Today is the birthday of Queen Elizabeth II (her real birthday, as opposed to the day everyone in England celebrates it).
But more importantly it is the birthday of Professor Roger Bowley, one of Sixty Symbols regular contributors.
He's also the owner of many loud shirts - but let's not discuss that!
It was a milestone birthday (somewhere midway between between 60 and 70) and this means Professor Bowley's retirement from academic life is imminent.
However today he promised me he'll still be chipping in with contributions to Sixty Symbols.
It seems like just yesterday I was knocking on his office door and introducing myself as a guy planning to make videos about physics.
I'd been told he might be good at it.
Roger seemed bemused but eventually agreed to do it.
And he is good at it.
Here are just some of his videos since that fateful day: