The speech is proceeding rather smoothly and, I think, kind of explicably as the Lady defends the sun-clad power of chastity.

我认为演说进行的相当顺利，当女士维护贞节如太阳一般的力量时，听上去是可解释的。

耶鲁公开课 - 弥尔顿课程节选

Maybe it could refer to either the poet or the sun throughout the entire line, if you think of the mantle blue as being the actual sky that the sun is able to twitch over his shoulder.

或者两者皆可,从整句的行文看来，如果你们把蓝色的丝巾看作是真实的天空的话,那么太阳的确是能够在他的肩上轻轻颤动。

耶鲁公开课 - 弥尔顿课程节选