On Jan. 14, 2005 the Huygens Titan probe began its dramatic plunge through that moon's murky atmosphere having left the Cassini mother ship on December 27, 2004. After a short 2-1/2 hour descent it landed on the surface. It took the combined Cassini-Huygens craft quite a long time to get to this point having left Cape Canaveral Air Force Station, Florida on October 15, 1997.

We have become pretty nonchalant about these absolutely spectacular engineering achievements in space like this one, which is reminiscent of hitting the period at the end of this sentence over a 100 meter distance with a dart. It is in fact a phenominal accomplishment especially if you factor in the unbelievably cold temperatures of outer space. To Cassini and Huygens it would have been incredible.

Giovanni Domenico Cassini
Both Giovanni Domenico Cassini and Christiaan Huygens studied Saturn and her moons during the latter half of the 17th Century. Huygens spotted the first moon, Titan, orbiting Saturn in 1655 and then Cassini found four more (Iapetus in 1671, Rhea in 1672, Tethys in 1684, and Dione in 1684). He also discovered the gap in the ring system of Saturn now known as the Cassini division in 1675.

Both men lived and worked in the 17th Century¹ during about the same time as Isaac Newton. Cassini was born in Perinaldo, Genoa in the Tuscany region of Italy on June 8, 1625. After being educated in various institutions, he was offered a position in the newly constructed Panzano Observatory in Bologna. Ironically his knowledge about astonomy had come from an early interest in astrology.

He later became professor of mathematics and astronomy at the University of Bologna. His expertise also covered many areas other than astronomy. He was an expert in hydraulics and engineering and was consulted as such. Being a devout Catholic, he was highly regarded in Rome and often consulted by Alexander VII, the Pope at the time.

In spite of his work in astronomy, he was very much inclined to the earth-centered theory of the Universe which was still the official view of the Church. In fact he never completely embraced the Copernican-Newtonian view accepting instead the modified version suggested by Tycho Brahe².

Beginning in 1664 he gained access to a series of greatly improved telecopes. With these, he was able to study Jupiter and her moons in much greater detail than before as well as the planet Mars. This led him to a number of significant new discoveries. Included in these were some, relating to the speed of light which he rejected because they were at odds with his beliefs.

His brilliant discoveries gave him an international reputation and led to his being invited to Paris in 1668. There he was asked to oversee the construction of the Paris Observatory and upon its completion was given the post of it's new head in 1671. He finally decided that his move to Paris had been more than temporary and he became a French citizen changing his name to Jean-Dominique Cassini. He ran the observatory until after 1700 when he was succeeded by his son Jacques Cassini (1677-1756).

In fact the running of the observatory passed from one Cassini to the next until Jacques Cassini's son, Jean-Dominique Cassini (1748-1845) lost the post in 1793. All the Cassini's made many contributions to astronomy and related fields. Cassini pere, continued to make many more important discoveries including that Cassini division in the rings of Saturn as well as those four moons. For a more complete history you might want to visit this website.

Christiaan Huygens
The Cassini division is a gap in the ring system of Saturn. This ring system was first detected by Christiaan Huygens. Huygens was born in 14 April 1629 in The Hague, The Netherlands. His father Constantijn Huygens had studied natural philosophy and was a diplomat. It was through him that Christiaan was to gain access to the top scientific circles of the times. In particular Constantijn had many contacts in England and corresponded regularly with Marin Mersenne and was a friend of Descartes.

To give you a sense of these connections, Marin Mersenne was a pivotal figure in the lives of the likes of Fermat, Pascal, Gassendi, Roberval, Beaugrand and others who later became the core of the French Academy of Sciences. Such was young Christiaan's stature in the scientific community of his day that the French King, Louis XIV, invited him to Paris to take on the leadership of this same scientific academy.

This was all the more remarkable considering the pervasive roman catholicism of France during this time when Huygen's native Holland was staunchly Protestant. Even when the French King declared war on the United Dutch Provinces in 1672, Huygens was still welcomed with open arms. This did not last however and by the 1680's the climate in France became less tolerant and the freedom of religion of the Protestants became progressively more restricted. Because of this Huygens, who had been home in The Hague because of illness since 1681, decided not to return to Paris.

In addition to much and varied tutoring, Christiaan studied law and mathematics at the University of Leiden from 1645 until 1647 beginning a career that placed him squarely in the realm of major thinkers on a par with Newton, Descartes and Galileo. Aside from such practical accomplishments as a highly accurate pendulum clock movement, superior lenses and telescopes, exploring the rings of Saturn and other celestial bodies, Huygens was first and foremost a brilliant thinker.

He was one of the first to apply mathematics to the study of nature. In the 17th century this was a novel, even revolutionary idea. Up to that time the physical world, for example the elements, earth, water, air, and fire were described rather than analyzed. Taking a cue from Rene Descartes, a friend of the Huygens family, young Christiaan concluded that nature could be described in mathematical terms.

What this really meant was that for the first time nature was seen to have a system which could be analyzed and understood. The ramifications of that thought can best be appreciated if you remember that for all his brilliance, Descartes himself was still somewhat intimidated by the church-sanctioned Aristotelianism that prevailed in his day.

Evidently not too concerned about this, Huygens tossed the fat in the fire and in effect proclaimed a new approach to science which coincided with the empiricism of John Locke. These were catalysts that led directly to many of the discoveries and scientific insights that followed. At a stroke Aristotelian methodology was turned on its head.

The Light of Understanding
One of the areas that caught his interest was the behavior of light. Not entirely unreasonable given the time he spent fooling around with lenses and telescopes. This led him in 1678 to formulate a theory of light which assumed light acted like a wave. Huygens argued that light behaved as if it were a wave propagating through a vacuum, like an ocean wave moving through the sea.

He felt this could best explain reflection, refraction, and especially diffraction—that bent stick in the water trick. This wave theory was further strenghtened by the likes of Thomas Young who in 1801, would show conclusively that light does, in fact, act like a wave by using another property predicted by Huygen's wave model of light, interference.

In spite of the evidence, a competing view, that of light being made of particles, was championed by none other than Isaac Newton who, in 1704, proposed a particle model for light. Because of Newton's stature, Huygen's view was pretty much ignored. It wasn't until 1905, that Albert Einstein would finally complete the picture. Combining Huygen's wave model and Newton's particle view, he was able to explain another phenomenon, the photoelectric effect.

In one final act of defiance in 1690, Huygens published The Celestial Worlds Discover'd: Conjectures Concerning the Inhabitants, Plants, and Productions of the Worlds in the Planets. In this extraordinary book he suggested that the Universe be populated with "...so many Suns, so many Earths ...And how must our Wonder and Admiration be increased when we consider the prodigious Distance and Multitude of the Stars."

This in a world that had barely got used to the idea that the earth was not the center of the universe. Yes, Christiaan Huygens was quite a fascinating character. He was one of the last great polymaths with his fingers in many different pies. There are many sites including this one where you can learn more about this brilliant revolutionary who is at last getting some much deserved recognition.

All this, thanks to a clever little space probe that now rests on the "muddy" shore on a far-away Saturnian moon.

• Christiaan Huygens (1629-1695)

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