APOD251221 自转地球上的至日

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自转地球上的至日

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http://apod.nasa.gov/apod/image/2512/SeasonsSpinningEarth_Meteosat9.mp4

图像提供: Meteosat 9[1], NASA[2], Earth Observatory[3], Robert Simmon[4]

英文原文:Explanation: Can you tell that today is a solstice by the tilt of the Earth? Yes. At a solstice, the Earth's terminator -- the dividing line between night and day -- is tilted the most. The featured time-lapse video demonstrates this by displaying an entire year on planet Earth in twelve seconds. From geosynchronous orbit , the Meteosat 9 satellite recorded infrared images of the Earth every day at the same local time . The video started at the September 2010 equinox with the terminator line being vertical: an equinox. As the Earth revolved around the Sun, the terminator was seen to tilt in a way that provides less daily sunlight to the northern hemisphere, causing winter in the north. At the most tilt , winter solstice occurred in the north , and summer solstice in the south. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way , causing winter in the southern hemisphere -- and summer in the north. The captured year ends again with the September equinox , concluding another of billions of trips the Earth has taken -- and will take -- around the Sun. APOD Review: RJN's Night Sky Network Lecture 说明：你能从地球的倾斜角度判断今天是冬至吗？是的。在至日时，地球的晨昏线[5]-即昼夜分界线-倾斜角度最大。这段缩时视频[6]展示了这一现象，视频在短短十二秒内呈现了地球[7]一整年的变化。从地球同步轨道[8]上，Meteosat 9[9]卫星每天在相同的当地时间[10]记录下红外线[11]图像。视频从2010年9月[12]的秋分开始，此时晨昏线垂直，即秋分点。随着地球[13]绕太阳公转，晨昏线的倾斜使北半球每天接受到的阳光减少，造成北半球的冬季[14]。在最大倾斜[15]时，北半球迎来冬至，而南半球则是夏至[16]。随着时间推移，2011年3月[17]的春分出现在视频播放到一半时，随后晨昏线向另一侧倾斜[18]，导致南半球进入冬季[19]，而北半球则是夏季。这段记录的年份再次以9月的秋分[20]结束，完成了地球绕太阳的又一次旅程，这只是地球数十亿次（并将持续数十亿次）旅程中的一次。