(CNN) — Every spring, thousands of monks gather at the ancient Borobudur Temple in Java, Indonesia, on the most important day on the Buddhist calendar: Buddha Day.

Also known as Waisak Day or Vesak Day, the holiday marks the birth of Gautama Buddha -- the father of Buddhism, who is responsible for the religion's core teachings.

Robe-clad monks circle the 9th-century temple -- the world's largest Buddhist temple and a UNESCO heritage site -- to meditate, chant sutras and release an ocean of glowing lanterns into the night sky.

It's just one of many celebrations taking place across Asia this month as worshippers ring in the holiday at the region's most beautiful temples, from lantern festivals at Seoul's Jogyesa Temple to rituals at Yangon's golden Shwedagon Pagoda.

Indonesia's Borobudur Temple. Ulet Ifansasti/Getty Images AsiaPac/Getty Images

About Vesak Day

Born in Nepal in 567 BC, Gautama Buddha -- or Prince Siddhartha Gautama at birth -- was the son of a tribal leader.

As an adult, he founded a sect of wandering ascetics and the community eventually evolved into a religion after his death at 80 years old.

Today, over 488 million people -- or roughly 9% of the world's population -- practice Buddhism, nearly 99% of which are located in the Asia-Pacific region.

Each year, on the full moon of the month of Vesakha (usually falling in May or June in the western calendar), millions of Buddhists around the world take part in Vesak Day celebrations.

Not only does the date of Vesak Day change year after year, but it can also be different among cultures, depending which calendar they subscribe to.

In China and Hong Kong, for example, which follow the Chinese lunar calendar, worshippers observe Buddha Day on the eighth day of the fourth month (usually in early May).

So while Buddhists in Hong Kong marked Buddha Day on May 3 this year, Thailand celebrates on May 10.

The holiday goes by dozens of names -- but many countries unofficially refer to it as Buddha's Birthday or Buddha Day.

It celebrates three important events of Buddha's life: birth, enlightenment, and death -- said to have occurred on the same calendar day, albeit many years apart.

Celebrations around the world

From Thailand to South Korea, Myanmar, China and Malaysia -- every country has its own traditions, each symbolizing various aspects of Buddha's life or teachings.

Home to 255 million Buddhists -- the world's largest Buddhist population -- China sees one of the most widespread celebrations.

Most of the action revolves around Buddhist temples, where people light incense and leave offerings.

In South Korea, the holiday comes to life in a Lotus Lantern festival, best viewed at Seoul's Jogyesa Temple.

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Temples are draped in thousands of colorful paper lanterns. It's also common for temples to offer bibimbap and tea to those who visit on the holiday.

Meanwhile, in Sri Lanka, people decorate their homes with paper lanterns. Colombo's Gangaramaya Buddhist Temple hosts a colorful Vesak Day festival.

In Ipoh, Malaysia, Buddhist devotees practice the ritual of "Sunning Buddha."

At Ipoh's Enlightened Heart Tibetan Buddhist temple, monks place a sacred Tibetan Buddhist painting -- called a "Thangka" -- in the sun to absorb its powers.

The energy is believed to promote peace, health, and harmony for the rest of the year.

And in Nepal, where Buddha was born? Thousands of Buddhists flock to Lumbini, his birthplace, where they donate supplies to disadvantaged communities and pay tribute to monasteries.