"Eala Earendil engla beorhtast
ofer middangeard monnum sended"
"Hail Earendil, brightest of the angels,
over Middle Earth sent unto man"
This is an extract from a cycle of religious poems in the alliterative form, attributed to Cynewulf, an Anglo-Saxon poet of the early 9th century. It appears to refer to the morning star (Venus), but could well also be alluding to John the Baptist, or even to Christ.
The idea of Earendil sailing his boat across the heavens above Middle Earth was to become one of the earliest elements of J. R. R. Tolkien's private mythology, formed while he was still a student. For this, see Humphrey Carpenter's biography of Tolkien, chapter 6; also the "Silmarillion", and the long poem about Earendil in the chapter "Many Meetings" in "The Lord of the Rings". Needless to say, there is no reference to Earendil in the film version!