每逢十二月，当黑夜笼罩在北极上空，南极洲就开始享受着极昼的阳光。
Each December, while darkness engulfs the arctic, Antarctica enjoys round-the-clock sunlight.
解说： 在这张来自卡西尼飞行器的戏剧性的图片中，土星的卫星之一的土卫二在阳光的照射下显出一道月牙，阴森地逼近了土星黑夜侧的上方。
Explanation: A sunlit crescent of Saturn's moon Enceladus looms above the night side of Saturn in this dramatic image from the Cassini spacecraft.
这条黑夜与白天分界线的形状随着季节的变化面变化，它代表着不同的白天时间长度和不同的阳光照射量。
The shape of this line between night and day varies with the seasons, which means different lengths of days and differing amounts of warming sunshine.
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