The original image of this sidereal calendar is taken from the 'Astronomicum Cæsareum’ by Petrus Apianus. Published in 1540 and dedicated to Holy Roman Emperor, Charles V and his brother King Ferdinand I. The book is an early astronomical treatise and is marked by its particular use of the volvella, a circular paper slide chart with movable parts. The volvella’s served early academics as a primitive form of computational device which allowed the user, as in the case of this designs origin, a means of working out dates and the positions of constellations and by extrapolation telling sidereal time.
Sidereal time in a form of timekeeping used by astronomers to track the movement of heavenly bodies and easily find them, interestingly a day in sidereal time is about 4 minutes shorter than our more commonly used heliocentric form of timekeeping. 
This calendar has been recovered from public domain archives and reinterpreted by the artist with hand gilded 24kt gold leaf and modern water based screen printing in order to share and encourage people to revisit this beautiful piece of our history.