How to play the Gnomon

A round

Each day one famous building stands under that day's sun at an hour kept secret. Its shadow is the only clue.

Set an hour and read it. The sun swings to your reading and back, and the shadow your reading cast stays faint on the plate, so you can compare it with the real one.

You have six readings. One within ten minutes of the hour finds it.

Reading a shadow

A shadow points away from the sun. Morning shadows fall toward the west, afternoon shadows toward the east.

A long shadow means a low sun: early in the morning or late in the day. A short one means the sun stood high, nearer noon.

In the north the sun crosses the southern sky, so the shadow at noon points north. In the south it is the other way round.

The compass round the plate says where north is.

The same puzzle for everyone

Everyone plays the same shadow on the same day, here and in Sol for iPhone. A shared result gives the score and the link, and never the hour.

A day you missed is still open: every number so far stands on one page.