The Eighth Continent

The 8th Continent : Looking at the Moon in Early Modern Europe.


John Wilkins, Discovery of a New World on the Moon, London, 1684 ed., Frontispiece.


Why were lunar maps revolutionary in the 17th century? Before telescopes came onto the European market in 1609 images of the Moon, if depicted at all, were plain. The Moon was considered to be a perfect sphere and darker spots, visible to the naked eye, were explained as variations in density. From 1609 telescopes revealed the mountainous peaks and craters on the Moon. Some, such as John Wilkins [See the November Book of the Month], believed the Moon was another habitable world like Earth. 21st century enthusiasts have revived the idea of Lunar habitation and refer to the Moon as the 8th continent. This exhibition displays the earliest maps of the Moon drawn with the aid of telescopes.


John Wilkins, Mathematical Magick, 1691 ed. Portrait.

The importance of the idea that the moon was perfectly spherical cannot be underestimated. It was connected to the Aristotelian and Ptolemaic foundation of knowledge about the nature of the universe, a paradigm in place for one and half millennia, and on the brink of collapse in 1609. Furthermore these theories were integrated into the teaching of the Catholic Church by Thomas Aquinas in the 13th century meaning their collapse would have religious consequences.

In the 4th Century BCE Aristotle laid out his views on the structure of the universe. In this universe there was a strict order and everything had its natural place. The Earth was the centre of this universe. It was believed to be the heaviest of all the bodies and it was also seen as the most imperfect part of the universe. The Moon and all beyond it were considered perfect and unchanging. The heavenly orbs were thought to be composed of perfect spherical shells of aether and the moving bodies rotated around Earth in perfect circles. In the Aristotelian system the Earth and its immediate surrounds were made up of four elements earth, water, air, fire. Earth sought to rest closest to the centre, then water, air and fire. The Earth was imperfect however so there were overlaps occasionally where land rose above the level of water. Everything within the sphere of the Earth had its natural place according to their elemental properties under Aristotle’s rules. The only change to these rules were made by Ptolemy in the 2nd century AD. Ptolemy reconciled the observed retrograde movement of the planets with Aristotle’s theories by adding epicycles to the circular orbits while maintaining the integrity of the geocentric Universe. Aristotle’s hierarchical system remained untouched. Until telescopes increased the power and number of observations that could be made the Aristotelian and Ptolemaic systems sufficiently explained the heavens to the level of complexity that they could be analysed.

In The Structure of Scientific Revolutions Thomas Kuhn described a series of puzzles, inconsistent with the existing world view, which reach a critical mass and result in a crisis before a shift in scientific paradigm occurs. Telescopic observations of the Moon were puzzles which astronomers found difficult to reconcile with the Ptolemaic and Aristotelian framework. Further telescopic observations of the Universe revealed further puzzles, irreconcilable with the existing paradigm, which lent credibility to the alternative new Copernican model of the Universe in the eyes of some astronomers. In the 16th century Copernicus, along with a small number of astronomers before him, had the foresight to see the inaccuracies of the Ptolemaic system and the bravery to suggest an alternative but the inconsistencies created by the old system did not reach the critical mass needed to convince other astronomers until the invention of the telescope. Therefore 1609 marked the beginning of a Kuhnian-crisis period in astronomy which led to a paradigm shift from Ptolemaic and Aristotelian to Copernican.


Galileo Galilei, Opere di Galileo Galilei, Florence, 1718. Illustrations of the Moon


In 1609 telescopes became available throughout Europe and allowed astronomers to magnify the Moon. Galileo Galilei improved his telescope from a 3 powered to a 20 powered telescope in a matter of months. His observations showed that the Moon had an uneven surface. This immediately challenged the existing paradigm in three ways.

1. That a celestial body could have a less than perfect surface completely contradicted Aristotle’s outline of the heavens.

2. The Moon’s mountains and valleys similar to those on Earth further contradicted the strict hierarchy of materials which placed Earth at the centre of the Universe because it was made of the heaviest substance.

3.  Finally, if the Moon was composed of mountains and valleys similar to the Earth then the Earth was not unique.

In 1610 he published his observations of our Moon and the moons of Jupiter in Sidereus Nuncius (A Starry Messenger). The moons orbiting Jupiter, similar to our own, further provided evidence that the Earth was not unique but another planet and that Jupiter was a second central point of orbiting motion in the Universe. Galileo used the mounting evidence provided by telescopic observations to support Nicholas Copernicus’ views, published in 1543 in De Revolutionibus, which theorised the Universe revolved around the Sun rather than the Earth.

Galileo followed Sidereus Nuncius with observations of the rings of Saturn, sunspots, and the phases of Venus which all added to the critical mass of puzzles against the existing paradigm. At the same time Johannes Kepler published observations which supported Galileo’s views and improved the Copernican system with calculations that suggested the planets travelled in elliptical pathways. Initially Galileo spoke of these discoveries as theoretical but gradually he declared them to be factual. This threatened not only the existing paradigm but the authority of the Catholic Church who had integrated their own teachings with Aristotle’s. The Catholic Church tolerated Copernican heliocentrism whilst it remained theoretical but once Galileo and others began to affirm the Sun’s place as the centre of the Universe the Vatican condemned these views as heresy and placed Galileo under house arrest in 1633. The Vatican saw Copernicanism as yet another challenge to its authority during a turbulent period of its history. In general, Protestants were more tolerant towards heliocentrism. They lacked a centralised rigid authority and many interpreted the Bible in a way which did not clash with heliocentrism. Thus the Moon and astronomy became embroiled in the religious wars which raged throughout Europe whilst undergoing their own paradigmatic revolution.


Johannes Hevelius, Selenographia, 1647. Full Moon Plate


Johannes Hevelius was a brewer from Gdansk, Poland. The business inherited from his father provided enough wealth for him to indulge his passion for astronomy. Although Galileo was the first to depict telescopic images of the Moon Hevelius was dissatisfied with his efforts to visually depict it. Galileo’s efforts were utilitarian and accompanied the text but Hevelius wanted his illustrations to speak for themselves. In 1647 Hevelius published Selenographia, a detailed atlas of the Moon visually far superior than Galileo’s depictions. Hevelius had enormous talent and made his own lenses, a 12 foot telescope, and drew and engraved the maps himself. Hevelius even built a 150 foot telescope for his later observations.


Johannes Hevelius, Selenographia, 1647. Fig F.


Selenographia was one of the first sophisticated atlases of the Moon to appear in the new age of the telescope and contained 134 illustrations. He observed and depicted the Moon in all phases. Due to the librations (a slight wobble to and fro) of the Moon we observe slightly more than one hemisphere of the Moon. In Selenographia Hevelius translated the three-dimensional lunar surface into a two-dimensional topographical surface and created a composite map where the surfaces of the Moon visible from Earth at different phases were depicted simultaneously. This would be an impossible sight in reality but Hevelius combined areas visible throughout the Moon’s cycle to create a useful visualisation for astronomers. Furthermore he used the same morning illumination for each area of the Moon as the features visible to us on the surface vary throughout the cycle due to the angle of the Sun’s rays. There were some inaccuracies in Hevelius’ depictions but it remains one of the most ambitious projects of that time.


Johannes Hevelius, Selenographia, 1647. Phases of the Moon.


Hevelius also named areas of the Moon after places on Earth. This showed his support for the theory that the Moon was a world similar to Earth and for the Copernican theory of the heliocentric Universe. Hevelius’ nomenclature was not ultimately adapted however. The names Hevelius chose were not easily relatable to their corresponding locations on Earth. They ultimately proved less appealing than the nomenclature chosen by Giovanni Batista Riccioli and Francesco Maria Grimaldi in 1651. Hence in July 1969, Apollo 11 landed in The Sea of Tranquility rather than Euxine sea.


Giovanni Battista Riccioli, Algamestum Novum 1651. Francesco Maria Grimaldi’s Lunar Map


In1651 Jesuit priest Giovanni Battista Riccioli published a book titled Algamestum Novum , which dealt with various aspects of astronomy. Riccioli worked with another Jesuit, Francesco Maria Grimaldi, to draw the maps of the Moon included within its pages. By this time, the Vatican had accepted that Aristotle’s perfect spherical orbs were a fallacy while still maintaining that the Earth, not the Sun, was the centre of the Universe. Riccioli and Grimaldi were therefore free to map the Moon’s uneven surface. They combined the most accurate features of Hevelius’ (1947) and Michael Florent van Langren’s (1945) lunar maps. This made their version the most accurate map of the Moon in the mid-seventeenth century and this increased its circulation beyond the Catholic world and into Protestant libraries such as Edward Worth’s.


Francesco Maria Grimaldi’s Nomenclature Map


As Catholics, Riccioli and Grimaldi rejected Copernicus’ heliocentric model of the Universe and Hevelius’ Earth-like nomenclature for the areas of the Moon because they negated the Earth’s uniqueness and jeopardized the authority of the church who supported geo-centrism. On the other hand, Riccioli did acknowledge Copernicus, Kepler, Galileo and other earlier astronomers who supported heliocentrism by naming telescopic spots (craters seen only through telescopes) after them. Their craters however were described by Riccioli as floating islands and were aptly situated in an area named the Sea of Storms. The location is indicative of the Vatican’s attitude towards the problems their heretical views caused. However, historian Ewan A. Whittaker suggested that Riccioli was secretly a supporter of heliocentrism and included them for future generations. Riccioli named other areas of the moon visible to the naked eye; Sea of Tranquility; Sea of Serenity; Lake of Dreams; and Sea of Crises; Sea of Rain etc. The upper half contained telescopic spots named after ancient philosophers and astronomers and the lower half was sectioned off and named after modern astronomers. Despite being on the losing side of the battle between heliocentrism and geocentrism, Riccioli’s nomenclature of the Moon prevailed due to the accuracy of the map and the appealing mix of abstract and personifying designations.


This online exhibition was curated by Neasa McGarrigle, B.A. (TCD), M.Sc. (Oxon); Candidate for Ph.D, Trinity College Dublin.


To learn more about the history of astronomy please visit the Worth Library online exhibition ‘Astronomy at the Worth Library’:



Giovanni Batistia Riccioli, Algamestum Novum, Bologna, 1651.

Johnannes Hevelius, Selenographia, Gdansk, 1647.

Galileo Galilei, Opere di Galileo Galilei, Florence, 1718.

John Wilkins, A Discovery of a New World, London, 1684 (4th ed.).


The Galileo Project, Rice University:

Charles Coulston Gillispie (ed.), Dictionary of Scientific Biography, (New York, 1970-80).

Edward Grant, ‘In Defense of the Earth’s Centrality and Immobility: Scholastic Reaction to Copernicanism in the Seventeenth Century’ in Transactions of the American Philosophical Society, New Series, Vol. 74, No. 4 (1984), pp.1-69.

Michael Hoskin (ed.), The Cambridge Concise History of Astronomy, (Cambridge, 1999).

Thomas Kuhn, The Structure of Scientific Revolutions, (Chicago, 2012, 50th anniversary edition).

Mary G. Winkler and Albert Van Helden, ‘Representing the Heavens: Galileo and Visual Astronomy’ in Isis, Vol. 83, No. 2 (Jun., 1992), pp. 195-217.

Ewen A. Whittaker, Mapping and Naming the Moon; a history of lunar cartography and nomenclature, (Cambridge 2009).


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