Calan Mai ([ˈkhaːlan ˈmaːj] "Calend (first day) of May") or Calan Haf ([ˈkhaːlan ˈhaːv] "Calend of Summer") is a May Day holiday of Wales held on 1 May. Celebrations start on the evening before, known as May Eve, with bonfires; as with Calan Gaeaf or November 1, the night before (Welsh: Nos Galan Haf) is considered an Ysbrydnos or "spirit night" when spirits are out and about divination is possible.