2、The first calendar to fix these two days on definite dates of the year was the solar calendar(阳历)， which had 365 days in a year and --- every four years --- a “leap-year(闰年)” with one extra day. To an observer on earth， the sun seems to move farther and farther away from the equator(赤道)to the north until on June 21st it seems to reach its furthest point north.Then it seems to “pause” for one day before it turns around and goes back.Then it goes further and further south until on December 22nd it appears to “pause” again for one day before swerving(改变方向)back north again.These two days are called the Summer Solstice(夏至)and the Winter Solstice(冬至)respectively.