It was only at two points in the year that the night and the day were of equal length and that was at the spring or fall equinox.
一年之中只有两次，白天和夜晚的长度一样，即春分和秋分。
Day and night would each be exactly 12 hours long on a spring or fall equinox only if the sun were a single point of light and Earth had no atmosphere.
如果想要昼夜在春秋分日达到精确地12小时等长，除非太阳是个单点光源或者地球上没有大气层。
Day and night would each be exactly 12 hours long on a spring or fall equinox only if the sun were a single point of light and Earth had no atmosphere.
如果想要昼夜在春秋分日达到精确地12小时等长，除非太阳是个单点光源或者地球上没有大气层。
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