__is known to everybody,the moon travels around the earth once erver month,为什么不能用it呢?it 做形式主语,后边是真正得主语

如果用it做形式主语,后面的句子做真正的主语,那么逗号要去掉,添上一个that.
It is known to everybody that the moon travels around the earth once a month.因为此句有逗号隔开,所以前面用as短语.

不可以 如果用it 这就是两句话了。不能加逗号
as is known to everyboby,是一个短语

as is known to everyboby 意思是：众所周知的；=it is well-know
如果用it 做形式主语的话,句子应该改为：
it is known to the moon travels around the earth once erver month.