National Juggling Day

What the day is

National Juggling Day, now more often called World Juggling Day, is observed on the Saturday closest to June 17. That date is the International Jugglers' Association's own founding anniversary, June 17, 1947; the name changed to World Juggling Day in 1995 to reflect the group's international reach, though the older name still circulates. Juggling is also one of the few skills whose underlying mathematics was worked out thousands of years after people started doing it.

Origin and background

In the 1980s several people independently arrived at a notation now called siteswap, which writes a juggling pattern as a sequence of digits. Each digit says how many beats will pass before that particular throw is caught and thrown again, so a larger number means a higher throw. The basic three-ball cascade is a repeating 3, and the five-ball version a repeating 5.

Two useful things fall straight out of it. The average of the digits in a valid sequence equals the number of objects being juggled, which gives an instant test of whether a pattern is even possible. And sequences that look perfectly reasonable can be proved impossible, because two balls would have to arrive in the same hand on the same beat. The notation turned pattern invention from trial and error into something closer to searching, and a good deal of modern juggling consists of patterns that were found on paper first and learned afterward.

The physical learning is interesting for a separate reason. A frequently cited study scanned adults before and after they spent three months learning a three-ball cascade, and found measurable increases in gray matter in regions that handle visual motion. The changes partly receded once people stopped practicing. It was among the clearest demonstrations that adult brains change structurally in response to learning a physical skill, rather than only changing how they operate.

Teachers are consistent on the practical point: the difficulty is not catching but throwing. Throws that reach the same height and land in the right place make catching close to automatic, which is why beginners are told to practice throwing and not to catch at all.

How to take part

• Start with one ball, thrown hand to hand at eye height.
• Practice throwing and letting them drop. Catching follows accurate throwing.
• Look up siteswap and work out what the pattern 531 does.
• Stand in front of a bed or a sofa so retrieving them is less tedious.