少见！十五的月亮十七圆

今年中秋节期间将出现罕见的"十五的月亮十七圆"现象1。月亮最圆时刻将在9月27日凌晨0时49分出现，即农历八月十七凌晨1。这意味着中秋节当晚（农历八月十五）的月面被照亮部分已超过98%，但真正的满月要到两天后才会到来1。

中国科学院紫金山天文台科普主管王科超解释了这一现象的成因1。由于月球绕地球的轨道为椭圆且运行速度变化，从"朔"到"望"的时间在13.90天到15.61天间变化，因此"望"可能出现在农历十四到十七日1。今年还巧合地与秋分仅差两天，秋分落在农历八月十三，中秋是八月十五1。

This year's Mid-Autumn Festival presents an uncommon celestial occurrence where the full moon reaches its brightest phase on the seventeenth day of the eighth lunar month rather than the traditional fifteenth day.1 The moment of maximum illumination will occur on September 27 at 12:49 AM.1 At this time, the moon will have entered its "full moon" or "wang" phase, marking a notable deviation from the conventional timing typically associated with the Mid-Autumn celebration.1

The scientific explanation for this phenomenon lies in the elliptical nature of the moon's orbit around Earth combined with variations in its orbital speed.1 According to Wang Kechao, the science communication director of the Purple Mountain Observatory under the Chinese Academy of Sciences, the interval between the new moon phase ("shuo") and the full moon phase ("wang") fluctuates between a minimum of 13.90 days and a maximum of 15.61 days.1 This variability means that the full moon can theoretically occur anywhere from the fourteenth to the seventeenth day of the lunar calendar.1 By the night of the Mid-Autumn Festival on the fifteenth day of the eighth lunar month, the illuminated portion of the moon's surface will already exceed 98 percent.1 Adding to the coincidental nature of this year's astronomical alignment, the autumnal equinox falls on the thirteenth day of the eighth lunar month, placing it just two days before the Mid-Autumn Festival.1