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People saw the sun rise higher in the sky during the summer than in winter. They counted the days that passed from(1)_____ until it returned to that position. They counted three hundred sixty-five days. We now know that is the time Earth takes to move once around the sun. We call this period of time a year.
Early humans also noted changes in the moon. As it(2)_____the night sky, they must have wondered. Why did it look different every night? Why did it disappear? Where did it go?
Even before they learned the answers to these questions, they developed a way to use the changing faces of the moon to tell time.
The moon was "full" when its face was (3)__________. The early humans counted the number of times the sun appeared between full moons. They learned that this number always remained the same -- about twenty-nine suns. Twenty-nine suns (4)_________ We now know this period of time as one month.
发表于 2010-1-23 11:10
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