Sentence:  Know none before us, self-begot, self-rais'd / By our own quick'ning power, when fatal course / Had circl'd his full <WSD>Orbe</WSD>, the birth mature / Of this our native Heav'n, Ethereal Sons. 
Meaning of the word marked with <WSD> tags:  A period of time marked off by the revolution of a heavenly body.