Galileo or Huygens? IYA (2009 Jan 01)

[bjmb]

It says in the text accompanying the first APOD of 2009 that "Galileo discovered that [...] Saturn has rings." But wasn't it rather Christian Huygens who first correctly interpreted what to Galileo had remained a mystery? I quote from the ESA website: "Although he saw the rings first, Galileo did not know what they were. They appeared to him as 'ears' or lobes either side of the planet. It was Christaan [sic] Huygens who first proposed that Saturn was surrounded by a solid ring in 1655."
I wish every stargazer a happy 2009 - BJ Mansvelt Beck, Amsterdam, The Netherlands

[orin stepanek]

http://apod.nasa.gov/apod/ap090101.html Galileo was the first to see them! Huygens than should get credit for Identifying them.

Orin

[neufer]

It says in the text accompanying the first APOD of 2009 that "Galileo discovered that [...] Saturn has rings." But wasn't it rather Christian Huygens who first correctly interpreted what to Galileo had remained a mystery? I quote from the ESA website: "Although he saw the rings first, Galileo did not know what they were. They appeared to him as 'ears' or lobes either side of the planet.

It was Christaan [sic] Huygens who first proposed that Saturn was surrounded by a solid ring in 1655."

So Huygens got it wrong too.
---------------------------------------------
Intersaturnial Ear of Astronomy
..............................................

Historical Background of Saturn's Rings
Written by Ron Baalke

1610 - Galileo Galilei becomes the first to observe Saturn's rings with his 20-power telescope. He thought the rings were "handles" or large moons on either side of the planet. He said "I have observed the highest planet [Saturn] to be tripled-bodied. This is to say that to my very great amazement Saturn was seen to me to be not a single star, but three together, which almost touch each other".


Sketch of Saturn by Galileo in 1610

1612 - Galileo was astounded when he found that the rings he first observed a couple of years earlier had now disappeared. He wrote "I do not know what to say in a case so surprising, so unlooked for and so novel". The rings were, in fact, edge-on from Earth's perspective. Galileo inadvertently became the first person to observe a Saturn ring plane crossing.

1616 - Galileo now observes the rings as two half ellipses. He wrote "The two companions are no longer two small perfectly round globes ... but are present much larger and no longer round ... that is, two half ellipses with two little dark triangles in the middle of the figure and contiguous to the middle globe of Saturn, which is seen, as always, perfectly round".


Sketch of Saturn by Galileo in 1616

1655 - Christaan Huygens proposes that Saturn was surrounded by a solid ring, "a thin, flat ring, nowhere touching, and inclined to the ecliptic." Using a 50 power refractor that he designed himself, Huygens also discovers the first Saturn moon, Titan, just 7 months before the ring plane crossing for that year.


Huygens' Sketch of Saturn in 1655

1656 - Johannes Hevelius postulates that Saturn's rings were two crescents attached to an ellipsoidal central body.

1658 - Christopher Wren argues that an elliptical corona was attached to Saturn, and the planet and corona rotated about the major axis of the corona. He speculated that this corona was so thin that it was invisible when it was edge-on from Earth's perspective.

1659 - Christaan Huygens publishes his book, Systema Saturnium, in which he explains that every 14 to 15 years the Earth passes through the plane of Saturn's ring.

1660 - Jean Chapelain makes an insightful suggestion that Saturn's rings are made up of a large number of very small satellites. Since most astronomers of the time strongly believed that Saturn's ring was solid (with one notable exception: Cassini), Chapelain's suggestion went mostly unnoticed. It would be another 200 years until Maxwell in 1856 makes a similar deduction.

1664 - Giuseppe Campani observes that the outer half of Saturn's ring is less bright than the inner half, but fails to recognize this as being two separate rings.

1671-1672 - Giovanni Cassini discovers two new Saturn moons, Iapetus and Rhea, during the ring plane crossings of 1671-1672. Cassini first observed Iapetus in 1671 on the west side of Saturn, but failed to observe it on the east side in 1672 even though he knew it was there. He correctly postulated that Iapetus had light and dark sides, and it always kept the same face turned to Saturn.

1676 - Giovanni Cassini discovers a gap in the rings which would later be named the Cassini Division. The outer ring would be called the A Ring and the brighter inner ring would be called the B Ring.


Cassini's Sketch of Saturn in 1676 Showing the Gap in the Rings

1684 - Giovanni Cassini discovers two more Saturn moons, Tethys and Dione, just prior to the ring plane crossing of 1685. It would be over 100 years until the next Saturn moon would be discovered.

1780 - William Herschel reports seeing a "black list", or linear markings on one side of the B Ring near its inner edge. He had probably observed what would later be called the Encke Division.

1787 - Pierre de Laplace suggests that Saturn has a large number of solid rings. William Herschel suspects he has observed a new moon of Saturn (which would later turn out to be Enceladus), but waits until the next ring plane crossing in 1789 to pursue it further.

1789 - William Herschel suggests that Saturn is surrounded by two solid rings. Herschel also discovers two new Saturn moons, Enceladus and Mimas, during the ring plane crossing of 1789-1790. Herschel also finds that Saturn is flattened at its poles, something he suspected since 1776. He also makes one of the earliest estimates of the thickness of the rings at 300 miles, and reports observations of eclipses of Saturn's moons by the planet's shadow.

1790 - William Herschel is able to determine the rotation period of Saturn's ring to be 10 hours 32 minutes.

1825 - Henry Kater reports seeing three gaps in the A Ring, but no one else could verify Kater's claim for several years.

1835 - Friedrich Bessel is able to determine the orientation of Saturn's pole with unprecedented accuracy and was able to determine the precession period of the pole at 340,000 years. (The modern estimate is 1.7 millions years).

1837 - Johann Encke observes a dark band in the middle of the A Ring that matches one of the gaps that Kater observed in 1825. This dark band in the A Ring would be later known as Encke's Division, even though Encke never really observed it as a gap in the rings.

1848 - William Bond, George Bond and William Lassell discover a new Saturn moon, Hyperion, during the ring plane crossing of 1848-1849. William Bond and George Bond observe that the unlit side of the rings was barely visible, and infer a ring thickness of 40 miles.

1849 - Edouard Roche suggests that Saturn's ring system was formed when a fluid satellite had approached Saturn so closely that it had been torn apart by tidal forces.

1850 - William Bond and George Bond observe a dark band across Saturn immediately adjacent to the interior edge of the B Ring. Charles Tuttle suggests that this might be caused by a dusky ring inside the B Ring. This ring was intially known as the crepe ring, and later officially became the C Ring. George Bond concludes that a system of narrow solid rings could not be stable and that Saturn's rings had to be fluid.

1852 - Several observers notice that the limbs of Saturn are visible through the C Ring. This observation made it difficult to defend the theory that the rings were solid.

1856 - James Maxwell deduces that the Saturn rings cannot be solid and must be made of "an indefinite number of unconnected particles".

1861-1862 - The dark unlit side of Saturn's rings was observed by James Carpenter, William Wray and Otto Struve.

1866 - Daniel Kirkwood notices that a particle in the Cassini Division would be in 3:1 resonance with the peroid of Enceladus.

1872 - Daniel Kirkwood is able to associate the Cassini Division and Encke's Division with resonances of the four then known interior moons: Mimas, Enceladus, Tethys and Dione.

1876 - Spectacular white spots are observed on Saturn by Asaph Hall.

1883 - The first photograph of Saturn's rings is taken by Commons.


The First Photograph of Saturn by Commons, 1883

1888 - James Keeler becomes the first person to clearly observe the Encke Division (Encke only saw it as a dark band in 1837).

1889 - Edward Barnard observes an eclipse of Iapetus by Saturn's rings. Watching Iapetus become dimmer going through the shadow of the C Ring and disappear completely in the shadow of the B Ring, Barnard concludes that the C Ring must be semitransparent and that the B Ring is opaque.

1895 - James Keeler and William Campbell observe that the inner part of the rings orbit more rapidly than the outer part of the rings, confirming Maxwell's deduction in 1856 that Saturn's rings were made up of small particles.

1898 - William Pickering discovers a new Saturn moon, Phoebe. This is the first and only Saturn moon discovered from ground based observations that was *not* around the time of a ring plane crossing.

[Donald Pelletier]

Replacing the discovery of Saturn's ring by the observation of sunspot will be the exact list of what we reed in introductory textbook. This link is a good source : http://www.astro.umontreal.ca/~paulchar ... ers_e.html

[neufer]

Replacing the discovery of Saturn's ring by the observation of sunspot will be the exact list of what we reed in introductory textbook.

This link is a good source : http://www.astro.umontreal.ca/~paulchar ... ers_e.html

Now you are going to have the Fabricius Family mad at you!

Title page of the small pamphlet published in 1611 by Johann Goldsmid, better known by his latinized name Fabricius.

[Johann Fabricius (1564-1617)] was born on 8 January 1587 at Resterhave, in East Frisia (Northwestern Germany). His father was David Fabricius (1564-1617), a Lutheran pastor, astrologer and able astronomer who in 1596 discovered the variability of the star Mira Ceti. Between 1604 and 1610 Fabricius the son studied medicine first at Helmstedt, then Wittenberg, then at Leyden where he first engaged in telescopic observations. He first saw sunspost on 27 February 1611, (9 March on the Gregorian calendar, not yet adopted in East Frisia) and shortly thereafter teamed up with his father for further observations.

The Fabricius correctly interpreted the day-to-day motion of sunspots as an indication of the Sun's axial rotation, and the young Fabricius completed in June of the same year a short account of their observations and interpretation, which was published in June 1611 under the title de Maculis in Sole observatis et apparente earum cum Sole conversione, Narratio (``Account of Spots observed on the Sun and of their apparent rotation with the Sun''), and was sold at the Frankfurt book fair the following autumn.

Like Thomas Harriot, the Fabricius son-father team first observed sunspots directly through their telescope shortly after sunrise or before sunset. Their harrowing account of their observations is worth quoting: (excerpt from the translation in the paper by Mitchell cited below):

"... Having adjusted the telescope, we allowed the sun's rays to enter it, at first from the edge only, gradually approaching the center, until our eyes were accustomed to the force of the rays and we could observe the whole body of the sun. We then saw more distinctly and surely the things I have described [sunspots]. Meanwhile clouds interfered, and also the sun hastening to the meridian destroyed our hopes of longer observations; for indeed it was to be feared that an indiscreet examination of a lower sun would cause great injury to the eyes, for even the weaker rays of the setting or rising sun often inflame the eye with a strange redness, which may last for two days, not without affecting the appearance of objects."

They soon adopted instead Kepler's camera obscura technique, where an image of the Sun is formed through a pinhole opening in a darkened room and observed in projection.

. Hamlet > Act I, scene II
.
KING CLAUDIUS: How is it that the clouds still hang on you?
.
HAMLET: Not so, my lord; I am too much i' the sun.
..........
KING CLAUDIUS: For your intent
. In going back to school in Wittenberg,
. It is most retrograde to our desire:
. And we beseech you, bend you to remain
. Here, in the cheer and comfort of our eye,
. Our chiefest courtier, cousin, and our son.

QUEEN GERTRUDE: Let not thy mother lose her prayers, Hamlet:
. I pray thee, stay with us; go not to Wittenberg.
..........................................
. Act II, scene II
.
HAMLET: For if the sun breed maggots in a dead dog,
-----------------------------------------------------------
By January 1638 GALILEO is totally Blind.
On September 1640 John MILTON visits GALILEO.
.
<<John MILTON(1608-1674) called on the Blind GALILEO in Arcetri
near Florence where the astronomer had been confined by papal order.
Then, in his Areopagitica (1644) MILTON described GALILEO as a
heroic victim: "This was it which had damped the glory of Italian wits
nothing had been there written now these many years but flattery
and fustian.">> - The Discoverers Daniel Boorstin
.........................................................................
<<Although MILTON's regular official duties of translation and
writing seem to have been rather multifarious than hard, they were,
in themselves, not good for a man with very weak eyesight; and his
unfortunate aptitude for pamphleteering marked him out for overtime
work, which was still worse. The last stroke was believed by himself,
as a famous boast records, to have been given by his reply to
Salmasius's Defensio Regia. [By 1652, MILTON, himself,
was totally Blind. >> - http://www.bartleby.com/217/0504.html
---------------------------------------------------

Johann Fabricius died on 19 March 1616, and his father, who did not pursue sunspot observations,
was killed the following year by an enraged parsoner he had attacked from the pulpit over a stolen goose.

Contemporarie such as Kepler, Simon Marius, and Maestlin were aware of the Fabricius' early sunspot work, and Kepler in particular repeatedly refers to it in various of his writings. However, the priority controversy between Galileo and Scheiner took center stage and the contribution of the Fabricius was all but forgotten until a hundred years later, when a copy of Fabricius' small pamphlet was rediscovered and publicized in 1723.>>

http://www.astro.umontreal.ca/~paulchar ... ius_e.html

[apodman]

Galileo ... Huygens ... Hevelius ... Cassini ... Herschel ... Laplace ... Bessel ... Encke ... Roche ... Maxwell ...
Pickering

That's only half of neufer's list, and a lot of familiar names. Apparently a lot of people took an active interest in Saturn. Seeing Saturn's rings for the first time is still a thrill today, even though it has been done before. With a chart to tell you where to look, Titan is also in reach for back yard observers. Who gets more first time visitors, Saturn (by telescope) or the Grand Canyon (in person)?

For useful insight in the understanding of Saturn's rings, my MVP vote goes to Roche.