恩,有却别,第二个句子是病句,which 不能直接加在那里.
想要加也得加 which is,如果单单加个 which 那就要出语法错误了.
① They based their calenders on the natural cycles:the solar day,marked by the successive periods of light and darkness as the earth rotates on its axis.
② They based their calenders on the natural cycles:the solar day,which is marked by the successive periods of light and darkness as the earth rotates on its axis.
加了个 which is,现在两个句子的意思就完全相同了.
一模一样的,只是表达的方法稍微有一点点不同而已、