On the eve of the the feast of the Epiphany ….Epiphany (“manifestation”, “striking appearance”) or Theophany (Ancient Greek (ἡ) Θεοφάνεια, Τheophaneia meaning “vision of God”), which traditionally falls on January 6, is a Christian feast day that celebrates the revelation of God the Son as a human being in Jesus Christ. Western Christians commemorate principally (but not solely) the visit of the Magi to the Baby Jesus, and thus Jesus’ physical manifestation to the Gentiles. Eastern Christians commemorate the baptism of Jesus in the Jordan River, seen as his manifestation to the world as the Son of God.
Eastern Churches following the Julian Calendar observe the Theophany feast on what for most countries is January 19 because of the 13-day difference today between that calendar and the generally used Gregorian calendar.
The observance had its origins in the Eastern Christian Churches and was a general celebration of the manifestation of the Incarnation of Jesus Christ. It included the commemoration of his birth; the visit of the Magi to Bethlehem; all of Jesus’ childhood events, up to and including his baptism in the Jordan by John the Baptist; and even the miracle at the wedding at Cana in Galilee. It seems fairly clear that the Baptism was the primary event being commemorated.
Since 1970, the rule for the Roman Rite of the Catholic Church is: “The Epiphany of the Lord is celebrated on 6 January, unless, where it is not observed as a Holy day of obligation, it has been assigned to the Sunday occurring between 2 and 8 January.”
In the Church of England, the feast is celebrated on the Twelfth Night (holiday), the Twelfth Day being January 6. The Monday after Epiphany is known as Plough Monday
A separate celebration of the Baptism of the Lord was introduced for Latin Rite Roman Catholics in 1955. Initially, this was to be held on January 13, the then octave day of the Epiphany, but in the 1969 revision of the General Roman Calendar the date was changed to the first Sunday after January 6. In countries where in a particular year the Epiphany falls on January 7 or 8, the feast of the Baptism of the Lord is celebrated on the following Monday. In the Church of England, the same custom may be followed. In the Episcopal Church in the United States, the feast of the Baptism of the Lord is always the Sunday after January 6.
https://hrexach.wordpress.com/2014/01/05/on-the-eve-of-the-the-feast-of-the-epiphany/