Today is Visakh Bochea (វិសាខបូជា), a major Buddhist holy day and a public holiday in Cambodia. The day celebrates three events in the life of the Buddha (Siddhattha Gotama): birth, enlightenment, and death. These events are commemorated in Buddhist countries, and other nations in Asia, on a variety of days, such as, https://www.bookofdaystales.com/buddhas-birthday/ but in Cambodia, and elsewhere (Sri Lanka, Laos, Myanmar, Malaysia), they are all collapsed into one day – the full moon of the lunar month of vesākha. The generic name Vesak, from the Sanskrit Vaiśākha, is used to designate the festival worldwide, and it falls on different days in April or May depending on local custom. This year (2021) the vast majority of Asian countries will celebrate Vesak on May 26th, but, for reasons that are not clear to me, Cambodia is the odd one out. May is more usual: https://www.bookofdaystales.com/may-full-moon/
The actual dates of any events in the Buddha’s life are, of course, completely unknown. Best guess by modern scholars is that he was active in the 5th century BCE, but pinning down the years, let alone the dates, of his birth and death are impossible at this point. Conflating them together with his day of enlightenment is merely a convenience of observance, and many Buddhist cultures separate out the events for individual celebration.
On Vesak Bochea, devout Buddhists and monks assemble in local temples before dawn with candles for the ceremonial hoisting of the Buddhist flag and the singing of hymns in praise of the holy triple gem: The Buddha, The Dharma (his teachings), and The Sangha (his disciples). Devotees may bring simple offerings of flowers and incense. They are reminders that all things decay or burn out just as life is subject to decay and destruction. Devotees are also encouraged to partake only of vegetarian food for the day and to avoid alcohol. Here in Phnom Penh, stores owned by the devout do not sell alcohol for several days prior to Vesak. Also, birds, insects, and animals are released by individuals on this day in a symbolic act of liberation – giving freedom to those who are in captivity, imprisoned, or tortured against their will. While I understand the symbolism, I have always been troubled by the sight of scores of people lining the Mekong river front, and outside pagodas, selling caged wild birds to be set free. It’s not so much the caged birds themselves, but the paradoxical karma involved in trapping them in order to liberate them. Doesn’t it just balance out? (“Here little birdie – I am going to trap you so that I can set you free.”)
Celebrating Vesak also involves making a special effort to bring happiness to the unfortunate such as the aged, the handicapped, and the sick. The devout distribute gifts in the form of cash and food, or volunteering in various charitable homes throughout the country. Vesak is a time of joy and happiness expressed in simple pleasures, and not the great blowout feasts common at other festivals, such as New Year. Vegetarian cooking is the norm. Here is a video giving a recipe for Khmer សម្លម្ជូរ គ្រឿង (samlar machu kreung), a sour lemongrass soup.