Somehow I got on the e-newsletter for the Eastern Diocese. This newsletter goes out weekly, and the latest edition announced that the Eastern Diocese's website has all the weekly sharagans (hymns) and other things that change weekly. This is called Giratsooyts.
Not all churches follow these (although all the ones I have gone to in the Eastern Diocese do); my old church sang the same Der Takavoryatz every week. But for those of you who do go to a church that follows these, it can be really helpful to know what you're singing before you walk into church on Sunday morning.