The term Octave of Easter may refer either to the eight day period (Octave) from Easter Sunday until the sunday following Easter, inclusive; or it may refer only to that Sunday after Easter, the Octave Day of Easter (sometimes known as Low Sunday). That Sunday is also known historically as St. Thomas Sunday and Quasimodo Sunday. Since 1970 Low Sunday has been officially known as the Second Sunday of Easter (referring to the Easter season) in the Roman Catholic Church. On April 30, 2000, it was also designated as Divine Mercy Sunday by Pope John Paul II.
Among Eastern Christians the day is known as Thomas Sunday.
Octave refers to an eight-day feast or the eighth day following that feast, sometimes referred to as the "Octave Day".
St. Thomas Sunday is so called because the Gospel reading always relates the story of "Doubting Thomas," in which Thomas the Apostle comes to believe in the Resurrection of Jesus only after being told by the resurrected Christ to place his finger in the nail marks and his hand in His side. In the Gospel accounts, this event takes place on the eighth day after the Resurrection, hence their significance for this Sunday ( ).
Divine Mercy Sunday is the culmination of the novena to the Divine Mercy of Jesus, a devotion given to St. Faustina (Mary Faustina Kowalska) and is based upon an entry in her diary stating that anyone who participates in the Mass and receives the sacraments of Confession and the Eucharist on this day is assured by Jesus of full remission of their sins. The devotion was actively promoted by Pope John Paul II, who officially set its commemoration on this Sunday in 2000.
Prior to the 1970 this day was called Low Sunday. It was sometimes said that the name derives from its relative unimportance compared to the solemnities of Easter Day, but it is possible that "low" is a corruption of the Latin word Laudes, the first word of the Sequence of the day: "Laudes Salvatori voce modulemur supplici" (Let us sing praises to the Savior with humble voice). Laudes means "praises".
Traditionally, the newly-baptised would receive baptismal gowns that would be worn until this day, and the official Latin name is Dominica in Albis [Depositis], "Sunday in [Setting Aside the] White Garments". Hence "White" and "Alb" Sunday—which is also the etymology of Whitsunday (Pentecost).
The name Quasimodo came from the Latin text of the traditional Introit for this day, which begins "Quasi modo geniti infantes..." ("As newborn babies...", from the First Epistle of Peter ( ).  Literally, quasi modo means "as if just now".
In the Eastern Orthodox, Coptic Orthodox and certain Eastern Catholic churches, the first Sunday after Pascha (Easter) is known as Thomas Sunday, after the Gospel passage read that day ( ) which recounts the story of Christ appearing to the Apostle Thomas in order to dispel his doubt about the Resurrection. It should be noted that among Eastern Christians Thomas is not so much remembered as "doubting Thomas," but is rather remembered for his confession of faith: "My Lord and my God," thus being the first to publicly proclaim the two natures of Christ: human and divine.
The entire week from Pascha to Thomas Sunday, known as Bright Week or Renewal Week, is considered to be one continuous day. The hymns chanted every day are identical to those chanted on the Sunday of Pascha, with the exception of a few parts that are taken from the Octoechos (the "Book of the Eight Tones"). Each day has a different tone: Easter Sunday is Tone One, Bright Monday is Tone Two, and so on through the eight tones (skipping Tone Seven, the "Grave Tone"). On Bright Friday, in addition to the normal Paschal hymns, special stichera and a canon in honor of the Theotokos (Mother of God) are chanted in commemoration of her Icon of the "Life-giving Spring." During all of Bright Week the Royal Doors on the Iconostasis are kept open—the only time of the year when this occurs. The doors are closed before the Ninth Hour on the eve of Thomas Sunday. However, the Afterfeast of Pascha will continue until the eve of the Ascension.
Thomas Sunday is also called Antipascha (literally, "in the place of Pascha") because those who for honorable reason were not able to attend the Paschal Vigil, may attend services on this day instead. Pascha is a unique feast in the church year; being the "Feast of Feasts" it follows a format unlike any other day. Those liturgical elements normal to a Great Feast of the Lord which were displaced by Pascha's unique elements are instead chanted on Thomas Sunday.
All Sundays of the year are determined by the date of Pascha. Thomas Sunday is the first Sunday of the liturgical year that takes its character and naming from the current Pascha (all earlier Sundays having depended on the previous Pascha).
The days following Thomas Sunday are traditional days for visiting the cemeteries to greet departed loved ones with the joyous good news of the Resurrection. In Russia this normally takes place on the Tuesday following Thomas Sunday and is called Radonitsa ("Day of Rejoicing"). The week that follows Thomas Sunday is called Thomas Week, and a number of the hymns from Thomas Sunday are repeated throughout the week, as well as new ones from the Pentecostarion developing the theme of Thomas Sunday.
- Quasimodo, protagonist of the 1831 French novel The Hunchback of Notre Dame by Victor Hugo, was found abandoned on the doorsteps of Notre Dame on the Sunday after Easter, 1467 CE. In the words of the novel:
He [sc. archdeacon Claude Frollo, Quasimodo's adoptive father] baptized his adopted child and called him Quasimodo; whether it was that he chose thereby to commemorate the day when he had found him, or that he meant to mark by that name how incomplete and imperfectly molded the poor little creature was. Indeed, Quasimodo, one-eyed, hunchbacked, and bow-legged, could hardly be considered as anything more than an almost.
- ↑ The full line is "Quasi modo geniti infantes, rationabile, sine dolo lac concupiscite", from Catholic Encyclopedia listing for Low Sunday, roughly translated as "As if just now, you are born babies, thus you desire the Word like milk...." Accessed November 18, 2009.
- ↑ Hugo, Victor (1996) . The Hunchback of Notre-Dame. Penguin Books. pp. 147–148. ISBN 978-0-140-62222-5.
- Thomas Sunday Orthodox icon and synaxarion
- "Low Sunday". Catholic Encyclopedia. New York: Robert Appleton Company. 1913. http://en.wikisource.org/wiki/Catholic_Encyclopedia_(1913)/Low_Sunday.