I have an interesting follow-up comment to add to this question. The book of Jude refers to prophesies of Enoch that are not found in our modern Bible. Jude is actually referring to verses in the Book of Enoch, which was very popular among early Christians, but was excluded from the New Testament canon by those who translated our modern version. Among other things, the Book of Enoch tells the story of how angels mated with human women and bore giant children. If Enoch's account was true, it gives further clarity to Paul's comment about women covering their heads 'because of the angels' and Peter's account of angels who 'left their first estate' and are now 'reserved unto judgment.'