The Clock of the Long Now
Inside a mountain in West Texas, a mechanical clock is being built to keep time for the next ten thousand years.
A clock for the long now
Most clocks are built to tell you what time it is right now. The Clock of the Long Now is built to make people think about the next 10,000 years. Its designer, Danny Hillis, built some of the world's fastest supercomputers in the 1980s. The Science Museum in London neatly describes his clock as the opposite: the world's slowest computer.
Hillis began writing publicly about a millennium clock in 1995, in a column for Wired, according to PBS NOVA. The same NOVA article also carries a photo caption saying he first conceived the clock in 1986, so accounts differ on exactly when the idea began.
In 1996 Hillis and Stewart Brand formed the Long Now Foundation to pursue it, and musician Brian Eno suggested the name. As the Science Museum's curator of time explained, now means this moment give or take a day, nowadays stretches to about a decade, and the long now covers 10,000 years either side of the present.
The foundation writes years with five digits, as in 02026, which gives some sense of the timescale it has in mind. NOVA reports that the team chose 10,000 years because that is roughly how long agricultural civilization has existed.
See also: how astronomers count days across centuries on OnlineClock.app.
The vision: a slow, slow clock
As NOVA describes Hillis's original vision, the clock ticks once a year, its century hand advances once every 100 years, and a cuckoo comes out once every millennium.
Brand hoped the clock would do for thinking about time what the first photographs of Earth from space did for thinking about the environment: give people an image they could not forget.
Hillis set out five design principles: longevity, maintainability, transparency, evolvability and scalability. In practice that means the clock should show the correct time for 10,000 years, be repairable with bronze-age technology, be understandable by close inspection, be improvable over time, and work the same way whether it is built on a tabletop or inside a mountain.
The first prototype
A team led by Alexander Rose began building the first prototype in San Francisco in 1997. According to the Science Museum, it first ticked moments before the end of New Year's Eve 1999.
It is a weight-driven clock with a torsional pendulum, which twists back and forth rather than swinging, and it beats twice a minute. Two falling weights, wound every few days, keep it going. Its timing passes through an oversized escapement to a mechanical computer that updates the dial once an hour.
The dial shows the position of the sun, the phase of the moon, the stars visible overhead and the slow precession of the equinoxes, the slowest-moving display of all. The prototype then moved to London, where it became the final exhibit in the Science Museum's Making the Modern World gallery.
The museum's collection lists it at roughly 2.7 m by 2 m, weighing 181 kg, and made of bronze and steel. It suggests checking ahead that the clock is on display before you visit.
Inside the mountain
The full-scale clock is being built inside a mountain in West Texas, near Van Horn according to the Science Museum. The Long Now Foundation credits Jeff Bezos with providing the location and most of the funding, and NOVA, writing in 2018, put the price tag at 42 million dollars.
NOVA dates the groundbreaking to 2010. The Long Now Foundation's timeline picks up from there: the 500-foot shaft was bored out in 2011, a robotic saw then spent nearly two years cutting a spiral staircase into the rock, and the power storage system was tested in the workshop in 2012.
According to the foundation, the entrance tunnel sits 1,500 feet above the desert, the shaft is 12 feet wide, and the air inside stays at a steady 55 degrees Fahrenheit all year. A sapphire-windowed dome 12 feet across caps the top.
The parts are built to the same scale. Some gears are more than 8 feet across and weigh 1,000 pounds each, and the main weights weigh 10,000 pounds apiece, one of them a bronze, egg-shaped shell filled with concrete. The materials were chosen to last: titanium, ceramics, quartz, sapphire and 316 stainless steel, with ceramic bearings that need no grit-attracting oil.
Powered by the sun and by visitors
The clock is entirely mechanical. Sunlight warms a chamber of air, and the daily heating and cooling moves a graphite cylinder that winds the pendulum. The foundation says this can keep the pendulum going for about 500 years without human help.
NOVA explains the principle in simple terms: air moves between a tank warmed by the sun near the surface and a cooler one inside the mountain. That temperature difference of a few tens of degrees is enough to lift a weight, and no electricity is involved.
A solar synchronizer, also driven by sunlight, detects solar noon so small errors do not build up. A part the foundation calls the Equation of Time cam accounts for the roughly 15-minute difference that can open up between sun time and clock time over the year.
To save energy, the clock keeps time continuously but updates its displays only when someone comes. Visitors wind it with a capstan, a job that takes two or three people, which brings the dials up to date and can ring its bells.
Ten thousand years of chimes
Brian Eno worked with Hillis on the clock's chime generator, which rings ten bells. The Long Now Foundation says it can produce more than 3.5 million unique bell sequences, enough for a different one on every day the clock is visited over 10,000 years. Eno's album January 07003 offers a preview of what they might sound like.
The project has moved slowly, as befits it. The drive weight, winder and main gearing were assembled underground in 2018, the bells first rang in 2022, and at solar noon on the summer solstice of 2025 the clock synchronized with the sun for the first time.
In summer 2026, the foundation said the West Texas clock had been handed over to Bezos, who plans to add his own anniversary displays before commissioning is finished and the clock opens to visitors, with Long Now members given priority. The foundation's clock page gives no opening date.
Texas may not be the last of these clocks. The foundation says Hillis is working with it to find a less remote site for the next monument-scale clock, and the Science Museum's curator noted in 2013 that land had been bought for another clock on a mountain in eastern Nevada, beside Great Basin National Park.
See also: the date of the next summer solstice on OnlineClock.app.
Questions people ask
Can you visit the Clock of the Long Now?
Not yet. As of the Long Now Foundation's summer 2026 update, commissioning was still under way, and the clock is due to open to visitors afterward, with priority for Long Now members. No opening date has been announced.
Where is the 10,000-year clock?
Inside a mountain in West Texas, near Van Horn, on land provided by Jeff Bezos. The first prototype is in the collection of the Science Museum in London.
How is the Clock of the Long Now powered?
Daily temperature changes from sunlight wind its pendulum, a solar synchronizer keeps it aligned with solar noon, and visitors wind it to update the dials and ring the chimes.
Who designed the Clock of the Long Now?
Danny Hillis designed it with the Long Now Foundation, which he formed with Stewart Brand in 1996. Alexander Rose led the project design and Brian Eno helped design the chimes.