« IAM LUCIS ORTO SIDERE ». - A hymn sung at the beginning of the Hour of Prime, composed by an unknown author of the school of s. Ambrogio, and therefore called Ambrosian. Indeed, s. Benedetto says in his Rule: « inde sequitur ambrosianum » (chap. 12).
At the dawn of the new day, when the darkness of night has been dispelled, the prayer of the faithful rises to God, imploring aid
for the fulfilment of the day’s duties and for the avoidance of those faults that bring such grave harm to the life of the spirit. The Grace of the Lord will indeed be man’s salvation; through it good works will be accomplished, and by it thoughts and works will be directed to God.
BIBL.: G. B. Belli, Gli inni del Breviario tradotti, Roma 1856, pp. 15-25; S. Baumer, Histoire du Bréviaire romain, I, Parigi 1905, p. 367 sg.; F. Vanderstuyf, Les hymnes de l'Ordinaire du Bréviaire romain, ivi 1922, pp. 36-37; A. Mirra, Gli inni del Breviario romano, Napoli 1947, pp. 45-46. Silverio Mattei