標題: Equinox?? [打印本頁] 作者: dolphin_ice 時間: 21/3/2008 07:45 PM 標題: Equinox?? Given that: 1. Equinox is the day that the daylight length and night length are the same. 2. The date of Easter depends on Equinox
Question: Why is the date of Equinox not affected by attitudes? (apart from Arctic and Antarctica)作者: inthomaspy 時間: 21/3/2008 09:04 PM The date of equinox actually means the date that the places in equatorial region receive overhead sun at 12 noon. As on that day, all the places in equatorial region receives sunlight with an angle of the sun of 90 degree, so no matter how high high the altitude is, it will receive sunlight with an angle of the sun of 90 degree.
[ 本帖最後由 超夢夢的夢境 於 21/3/2008 09:20 PM 編輯 ]作者: dolphin_ice 時間: 21/3/2008 11:31 PM sorry about the typo, I do mean latitude.
Re 超夢夢的夢境, I thought different latitudes have different day and night lengths. The variation is very big. I had been living in England and Hong Kong for many years, I experienced the dramatic difference.
In England, the sun can set after 10 o'clock in the summer, but before 4 o'clock in the winter. Hong Kong does not have such a big difference.作者: 超夢夢的夢境 時間: 22/3/2008 10:44 AM 夏天時,北半球傾向太陽,所以北半球日晝時間長 冬天時,南半球傾向太陽,所以北半球日晝時間短
如果這裡不明白,可以嘗試由比較數學的方法理解 畫一個"赤道與公轉面之間角度" against time 的圖 那個將是一條平滑連續的曲線 而且角度有時候是正數,有時候是負數(南北半球各自都有傾向太陽的時間) 所以有一刻,該角度為零(晝夜平分點) -------------------------------------------------------------------------------------------------------------------------------------- 而且,地球上每一點的angular speed(frequency)都是一樣的(2pi rad per day) 由一點開始,自轉到另一面(pi rad)需要半天