," highlight her unique connection to something the other children cannot remember. Their envy is compounded by the fact that Margot might return to Earth soon, a possibility that represents a future they cannot have. This is expressed in their hatred for her "pale snow face, her waiting silence, her thinness, and her possible future."

The children's jealousy manifests in their disbelief and ridicule of Margot's memories. They accuse her of lying, as seen when a boy says, "Aw, you didn’t write that!" about her poem on the sun. This accusation is a coping mechanism for their inability to understand or accept what they have never known. The children's jealousy and fear of the unknown lead them to lock Margot in a closet, preventing her from seeing the sun. This act of cruelty is a direct result of their envy and their desire to control what they cannot have.

Margot's isolation and the children's subsequent remorse highlight the destructive nature of jealousy. The children realize too late that Margot's descriptions of the sun were true, and their actions have deprived her of a precious moment. This regret underscores the consequences of allowing jealousy to dictate behavior and the importance of empathy and understanding. The story serves as a cautionary tale about the dangers of envy and the need for kindness and acceptance of differences.