In April (the month of Bak), when the sun moves from the Meena Rashiya (House of Pisces) to the Mesha Rashiya (House of Aries) in the celestial sphere; Sri Lankans begin celebrating their New Year or Aluth Avurudhu (in Sinhala) . It marks the end of the harvest season . On the day of celebrations, the sun is directly above Koggala (where a sun devale can be found).
However, unlike the Western celebration of the new year at midnight on December 31st, the Sri Lankan New Year begins at a time determined by astrological signs. Also unlike western traditions; the ending of the old year, and the beginning of the new year occur several hours apart from one another (this span is determined by astrology as well) - this period is, aptly enough, referred to as the nona gathe (neutral period). During this time Sri Lankans are, according to custom, encouraged to refrain from material pursuits, and engage solely in religious activities (buddhists)and traditional games.
Cultural rituals begin shortly after the beginning of the new year with the cleaning of the house and lighting of an oil lamp.
Families indulge in a variety of rituals which are carefully determined by astrological calculations - from lighting the fire to making the kiri bath, (milk rice) to entering into the first business transaction and eating the first morsels.
Once these are done, the partying really begins as families mingle in the streets, homes are thrown open and children are let out to play. The ubiquitous plantain is dished out alongside celebratory feasts of kaung (small oil cake) and kokis (crisp and light sweetmeat, originally from the Netherlands).
Aurudu has become an important national holiday for both the cultures of the Sinhalese Buddhists and the Tamil Sri Lankans, and is unique as such, as it is not celebrated in the same manner elsewhere in the world (some countries do celebrate a similar festival on the same date or a near date) .(wiki)