|Compilation from Huygen's Systema Saturnium (1659) |
showing how Saturn's appearance had changed from
1610 to 1646.
|Huygens' diagram of a ring cycle from his Systema Saturnium.|
Almost half a century passed before Christiaan Huygens (1629-1695), at the age of only 26, solved 'the Saturn problem.' Alexander's book describes Huygens' discovery of Titan, in March 1655, and how repeated observations between 1656 and 1659 (as Saturn's northern hemisphere was emerging into spring sunlight) confirmed his theory that the two ansae were indeed the broad flat ring that we now know and love. His Systema Saturnium was published in 1659, and suggested that the rings were inclined by more than 20 degrees to the ecliptic, explaining the variations that observers had witnessed over the past 50 years.
|Robert Hooke's observation of Saturn |
from June 1666, published in the first
volume of the Philosophical Transactions.
A Late Observation about Saturn made by the Same (Mr. Hooke)
June 26 1666 between 11 and 12 at night I observed the body of Saturn through a 60 foot telescope and found it exactly of the shape represented in the figure. The ring appeared of a somewhat brighter light than the body, and the black lines crossing the ring and crossing the body (whether shadows or not, I dispute not) were plainly visible whence I could manifestly see, that the southernmost part of the ring was on this side of the body, and the northern part behind, or covered by the body.
[Incidentally, Hooke had been the assistant to Robert Boyle of Boyle's Law, and they conducted their experiments in an Oxford house now part of my college on the High Street, University College].
John Flamsteed (1646-1719), the first Astronomer Royal, observed Saturn in 1671 very close to the northern autumnal equinox, and found the rings to be 'very slender, and to one that thought not of them, scarce discernable' (volume 6 of Phil. Trans., heliocentric longitude of 180 degrees, northern autumnal equinox two Saturnian years after Galileo had first viewed the planet's disc). This brings us full circle in solving the mystery of Saturn's appendages and up to the time of Jean Dominique Cassini, and his discoveries of Saturn's icy satellites and the division in the rings, subject of a later blog post.
Summary of Saturn Years, Measured from Spring Equinox (Heliocentric Longitude of Zero)
Saturn Year One: 1597-1627: Galileo discovers Saturn's 'strange appendages'.
Saturn Year Two: 1627-1656: Several theories proposed to explain Saturn's servants.
Saturn Year Three: 1656-1685: Huygen's solves the Saturn problem and discovers Titan, Hooke and Flamsteed observe Saturn's ring progression.