Day, night, and seasons .
白天、夜晚和季节。
Earth axis is an imaginary line that goes through it.
地轴是一条穿过它的假想线。
Earth rotates around its axis once in 24 hours.
地球每24小时绕地轴自转一次。
Half of Earth always faces the sun.
地球的一半总是面向太阳。
There it is the day.
就是这一天。
There is light.
有光。
The other half of Earth does not face the sun.
地球的另一半不面向太阳。
There it is the night.
这就是夜晚。
There is darkness.
有黑暗。
Sunrise is when the sun first appears in the sky.
日出是太阳第一次出现在天空中。
It is the start of day.
这是一天的开始。
Sunset is when the sun disappears from the sky.
日落是指太阳从天空中消失。
It is the start of night.
这是夜晚的开始。
The rotating Earth causes night and day.
旋转的地球导致黑夜和白昼。
The Earth's axis is tilted.
地轴是倾斜的。
Part of Earth tilts toward the sun.
地球的一部分向太阳倾斜。
It gets more sunlight and it is warmer than the other part.
它得到更多的阳光，比其他部分温暖。
Earth orbits the sun in one year.
地球绕太阳公转一年。
The part of Earth that tilts toward the sun slowly changes.
地球向太阳倾斜的部分缓慢变化。
This is why the seasons change.
这就是季节变化的原因。