It comes 40 days after the traditional day for celebrating the birth of Jesus in the Western church, December 25th, and therefore corresponds to the day on which his mother, according to Jewish law (see Leviticus:12), should have attended a ceremony of ritual purification, as described in the gospel of Luke:2:22-39. Thus its formal name within Catholicism is the Feast of the Purification of the Virgin Mary.
In the Eastern Orthodox church, however, Jesus's birth is celebrated on January 6th, and the feast of the Purification therefore falls on February 15th. This is the earliest date recorded for its observance.
In the United States, Candlemas became known as Groundhog Day.
Modern Pagans regard Candlemas as a christianisation of an ancient pagan festival, Imbolc, which was celebrated in pre-Christian Ireland at about the same time of year; the evidence that this festival was widespread is however slender, and there is no reason to suppose that an Irish festival would have influenced the practice of the Greek church in the early fifth century. It is more plausible that some forms of pagan observance were incorporated into Christian practice in north-western Europe.