The New Moon Celebration was an annual festival held between the Northern and Southern Water Tribes during the antebellum period before the Hundred Year War. It was a commemoration held to reunite the two polar Water Tribes. Considering Avatar Kuruk's allegory while talking to Aang in the Spirit World, the celebrations were seemingly scheduled to correspond with a new moon. It was at one of these festivals that Kuruk met the love of his life, Ummi, sometime prior to 312 BG.
The New Moon Celebration was a time when the Northern and Southern Water Tribes could unite. Family and friends separated by miles of land and sea, literally on opposite sides of the globe, were able to see each other and reunite during these festivals. Judging by the festival Kuruk attended, there was a certain air of formality and spirituality present during these festivities, with many tribesmen having dressed up for the occasion. Despite this, the festivals were also casual social functions, as their reason for being was to bring citizens together and have them mingle with one another.