William Jones, the Welshman who invented π

This symbol does not display for iOS. (Sadly lots of Unicode mathematical symbols are missing from iOS, which is why those hacks for showing text in Fraktur or italics don't work either.)

The next proper Pi Day is in a bit over a thousand years, on 3141-5-9.

Of course, if you think that's a bit long to wait for, the one after that is 28000 years afterwards, on 31415-9-6. I'm looking forward to it!

Because they sometimes (and apparently historically) write 3/14:

https://en.wikipedia.org/wiki/Date_format_by_country

Because we don't have 14 month and otherwise they would never be able to celebrate this glorious occasion.

(Really, the month/day format is stupid, but for novelty purposes that shouldn't matter?)

You're getting downvoted pretty hard, but I generally agree. Using tau (2π) feels much more natural. It seems like, in physics, 90% of the time we use π, it shows up with a 2 next to it. And the article you linked has a good point; if we called τ a "turn", statements about getting arc lengths from angles and radii would translate to natural language much better. τ not only corresponds to full rotations, but also to full periods of sine and cosine functions.