Teachers who watched the first episode of Carl Sagan's Cosmos show on the Public Broadcasting System may have been impressed by his use of the "Cosmic Calendar" to dramatically introduce the evolutionary time scale of the universe. In this calendar, which Sagan first represented in The Dragons of Eden, the 15 billion year history of the universe is compressed into a single year. Each month represents 1.25 billion years, each day 40 billion years, and each second 500 years. At this scale the entire recorded history of mankind flashes by during the final 10 seconds of the cosmic year. [excerpt]
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Marschall, Laurence. (1981) A Cosmic Clock in the Classroom. The Physics Teacher 19: 185. DOI: 10.1119/1.2340742
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