Nocturns

Nocturns is the name for the canonical hours devoted to nighttime prayer. While the evolution of the canonical hours is a bit confusing, it appears that Nocturns, or nighttime prayer was practiced primarily in monasteries, and so was joined with the more established Matins (or Lauds)—morning prayer—which was practiced throughout Christendom. Today, the term refers to the four prayers said in the night: Vespers, or evening prayer; Compline, or the prayer before sleep; Midnight Office, which in modern practice occurs just before Matins, was generally a private practice, which often consisted of reciting Psalm 118. A completely different Nocturn is the Vigil, which has come to refer to an entire night spent in prayer—a special event, often preceding a feast day. Traditionally, the division of Matins into three nocturns was seen as replicating the three nighttime watches, or vigils, of the guards who stood watch as the early Christians met at night to avoid persecution.

In practice, what I am talking about then as the start of the day, is the remnant of that Midnight Office. It is an invitatory meditation, a preparation for the day which will follow. It is a meditation marked by penitence and hope.

While this Invitatory Prayer varies among the various Orthodox and Catholic practices, and varies according to the day of the week and the special feast days. In its simplest, weekday form, the office consists of reading Psalm 118, the longest Psalm in the Vulgate, and the chanting of the Troparia of the Bridegroom, or the Bridegroom’s Prayer, derived from Matthew 25:6 (KJV):
"And at midnight there was a cry made, Behold, the bridegroom cometh; go ye out to meet him."