Most people have a good sense of the motion of our solar system, in part because it's such a part of our lives. The rotation of the Earth makes for day and night; our planet's revolution around the sun marks a year. But fewer Earthlings grasp the larger picture—that our solar system is just one among many orbiting a supermassive black hole at the center of the galaxy. The sun moves, too.

David Sneider, a 26-year-old software entrepreneur from San Francisco, had this epiphany during a hike four months ago. He wondered aloud how people's perceptions would change if they really realized the one fixed point in their celestial understanding, the mighty sun, was also in flux.

"We were talking about the cultural mysticism of planet locations, which is especially important in people's lives here in California," he said. "People say, 'Mars is in retrograde so we're in for a stretch of bad luck. I'll look carefully before crossing the street.' It's like the time before the Copernican revolution."

To try to right this situation, Sneider and three other people, none of them astronomers, invented a holiday. It's called Galactic Tick Day, this year to be celebrated on September 29. Here's how it works.

Earth, as part of the Solar System, travels around the galactic center of the Milky Way every 225 million years. Waiting a couple hundred million years to celebrate a holiday is no fun, so they settled on a smaller slice to commemorate our vast cosmic movement. They selected a centi-arcsecond of this rotation to be the unit of measurement. It's called a Galactic Tick, and it represents 1/129,600,000 of our solar system's orbit around that black hole at the center of the Milky Way.

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On earth, this Galactic Tick happens every 633.7 days. That's 1.7 years between celebrations. "The whole thought is to scale down to something more digestible, to a human time scale," Sneider said. "And it's sort of fun, because the date will always change. It won't always be September 29." The website notes that GTD can be celebrated anywhere in the solar system.

To get a start date for the holiday, the foursome selected the baseline for Galactic Tick Day as when Hans Lippershey filed his patent for the first telescope in October 1608. "There is a certain amount of arbitrariness with the numbers we picked," Sneider conceded. But the point of Galactic Tick Day is to celebrate the idea that human beings are clever and self-aware enough to even know we're part of a vast cosmos. Sneider hopes to inspire a new perspective in anyone who can look up and imagine our entire solar system careening through the galaxy, grounded in science but no less awe inspiring than an astrology chart. "As soon as you intuit this, it becomes an easy way to gain a wider perspective," he says.

Sneider's group has no sponsors and isn't asking for money. Their website doesn't accept donations. "We have no monetization as an end game," he said. "This is entirely 100 percent non-commercial."

There are two inaugural celebrations of GTD planned for September, one in San Francisco and another in Ottawa, Canada. In California, 175 people have already signed up to attend the Tick event, including a speaker from Stanford discussing new research into gravity waves. "Our hope is that people like the idea and host their own events," Sneider says. "Anyone making money would really fly in the face of this thing."

The founders of Galactic Tick Day hope the holiday will inspire new ways of thinking, the same way astronauts view the Earth in a different way after seeing our planet from orbit. "We're hoping that the effect will be the same," he said. "That deep sense that we are connected."

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