How a beam of sunlight was directed on Lord Ram’s forehead in Ayodhya temple

We explain the science behind Ram Lalla’s Surya Tilak.

Step 1: Predict the Sun’s position (each year)

When following the Gregorian calendar, the date of Ram Navami (the Hindu festival celebrating the birth of Lord Ram) varies each year. This is because the Gregorian calendar is a solar calendar (based on Earth’s revolution around the Sun — one revolution equals to one year), while the Hindu calendar is a lunar calendar (based on the Moon’s revolution around Earth — one revolution equals to one month).

A solar year has roughly 365 days, whereas a lunar year is roughly 354 days long.

Given that the IIA team’s brief was to channelise the sun’s rays such that they fall on the Ram idol’s forehead on Ram Navami, its first task was to calculate the position of the Sun in the sky on that day in any given year.

Annapurni Subramaniam, Director, IIA, told The Indian Express: “There were two challenges to address, the first of which was to estimate and predict the position of the Sun in the sky on a particular day in a particular year.”

Step 2: To channelise the Sun’s rays

After astronomers estimated where the Sun will be in the sky, their second task was to channelise the sunbeam “in a manner that it will fall on the idol’s forehead for a certain amount of time,” Subramaniam said.

The IIA team, which began designing the apparatus three years ago, proposed a four-mirror-and-four-lens array for this purpose. “The first mirror, responsible for receiving the sunlight, has to be positioned at an angle along the path of the sun rays,” she explained.

The light will then be reflected to three other mirrors, and will pass through four lenses until it is of the desired intensity, and will be directed to the idol’s forehead. The mirrors directed the beams while the lenses made them converge to the required intensity.

How the system works. (Source: IIA)

This opto-mechanical system operates on a principle similar to that of a periscope — like the ones you used to make for school projects (see graphic). Given that the sun’s position vis-à-vis the first mirror will vary each year, a specially designed 19-gear system was built to make requisite adjustments.

“Once a year, one tooth of the gear will have to be manually turned so that the angle of the pickup mirror (first mirror) is adjusted, and it is ready to capture the Sun’s rays,” Subramaniam said.

The number 19 was chosen to correspond to the Metonic cycle — a period of 19 years in which there are 235 lunar months, after which the Moon’s phases recur on the same days of the solar year. This means that every 19 years, the system will effectively reset, and the cycle will then begin again.

Not the final setup

The glass tube set-up, housing the lenses and mirrors, runs from the third floor of the temple, all the way to the sanctum sanctorum. This huge set-up requires precision handling, and a clean environment to operate. The IIA team was especially concerned about the final mirror positioned inside the sanctum sanctorum, where general activity and havans can lead to soot and dust gathering.

“Care must be taken to prevent the fumes (from the sanctum sanctorum) from reaching the final mirror. The lenses and the mirrors should not get clouded,” Subramaniam said. This is why the design allows the final mirror to be opened and cleaned, if required.

Since the construction of the temple is yet to be complete, the installation of the final system has not yet taken place. On Wednesday, for the temple’s first Ram Navami celebration, a modified version of the system, having four mirrors and two lenses, was deployed from the second floor of the temple building.