A masterpiece from the Golden Age of celestial cartography

Andreas Cellarius. Harmonia Macrocosmica of 1660

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From the dawn of humanity, the motions of the Sun, the Moon and the heavens must have incited people to admiration and study. The Sun and the Moon, the quintessential embodiments of day and night, already determined from very early on - long before the invention of writing - the three primary divisions of every calendar: the day, the month and the year. The constellations must also have been used for the regulation of the calendar at a very early stage in human history. The course of the Moon and its phases can be determined by simple observation, but the Sun's course across the heavens is obscured by the fact that sunlight overpowers the light of the stars that lie behind it. It is possible, however, to determine the position of the Sun in the celestial hemisphere by approximation, using those bright stars which rise in the east just before sunrise or set in the west just after sunset. In many ancient cultures, the most important moments in the agricultural year - for example, when it was time to sow or harvest - were indicated by the heliacal rising or setting of prominent stars or constellations. In the same way, the calendar - usually based on twelve months of 29 or 30 days that followed the phases of the Moon - was made to harmonize with the solar year of approximately 365 days by adding an intercalary month every couple of years.

The scientific description of the heavens

We owe the first scientific description of the heavens to the Greek astronomer Hipparchus of Nicaea, who was active on the island of Rhodes around 135 BC. According to a later tradition, the appearance of a new star - a nova or a comet - in the sky was supposedly the reason behind Hipparchus' decision to make a survey of the heavens. His original star catalogue has not survived, but can be substantially reconstructed from the surviving works of the Greek astronomer Claudius Ptolemy, who lived in Alexandria around AD 150. In his 13-volume Great mathematical handbook, later known as the Almagest, Ptolemy provides detailed instructions on how to calculate the positions of the Sun, Moon and planets along with an adapted version of Hipparchus' star catalogue. Ptolemy lists some 1,028 stars (with three duplicates), arranged in 48 separate constellations.

Ptolemy's world system

In addition to describing the constellations, the Almagest provides detailed information on calculating the positions of the Sun, the Moon and the planets. Ptolemy thereby proceeds from a geocentric worldview, according to which the Earth occupies a central, fixed position and the heavenly bodies revolve in circular motions around it. Since observations had already revealed that the Sun, Moon and planets did not revolve around the Earth at a uniform velocity, Ptolemy had to take refuge in a more complicated theory, developed around 200 BC by the Greek mathematician Apollonius of Perga, according to which the movements of the heavenly bodies were explained by a combination of two or more circular motions. Nevertheless Ptolemy's treatises would continue to exercise a great deal of influence on later Islamic and European astronomers. His scheme for the distances and dimensions of the heavenly bodies would be followed almost without alteration until the late of the 16th century.

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The planisphere of Tycho Brahe drawn in a planar view
The northern stella hemisphere with the terrestial hemisphere lying between