• 1564, (Portugal)
• 1 bound volume, manuscript on parchment, 29 folios;
• 31,5×21,5×1,5 cm
• Portuguese National Archive of Torre do Tombo
• Ref Code: PT/TT/MSLIV/0869

Many scientific and technical developments made during the 16th century, in response to the new needs of oceanic navigation, were adaptations of previously existing procedures. Both nautical instruments and nautical techniques were frequently adapted from instruments and methods that astronomers and astrologers had used for many centuries.

Astronomical techniques were also adapted to solve navigation issues, such as calculating the current latitude, a crucial operation for any venture on the high seas. This process of progressive adaptation was complex and required the joint collaboration of sailors and scholars such as mathematicians, professional groups that had very little in common up to that time.

The manuscript presented here records astronomical data necessary for the determination of latitude. More specifically, it tabulates the values of an astronomical parameter – the declination of the sun along the year – necessary for the determination of latitude on board.

The text contains the rules for use, framed in rectangular boxes, and numerical tables with the values of declination for the months of the year. It’s an uncommon design, where both the rules and the tables are adorned with numerous iconographic elements which provide an unexpected liveliness to the whole document.

Manuscripts such as this, collecting the technical information and tables necessary to calculate latitude or aid navigation, were common in the 16th century.