同样是这一天，站在南极点上的人也会看到太阳匆匆学过地平线，这便是长达六个月的极昼的开始。
On the same day, a person at the South Pole would also see the sun skim the horizon, beginning six months of uninterrupted daylight.
在北半球的秋分日那天，站在北极点上的人会看到太阳匆匆掠过地平线，这也预示着长达六个月的极夜的开始。
On the Northern Hemisphere's autumnal equinox day, a person at the North Pole would see the sun skimming across the horizon, signaling the start of six months of darkness.
这个平行线是一个有半径的圆，这个半径是小于a的，因为如果这个环越靠近北极点，它的半径实际上会越来越小。
So now, this parallel as a circle of radius, well, the radius is less than a because if your vertical is to the North Pole, it will be actually much smaller.
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