Find this orientation by looking through the crystal at the sky at a time when you can see the sun, mark the sun's direction on the crystal, and your mark will always point towards the sun when you match the beams from even a tiny patch of blue in an otherwise overcast sky.
This year, that work would be the star feature at Marlborough Fine Ar t: a dazzlingly beautiful, sun-drenched Mark Rothko canvas, seeped in burnt orange and the palest pink, and dated 1954.