This hymn is sung at the end of Matins (Orthros) prior to the start of the Divine Liturgy on Sundays and Feast Days when there is a vigil. The western churches have a similar and more condensed version of this hymn.
This is in Plagal of Tone 2 (also called Tone 6) and is the most middle eastern sounding of all of the tones in Byzantine chant. It is one of the most fun, most difficult and most foreign sounding especially to western ears. Enjoy.
By the way, the picture in the corner is that of my godfather, Fr. Aaron (David) Warwick, a priest of the Holy Orthodox Church serving the Liturgy on the day he was ordained. Standing beside him is our master, Bishop BASIL and to the right is my confessor, Fr. Don (Nektarios) Hock. Evlogison, pater!