They come from the Liturgy of the Hours, ie the official set of prayers "marking the hours of each day and sanctifying the day with prayer" - otherwise known as the Prayer of the Church and found in the Roman Breviary.
Traditionally one of them is sung at the end of Night Prayer (aka Compline) each day, and each one corresponds to a particular liturgical season.
But they may also be used at other times of prayer when a hymn about Mary is appropriate - particularly among groups of people who do not meet for Night Prayer.
|Anthem:||Season of the liturgical year when it is used:|
|Alma Redemptoris Mater||From the First Sunday of Advent until the close of the Christmas season on 2 February (Candlemas / Presentation of Jesus in the Temple).|
|Ave Regina Caelorum||From 3 February (ie after Candlemas) until the Easter Vigil.|
|Regina Caeli||From Easter Eve until Pentecost Sunday.|
|Salve Regina||From after Pentecost Sunday until the end of the liturgical year.|