Tibetan Buddhism conjures up images of prayer wheels, mandalas and prostration, but there is one other indispensable item: a calendar. Aside from some textbooks, the Tibetan Annual Almanac is the most widely circulated book in the Tibet autonomous region. The information it contains is critical to everyday life, especially for farmers, herders, doctors and Buddhists.

The Astronomy Calendar Research Institute of the Tibetan Hospital in Lhasa helps make the almanac using astronomy based on the tantric Kalachakra: the wheel of time.

Dating back more than 2,000 years, the Kalachakra describes eclipses as an alignment of the sun, moon and appropriate lunar nodes, exactly the same as modern astronomy.

It shows the specific dates and times of eclipses, auspicious days for farming and other activities, as well as the timing of Buddhist festivals.

Digital calculation

For thousands of years, these calculations were done by hand, according to Yinba, director of the institute.

All the calendarists in Yinba's teams have gone through strict training in either monasteries or research institutes. They must memorize sophisticated formulas and be adept at mental arithmetic, as no scratch paper is ever available.

Instead, they have traditionally made their calculations by writing with a stick in a tray of sand, quickly memorizing the numbers as they were ceaselessly erased for the next calculation.

To make the figures easier to handle, ancient astronomy masters devised a set of "calculation verses" that calendar makers chant while calculating.

In an attempt to speed up the time-consuming work, the institute brought in calculators in the 1990s - but the astronomical data proved too much for these early devices.

Yet as computers became more advanced, Yinba and his team began to develop a set of algorithms on astronomical changes and the changing days.

Key in a few numbers into the system today, and with a click of the mouse, all 52 pages of astronomical data for 2016 will pop up onto the screen in two or three seconds.

Using these algorithms, the institute has now published the first Tibetan calendar book covering AD 1 to 2100.

In the past, it took an astronomical master and his apprentices more than 30 years to produce a new calendar, combining the four schools of traditional Tibetan calendar making while working with both the Gregorian calendar and Chinese lunar calendars.

Yinba said manual calculation is still used to double check, but the computers allows more time to be spent on research and training students.

A vital practice

Astronomy has been viewed as one of the toughest courses in traditional monastic education. The subject has little to do with stargazing but is closely tied with Buddhist religious practices and people's everyday lives.

In the Kalachakra Tantra, Buddha presented not only an external system dealing with the motion of planets and the ways to measure time, but also an internal system witnessing the cycles of energy and breath through the human body that is closely related to the external system.

That is why when eclipses appear, Buddhists are inspired to chant mantras, meditate or engage in other practices that they believe will to take them closer to enlightenment.

It also explains why all medical students must study astronomy to a certain level in traditional monasteries - astronomical knowledge serving as a guide for when to collect medicinal herbs or use therapies such as bloodletting.

The Tibetan calendar's utility has ensured knowledge of it has been passed down from generation to generation. It is used by meteorologists, while farmers use it as a reference for planting and pasturing.

Looking back to his youth studying with senior monks in Gansu province and the Tibet autonomous region, Yinba said he was grateful to the astronomy masters of the past.

"Tibetan astronomy is a unique part of our culture. To keep it alive, we must not stand still, but make progress," he said.

While the algorithms are yet to be perfected, Yinba spelled out another dream: building an observatory in Lhasa.

"I wish more people could look to the stars through astronomical telescopes and know more about the universe," he said.