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Since today is 29th February, a leap-year-themed post is in order.  This one answers the question you’ve all been asking: how are leap years represented on astrolabes? First, a word about the Julian calendar.  Most astrolabes were made before the Gregorian calendar reform (1582), and that made life a bit simpler for instrument-makers.  In the Julian calendar, leap years happen every four years, without exception.  On the other hand, the Gregorian calendar got rid of 3 leap da

I’m just back from two very enjoyable days in Oxford, at the Bodleian Library’s wonderful new Weston Library.  Apart from looking at some fascinating and important manuscripts, I snuck a peek at their Marks of Genius exhibition, which I’d strongly recommend if you’re in town (it’s free, and on until 20 September). The view from the David Room on the fifth floor of the Weston Library is pretty special: …though I do still have a soft spot for Cambridge’s University Library – th