This hymn is taken from Claudio Monteverdi's exquisite collection of works for the 1610 Vespers of the Blessed Virgin service.
These were originally composed for the court of Mantua, where he served the wealthy Gonzaga family for years.
Tension arose, however, when the Gonzagas came to suspect that Monteverdi may have used the Vespers to try and secure a better job at the Vatican.
Eventually Monteverdi found another, even more prestigious job at the cathedral of St. Mark's in Venice and left Mantua, taking his Vespers with him.
The hymn we just heard sets the text of a ninth-century hymn whose title translates to "Hail, Star of the Sea."
It is addressed to the Virgin Mary, who medieval tradition held to be the patroness of sailors.
The title stuck, and became part of the large repertoire of commonly-set "Marian" texts.