Question: What is the structure of our services? AT
Answer: The Structure of Services.
The Ecclesiastical Day.
The ecclesiastical day begins, not at midnight, but at sunset. The time from one sunset to the next is occupied by an orderly succession of Service which collectively are called the Daily Cycle: Vespers, Aftersupper ( Apodiepnon), Mesanyctiko, Orthros, First Hour, Third Hour, Sixth Hour, Typica, and Ninth Hour. The Liturgy ordinarily comes after the Sixth Hour.
Each Service in the Daily Cycle, as performed, is a fusion of two elements: a permanent framework which is characteristic of the Service, and materials proper to the particular occasion which are built into that permanent and characteristic framework.
The permanent framework of a Service is called the Acolouthia of that Service.
The sources from which inserted material is taken are called Sequences.
Each Sequence supplies for all the Acolouthies of the Daily Cycle the material required for a particular Remembrance — that is to say, the material proper to a particular day of the week, or proper to a particular date of the month, or proper to a particular day in the Seasons immediately before and after Pascha. For example, on a Sunday dated December 6, each Acolouthia of the Daily Cycle must build into its framework its portion of the Resurrectional Sequence of the current Tone, because all Sundays are Remembrances of Pascha; and must also incorporate the material appointed for it in honor of St. Nicholas, the Saint of the day, which material is the Sequence for that December date. These Sequences, that of the Resurrectionals of the current Tone and that of December 6, exhibit their material in the order in which it must be used: that is to say, in the order of the Acolouths which compose the Daily Cycle, beginning with the "Lord, I call upon Thee" (Kekragarion) at Vespers, the first place in the permanent and characteristic framework of Vespers and therefore also the first place in the succession of the Acolouthia of the Daily Cycle where material proper to the day and date must be inserted.