数千年前古代民族发现，白天夏季比冬季长，而黑夜夏季比冬季短。他们知道这种现象与季节变化和动植物生长有很大关系。他们通过多少代人辛辛苦苦地观察，确认在北半球十二月二十二日的白天最短，过了那天后，白天就逐渐变长，一直到六月二十一日，那天是一年中的白天最长，黑夜最短的一天。此后，白天又会开始逐渐变短。起初，这两天的具体日子必须每天计算，而且要看所使用的历法的种类而定。
最早把这两天固定在每年一定的日子的年历是阳历，按照这种年历，一年有三百六十五天，每四年有一个“闰年”，多一天。
在地球上的观察者看来，太阳似乎离开赤道一步步向北移动，到六月二十一日，移动到了北面最远的地方，接着太阳似乎“暂停”移动一天，然后就回头移动，一步步向南移动，直到十二月二十二日，太阳似乎又“暂停”一天，再回过头来向北移动，这两天就分别叫做夏至和冬至。

数千年前古代民族发现，白天夏季比冬季长，而黑夜夏季比冬季短。
Thousands years ago, ancestors noticed that day time of summer is longer than the day time of winter, and nights are opposite.
他们知道这种现象与季节变化和动植物生长有很大关系。
They knew this phenomenon have great relation with the variation of seasons and life circle of animals and plants.
他们通过多少代人辛辛苦苦地观察，确认在北半球十二月二十二日的白天最短，过了那天后，白天就逐渐变长，一直到六月二十一日，那天是一年中的白天最长，黑夜最短的一天。
After observation of generations, they concluded that the shortest day time of the Northern Hemisphere happens at every 22nd of December. After that day, day time increases day by day until 21st of June, and that day would have the longest day and shortest night among the whole year.
此后，白天又会开始逐 渐变短。起初，这两天的具体日子必须每天计算，而且要看所使用的历法的种类而定。
Then, the day time will decrease. At the first beginning, people calculated every day to confirm the actual dates of these two days, and the dates vary with the different type of calendar.
最早把这两天固定在每年一定的日子的年历是阳历，按照这种年历，一年有三百六十五天，每四年有一个“闰年”，多一天。
Gregorian calendar firstly fix these two days to particular dates. According to this calendar, there are 365 days in one year, and one leap year comes out from every four years, and one more day is the difference for this leap year.
在地球上的观察者看来，太阳似乎离开赤道一步步向北移动，到六月二十一日，移动到了北面最远的地方，接着太阳似乎“暂停”移动一天，然后就回头移动，一步步向南移动，直到十二月二十二日，太阳似乎又“暂停”一天，再回过头来向北移动，这两天就分别叫做夏至和冬至。
Observing from earth, the solar is moving towards north away from equator until 21st of June, and “pause” for one day, then turns back to south until 22ed of February and “pause” and turns back again. These days are called “the Summer Solstice” and “the Winter Solstice”.