Magha Puja

        Māgha Pūjā, Makha Bucha, or the Full Moon of Tabaung (Khmer: មាឃបូជា; Lao: ມະຄະບູຊາ; Thai: มาฆบูชา(Pronunciation)) is an important Buddhist festival celebrated in Myanmar (Burma), Thailand, Cambodia, and Laos on the full moon day of the third lunar month (this usually falls in February). The third lunar month is known in the Thai language as Makha (Pali: Māgha); Bucha is also a Thai word (Pali: Pūjā), meaning "to venerate" or "to honor". As such, Makha Bucha Day is for the veneration of Buddha and his teachings on the full moon day of the third lunar month.

        The spiritual aims of the day are: not to commit any kind of sins; do only good; purify one's mind.

        Māgha Pūjā is a public holiday in Burma (Myanmar), Cambodia, Laos and Thailand - and is an occasion when Buddhists tend to go to the temple to perform merit-making activities.

Origin

Māgha Pūjā day marks the four auspicious occasions, which happened nine months after the Enlightenment of the Buddha at Veḷuvana Bamboo Grove, near Rājagaha in Northern India. On that occasion, as recorded in the commentary to the Mahāsamayasutta, DN-Comm 20) four marvellous events occurred:

1. There were 1,250 Arahata, that came to see the Buddha that evening without any schedule.
2. All of them were Arhantas, the Enlightened One, and all of them were ordained by the Buddha himself.
3. The Buddha gave those Arhantas principles of Buddhism, called "The ovadhapatimokha". Those principles are: - To cease from all evil,- To do what is good,- To cleanse one's mind;
4. it was the full-moon day.

The Buddha gave an important teaching to the assembled monks on that day 2,500 years ago called the 'Ovādapātimokha' which laid down the principles of the Buddhist teachings. In Thailand, this teaching has been dubbed the 'Heart of Buddhism'.

Thailand

1. In the evening of Magha full-moon day, each temple in Thailand holds a candlelight procession called a wian tian (wian meaning circle; tian meaning candle). Holding flowers, incense and a lighted candle, the monks and congregation members circumambulate clockwise three times around the phra ubosot (ordination hall) - once for each of the Three Jewels – the Buddha, the Dharma, and the Sangha.
2. Tum Boon: Making merit by going to temples for special observances and join in the other Buddhist activities.
3. Rub Sil': Keeping the Five Precepts. Practise of renunciation: Observe the Eight Precepts, practise of meditation and mental discipline, stay in the temple, wearing white robes, for a number of days.

Reference : http://th.wikipedia.org/wiki/%E0%B8%A7%E0%B8%B1%E0%B8%99%E0%B8%A1%E0%B8%B2%E0%B8%86%E0%B8%9A%E0%B8%B9%E0%B8%8A%E0%B8%B2