LONGITUDES, SYZYGIES, AND INSTRUMENTS IN REGIOMONTANUS' CALENDAR FOR 1475-1531.

Instruments and tables in Regiomontanus' calendar published in 1474 are analysed and explained. It is shown that Regiomontanus used the Alfonsine Tables corrected for the longitude time difference between Toledo and Nuremberg. It is also shown that for the syzygy and eclipse times he used apparent solar times. The syzygy tables of George Peurbach may have been used to correct from mean to true syzygies. The calendar also contains an instrument for converting between equal and unequal times, a volvelle for finding the true longitude of the Moon, a quadrant tool for the construction of a horizontal sundial, and a universal vertical sundial. The construction and workings of these instruments are analysed. [ABSTRACT FROM AUTHOR]