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Our organic alarm clock has now taken to jumping on the bed at about 5 in the morning and purring very loudly in an attempt to persuade us it’s breakfast time. It’s not surprising, since sunrise (and therefore cat-rise, if not Marcus-rise) is becoming earlier and earlier.

Daylight hours are now long – in fact the South Pole is now in non-stop daylight. If you’re there with no cloud present you’d see the sun circle the sky, at fairly low elevation. A horizontal surface would get non-stop daylight, but a vertical surface obviously wouldn’t. About half the time it would be lit, and half the time in shadow, with the sun behind it.

So here’s the brain teaser. In the course of a 24 hour day, is it possible for a vertical wall to be lit for more than 12 hours (clouds and other obstacles not getting in the way, of course)?

And, if so, where in the world would the wall be, what day of the year would it be and what is the maximum time it could spend illuminated?

No prizes, other than a chance to feel smug.