Yesterday we only told part of the story about the amazing sundial in the church of Santa Maria degli Angeli et dei Martiri in Rome. There are actually two sundials set into the floor of the church, not one.
There is a long brass strip (above) which allows observers to work out the dates of equinoxes and solstices, as the sun moves relative to the earth through the year. That information is needed for making accurate calendars and also to establish the correct dates for Easter.
The second sundial tracks the movement of the Pole Star – a more distant sun – through the year, shown in a series of ellipses on the floor (below). There is plenty of interesting science in this church!