The blue moon is rare, that’s a fact. But the expression <once in a blue moon> stays with us to remind us of things rare, mysterious, out-of-ordinary and – well, blue. What to do once in a blue moon? 1. Go for your prreciouss: put a finger on a thing that you covet and go for it. An expensive treat, a collectible or even a person; whatever makes you feel you hold the keys to the universe’s secret. Something like seeing Tosca in the Teatro Antico di Taormina, with a view of the sea and of Etna in the backdrop (possibly with incandescent lava on top). 2. Venture into the mystery:…