Draft:Systema Saturnium

Systema Saturnium

Title page of the first edition.
Author	Christiaan Huygens
Country	Dutch Republic
Language	Latin
Subject	Astronomy
Publication date	July, 1659

Systema Saturnium (System of Saturn) is an astronomical treatise published in Latin by the Dutch scientist Christiaan Huygens on July, 1659. Considered the most significant work on telescopic astronomy since Galileo's half a century earlier, Systema Saturnium recounts Huygens' discovery of Saturn's moon, Titan, and offers an explanation for Saturn's strange appearance in the form of a surrounding ring. Huygens additionally introduced the concept of the micrometer and outlined a method to measure the angular diameters of planets.

Systema Saturnium is also known for his cosmological component. The previous scheme on sizes and distances of the Sun, Moon, and planets dating back to Ptolemy have been largely abandoned due to increasing acceptance of Copernicus' work and the invention of the telescope. However, there was no consensus regarding the actual values as previous methods, such as Hipparchus' eclipse method and Aristarchus' lunar dichotomies, yielded conflicting results. Huygens rejected both methods, choosing instead an argument from harmony where the Earth's size is intermediate between Venus and Mars, with a diameter 1/111th of the Sun and a solar distance of 25,086 terrestrial radii. These were the estimates closest to the modern values until the Venus observations that took place more than a century later.

Overview

In 1654, after publishing his mathematical work De Circuli Magnitudine Inventa, Huygens turned his attention to astronomy and devoted his time to both the technical and observational aspects of the discipline. After soliciting advice regarding lens-grinding from the best craftsmen in Europe, he and his brother Constantijn Jr. were able to design telescopes for astronomical research. On March 25, 1655, Huygens began following a small star in the vicinity of Saturn, and within three months Huygens established the period of revolution for this object. He sent an anagram to John Wallis at Oxford and Gottfried Aloys Kinner in Prague with the following words:

Ad movere oculis distantia sidera nostris, vwwwcccrrhnbqx

The Latin translates to "To move the distance of our eyes to the stars." Such anagrams were used at the time to make priority claims, as numerous astronomers were simultaneously observing Saturn, and Huygens felt both pressure to announce his discoveries and concern over the compromises a publication entailed. When Saturn reappeared in January 1656, he was able to use a refracting telescope with a 43x magnification of his own design to further confirm his discovery of Saturn's first moon, today known as Titan. Huygens published a short pamphlet on the matter a few months later entitled De Saturni Luna, where he also announced he had solve what causes the strange appearance of Saturn, which have baffled astronomers, and promised a full system of the planet in short order with another anagram:

aaaaaaacccccdeeeeehiiiiiiillllmmnnntmnniuiooooppqrrstttttuuuuu

Contents

Saturn's changing appearance alongside a picture of Saturn's rings at their greatest inclination.

Huygens's drawing of a nebula.

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Reception

Systema Saturnium is considered the most important work on telescopic astronomy since Galileo's Sidereus Nuncius fifty years earlier. Huygens' astrometric techniques and his conception of the micrometer finally allowed the telescope to be used as an instrument to measure (rather than just sighting) astronomical objects.