Astronomy Picture of the Day——秋分：冬至到夏至的太阳

Equinox: The Sun from Solstice to Solstice 
Image Credit & Copyright: Tunç Tezel

Explanation: Today is an equinox, a date when day and night are equal. Tomorrow, and every day until the next equinox, the night will be longer than the day in Earth's northern hemisphere, and the day will be longer than the night in Earth's southern hemisphere. An equinox occurs midway between the two solstices, when the days and nights are the least equal. The featured picture is a composite of hourly images taken of the Sun above Bursa, Turkey on key days from solstice to equinox to solstice. The bottom Sun band was taken during the north's winter solstice in 2007 December, when the Sun could not rise very high in the sky nor stay above the horizon very long. This lack of Sun caused winter. The top Sun band was taken during the northern summer solstice in 2008 June, when the Sun rose highest in the sky and stayed above the horizon for more than 12 hours. This abundance of Sun caused summer. The middle band was taken during an equinox in 2008 March, but it is the same sun band that Earthlings see today, the day of the most recent equinox.

秋分：冬至到夏至的太阳

今天是秋分，是昼夜等长的一天。从明天开始，一直到2020年的春分，北半球的夜晚将比白天更长，而南半球的白天则比夜晚更长。秋分的时间在夏至和冬至之间，在夏至和冬至，白昼和夜晚的时长相差最大。这幅特征图像是由每小时拍摄一次的多张照片结合而成，呈现出从冬至到春分、夏至的一些关键日子里，土耳其布尔萨上空的太阳轨迹。在这幅图像中，底部的太阳轨迹拍摄于2007年12月的北半球冬至，当时太阳并没有高悬在天空上空，也没有长时间停留在地平线之上。由于缺少光照，于是有了冬天。上方的太阳轨迹拍摄于2008年6月的北半球夏至，当时太阳高悬在天空中，并在地平线以上停留了超过12小时。由于阳光充足，也就有了夏天。中间的太阳轨迹拍摄于2008年3月的春分，为什么没有秋分的太阳轨迹呢，因为地球居民在秋分所看到的太阳轨迹和春分是相同的。

高清原图地址：

https://apod.nasa.gov/apod/image/1909/seasons_tezel_1080.jpg

近期文章：

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NASA

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