Tibetan Buddhism conjures up images of prayer wheels, mandalas and prostration, but there is one little-known, indispensable item: a calendar.

Aside from some textbooks, the Tibetan Annual Almanac is the most widely circulated book in Tibet. The information it carries is critical in everyday life, especially for farmers, herders, doctors and Buddhists.

The Astronomy Calendar Research Institute of the Tibetan Hospital in Lhasa leads routine 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.

On these calendars, one can find the specific dates and times of eclipses, auspicious days for farming and other activities, as well as the timing of Buddhist festivals.

MANUAL CALCULATION VS DIGITALIZATION

For thousands of years, these calculations have been done manually, 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 calculate with a stick on specialized sand-boards, about one-meter long and less than 20-cm wide, and results must be quickly memorized as numbers are ceaselessly erased from the sand for the next calculation.

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

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

When computers entered China, Yinba and his team began to use them and have since developed a set of algorithms on astronomical changes and changes of days.

Key in a few numbers into the system, and with a click of the mouse, all astronomical data for the year of the fire monkey (2016) will pop up onto the screen in two or three seconds, all fifty-two pages of it.

With the algorithms, the institute has published the first Tibetan calendar book covering the years 1 to 2100 A.D.

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

Yinba said manual calculation was still used as a double check, but with computers as an alternative, more time is spent on training students and on research.

STRONG VITALITY

In traditional monastic education, astronomy was viewed as one of the toughest courses. The subject has very little to do with stargazing but is closely tied in 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 other engage 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 is particularly useful, for instance, when doctors use external therapies such as blood-letting or when herbs are collected from the mountains.

Calendar makers agreed that it is the utility of their product that has ensured the knowledge is passed intact from generation to generation. The calendar is used by meteorologists. Farmers use it as a reference for planting and pasturing.

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

"Tibetan astronomy 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.