凯撒大帝和闰日
(原标题: Julius Caesar and Leap Days)
2024-02-29
浏览次数: 15
公元前46年，凯撒大帝改革了历法。根据亚历山大天文学家索西涅斯的建议，儒略历每四年增加一个闰日，以解释地球上的一年略多于365天的事实。用现代术语来说，行星绕太阳公转一周所需的时间是365.24219个平均太阳日。因此，如果日历年恰好有365天，那么它们将每四年偏离地球一年大约一天，最终七月（以朱利叶斯·凯撒本人命名）将出现在北半球的冬季。通过采用闰年，每四年多一天，儒略历年的漂移就会少得多。1582年，教皇格列高利十三世进行了进一步的微调，规定闰日不应出现在以00结尾的年份，除非能被400整除。这种公历系统是目前广泛使用的。当然，地月系统中的潮汐摩擦减缓了地球的自转，并逐渐使一天的时间每世纪延长约1.4毫秒。这意味着大约400万年后，像今天这样的闰日将不再是必要的。这是一枚迪纳留斯银币，上面刻有凯撒大帝（左）和爱神维纳斯的图案。
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In 46 BC Julius Caesar reformed the calendar system. Based on advice by astronomer Sosigenes of Alexandria, the Julian calendar included one leap day every four years to account for the fact that an Earth year is slightly more than 365 days long. In modern terms, the time it takes for the planet to orbit the Sun once is 365.24219 mean solar days. So if calendar years contained exactly 365 days they would drift from the Earth's year by about 1 day every 4 years and eventually July (named for Julius Caesar himself) would occur during the northern hemisphere winter. By adopting a leap year with an extra day every four years, the Julian calendar year would drift much less. In 1582 Pope Gregory XIII provided the further fine-tuning that leap days should not occur in years ending in 00, unless divisible by 400. This Gregorian Calendar system is the one in wide use today. Of course, tidal friction in the Earth-Moon system slows Earth's rotation and gradually lengthens the day by about 1.4 milliseconds per century. That means that leap days like today will not be necessary, about 4 million years from now. This Roman silver coin, a denarius, depicts Julius Caesar (left) and Venus, Roman goddess of love.