這是我的英文課本的其中一段話

Today,the governments of serveral countries try to locate
NEAs(near-Earth asteroids).  Universit and amateur astronomers
also watch out for dangerous asteroids.  However,there are problems.
First,most asteroids are small and dark. That makes then difficult
to spot. Second,if an asteroids is coming from the direction of
the sun,it cannot be seen because the sun is too bright.
Finally,thereis no large-scale program in the southern hemispthere
to try to find asteroids.

中間說的又黑又小所以不好找這還理解
不過後來說的”從太陽來的asteroids命中南半球的機率比北半球小”
這就不太清楚了
是因為南半球的面積比較少這樣而以嗎？
還是還包含地球傾斜的角度、形狀(橢圓形)...等
或者還有其他理由呢？

請內行解答，謝謝！

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