儒略日
專門名詞
儒略日起點(diǎn)
儒略日的起點(diǎn)訂在西元前4713年(天文學(xué)上記為 -4712年)1月1日格林威治時間平午(世界時12:00),即JD 0指定為UT時間B.C.4713年1月1日12:00到UC時間B.C.4713年1月2日12:00的24小時。每一天賦予了一個唯一的數(shù)字,順數(shù)而下,如:1996年1月1日12:00:00的儒略日是2450084。這個日期是考慮了太陽、月亮的軌道運(yùn)行周期,以及當(dāng)時收稅的間隔而訂出來的。Joseph Scaliger定義儒略周期為7980年,是因28、19、15的最小公倍數(shù)為28×19×15=7980。其中:
28年為一太陽周期(solar cycle),經(jīng)過一太陽周期,則星期的日序與月的日序會重復(fù)。
19年為一太陰周期,或稱默冬章(Metonic cycle),因235朔望月=19回歸年,經(jīng)過一太陰周期則陰歷月年的日序重復(fù)。
15年為一小紀(jì)(indiction cycle),此為羅馬皇帝君士坦丁一世所頒,每15年評定財(cái)產(chǎn)價值以供課稅,成為古羅馬用的一個紀(jì)元單位,
故以7980年為一儒略周期,而所選的起點(diǎn)公元前4713年,則是這三個循環(huán)周期同時開始的最近年份。
由于儒略日數(shù)字位數(shù)太多,國際天文合會于1973年采用簡化儒略日(MJD),其定義為MJD = JD - 2400000.5。MJD相應(yīng)的起點(diǎn)是1858年11月17日世界時0時。
換算
公歷轉(zhuǎn)儒略日
a = ? 14 ? ? --> m o n t h 12 ? y = y e a r + 4800 ? ? --> a m = m o n t h + 12 a ? ? --> 3 {\displaystyle {\begin{matrix}a&=&\left\lfloor {\frac {14-month}{12}}\right\rfloor \\\\y&=&year+4800-a\\\\m&=&month+12a-3\\\end{matrix}}}
適用于格里歷日期(中午):
J D N = d a y + ? 153 m + 2 5 ? + 365 y + ? y 4 ? ? ? --> ? y 100 ? + ? y 400 ? ? ? --> 32045 {\displaystyle {\begin{matrix}JDN&=&day+\left\lfloor {\frac {153m+2}{5}}\right\rfloor +365y+\left\lfloor {\frac {y}{4}}\right\rfloor -\left\lfloor {\frac {y}{100}}\right\rfloor +\left\lfloor {\frac {y}{400}}\right\rfloor -32045\end{matrix}}}
適用于儒略歷日期(中午):
J D N = d a y + ? 153 m + 2 5 ? + 365 y + ? y 4 ? ? ? --> 32083 {\displaystyle {\begin{matrix}JDN&=&day+\left\lfloor {\frac {153m+2}{5}}\right\rfloor +365y+\left\lfloor {\frac {y}{4}}\right\rfloor -32083\end{matrix}}}
儒略日轉(zhuǎn)公歷
相關(guān)條目
儒略歷- 是索西琴修改羅馬歷后的新歷,為格里歷的前身,與儒略日是完全不同的概念。
參考資料
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