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camdigger
08-18-2009, 12:16 PM
It probably old news to those stargazers on board here, but the spring 09 issue of Invention and Technology magazine has an article on Gallileo Galilei. In the article, it says Gallileo's telescope is on display in a display at the Franklin Institute celebrating the 400th anniversary of its discovery.

lazlo
08-18-2009, 12:28 PM
Pretty neat, but it's a common misconception that Gallileo invented the telescope. They were invented in the Netherlands in 1608, by either Hans Lipperhey or Jacob Metius (the Hague awarded a joint patent to both), and by 1609 you could buy a telescope in many spectacle-maker's shops in Europe.

Thomas Harriot published a paper about observing the Moon with a six-powered instrument in early 1609.

Gallileo built his first (3 power) telescope in late 1609, and with a later 20 power version he built in 1610, he famously observed the moons of Jupiter. By the way, that 20 power telescope is the one he presented to the Vatican, that eventually got him into a lot of trouble...

I'm guessing the Franklin Institute has the 20 power telescope? I'd love to see that!

Evan
08-18-2009, 12:44 PM
It wasn't Galileo's telescope that got him in trouble, it was his belief that the Earth wasn't the centre of the universe. If the Earth wasn't the centre it diminished it's importance as a creation of God and the church of the day wouldn't stand for that. His telescope merely allowed him to observe that the moons of Jupiter circled Jupiter and not the Earth. It only takes a single piece of evidence to falsify a theory and that was it. Since Galileo was well known and had published his observations the Church tried to make him recant and republish claiming he was mistaken. He refused.

Incidentally, there is evidence of ground lenses far earlier. A ground quartz lens was discovered in the ruins of Nineveh which places that invention to at least 700BC.

lazlo
08-18-2009, 12:51 PM
Incidentally, there is evidence of ground lenses far earlier. A ground quartz lens was discovered in the ruins of Nineveh which places that invention to at least 700BC.

Right, the Dutch were just the first to realize that you could put two of them in a tube and see things far away :)

camdigger
08-18-2009, 12:59 PM
I would have expected Steven Hawking (the article's author) to have his facts right....

Bruce Griffing
08-18-2009, 01:16 PM
I saw the telescope in the science museum in Florence a few years ago. Having studied physics, it was interesting to feel, for a moment, connected to Galileo. Quite the historical figure in celestial mechanics. BTW, Florence is one of the most, if not the most, interesting cities I have ever visited.

camdigger
08-18-2009, 01:23 PM
It wasn't Galileo's telescope that got him in trouble, it was his belief that the Earth wasn't the centre of the universe. If the Earth wasn't the centre it diminished it's importance as a creation of God and the church of the day wouldn't stand for that. His telescope merely allowed him to observe that the moons of Jupiter circled Jupiter and not the Earth. It only takes a single piece of evidence to falsify a theory and that was it. Since Galileo was well known and had published his observations the Church tried to make him recant and republish claiming he was mistaken. He refused.
.

Gallileo's story highlights some of the challenges facing early scientists. Not only did the church take offense to Gallileo's claims that the universe didn't turn around the earth, but they were P.O. ed that he'd published in the local language rather than the mandated Latin. That meant that the general populace had the info at almost the same time the church did. That meant the church wasn't able to control/prevent the release of a theory that was at odds with the Aristotlelian theory the church subscribed to.

FWIW, I've heard from others sources a well as Steven Hawking's article that the Inquisitors did finally get Gallileo to recant and agree to stop championing Copernican theory. That spared him his life, but still landed him in house arrest for the remainder of his life when he published a "Dialogue Concerning the Two Chief World Systems". This later publication, although as non biased as he could make it, was deemed to have contravened the earlier ban on further discussions or writings on the subject and earned him house arrest for life.
A book he penned while under house arrest "Two New Sciences" leads some to credit Gallileo with being very important in the evolution of the science of Physics.

It would be neat to see Gallileo's telescope.....

Barrington
08-18-2009, 01:46 PM
I would have expected Steven Hawking (the article's author) to have his facts right....To be fair I don't think it was Prof. Hawking's mistake - the assertions that Gallileo invented/built the world's first telescope was in the 'Editors Letter' and repeated in a sidebar which I don't think was his part of his text.

For those interested the article is here:-
http://www2.fi.edu/press/news/2009.spring.invent.pdf

Cheers
.

rantbot
08-18-2009, 02:24 PM
In Sidereus Nuncius (March 1610), Galileo specifically describes (albeit very briefly) three instruments - his first effort, cobbled together from standard spectacle lenses, of about 3x; his second, of about 8x (this is the one he presented to the Senate of Venice), and his (up until the time of writing) most powerful instrument, of about 33x. Nowhere in Sidereus Nuncius does he say what instrument was used to make which observations. He does describe some of the properties of telescopes needed to duplicate his observations. The description seems to be of an instrument of about 20x.

Sidereus Nuncius is not the only available documentation. A letter dated Jan 7, 1610, exists in two incomplete copies. In it, G. describes the observations which led him to the conclusion that the new stars around Jupiter were moons. From the description, this was probably a 20x instrument - one with an objective lens showing fairly severe astigmatism, as is clear from G.'s description of how to minimize the effects with an elliptical stop or diaphragm. G. seems to have believed at the time that it was a general property of refractors, and not due to aspheric errors in his lens.

Now the three surviving telescopes (or lenses) attributed to Galileo himself, all in the museum in Florence, do not show this astigmatism. From this it seems clear that none are the ones he used to discover the "Midicean stars." What happened to his earliest telescopes is hard to say. From surviving letters it's clear that at least one was definitely given to a private secretary of the Grand Duke Cosimo de' Medici. There is no real evidence to identify this telescope as being one of those in the Medici collection (the ones now in the Museo di Storia della Scienza in Florence). One of the Museum's holdings is a separate lens mounted in a plaque carrying an inscription stating that it is the lens of the telescope used to discover the Jovian moons, but the plaque dates from about a century after the event. The lens, though now broken, was tested in 1923, and again in 1992, and is not notably astigmatic. So it is surely not the one referred to in the Jan 7 letter.

Galileo wrote of making "hundreds" of telescopes, while complaining that only a few of those were of the quality necessary to show the things he had claimed in Sidereus Nuncius (lunar mountains, new stars visible in familiar constellations, the Jovian moons - the phases of Venus, and sunspots, were not announced in Sidereus Nuncius). Where did they all go?

Sidereus Nuncius, both the original March 1610 edition and a slightly later "Frankfurt" edition, are available as facsimile images online. There are three English translations, all pretty decent. Very interesting reading - in few scientific works is the excitement of, basically, the discovery of the universe so tangible.

lazlo
08-18-2009, 02:29 PM
I've heard from others sources a well as Steven Hawking's article that the Inquisitors did finally get Gallileo to recant and agree to stop championing Copernican theory. That spared him his life, but still landed him in house arrest for the remainder of his life when he published a "Dialogue Concerning the Two Chief World Systems".

That's right -- Gallileo was openly Heliocentric, until Rome threatened him with the Inquisition. He was then silent on the topic for the next 16 years.

The problem was that he was close friends with a Cardinal who was then elected Pope. Gallileo thought that meant that he had more leeway in the matter, and after appealing repeatedly to the new Pope to publish his views, the Pope suggested that he write a book with three hypothetical views: the Heliocentric view, the traditional Corpernican view, and the Vatican's view.

Gallileo ended up writing "The Dialogue Concerning the Two Chief World Systems" as a debate between two philosophers and a layman, and the Corperican philosopher was called "Simplicio" -- and basically written as a fool. Not exactly a smart think to do for such a brilliant scientist.

He was then tried and convicted of heresy, and spent the rest of his life under house arrest. It would have been much, much worse for him if he wasn't the Pope's friend...

"He set the earth on its foundations; it can never be moved."
Psalm 104:5

rantbot
08-18-2009, 02:32 PM
I'm guessing the Franklin Institute has the 20 power telescope? I'd love to see that!
There's a big website about the Franklin Institute copy. The site moves around a bit, so links are problematical. Try starting here -
http://galileotelescope.org/

As I discussed above, I don't believe that the 20x copies (at the Franklin Institute or the science museum in Kensington, the copy usually seen in astronomy books) have much to do with the telescope Galileo used for his Jovian observations.

lazlo
08-18-2009, 02:33 PM
Now the three surviving telescopes (or lenses) attributed to Galileo himself, all in the museum in Florence, do not show this astigmatism. From this it seems clear that none are the ones he used to discover the "Midicean stars."

Ah, that's tragic. You would think that the telescope survived, no matter who Galileo gave it to -- I wonder if it's in a curator's storage facility somewhere, waiting to be found...

rantbot
08-18-2009, 02:58 PM
Ah, that's tragic. You would think that the telescope survived, no matter who Galileo gave it to -- I wonder if it's in a curator's storage facility somewhere, waiting to be found...
Yes, it's a puzzle. This was big stuff - from England to Denmark to Bohemia to the Vatican (where the Jesuit astronomers were big fans of Galileo's), everybody was fascinated by these discoveries. The instruments were sent, most often via the Florentine court's diplomatic couriers, to much of the royalty of Europe, in the knowledge that once they arrived they would immediately be given to the court mathematicians or astronomers. For a few years, only Galileo's instruments were good enough to show these marvels. The little Flemish novelty telescopes knocked together from eyeglass lenses wouldn't do the job. By mid-century, Galileo's lenses were handily eclipsed by those from Torricelli or Campani (and attribution of those lenses is relatively certain, because they were usually signed on the edges); but for a while, Galileo's telescopes must have been valued just slightly below pieces of the True Cross. It is inconceivable that they would ever have been discarded casually. Yet there are only two telescopes, and one separate lens, nowadays attributed to Galileo. Very peculiar.

Evan
08-18-2009, 06:01 PM
He wouldn't have needed a 20X telescope to see the 4 moons. They are almost visible to the naked eye and his 3X telescope would have been sufficient if he had good vision. Five or six power is plenty and 20 power would probably have had too narrow a field to see them all at once. Telescopes of the day were very long focal length as it minimized abberation and other defects of the lenses. Long focal length means narrow field.

He also lived in a place and time when there was no light pollution at night and being on the coast the air would have been clean as well. Observing conditions would have been free from man made degradation.

camdigger
08-18-2009, 06:21 PM
He wouldn't have needed a 20X telescope to see the 4 moons. They are almost visible to the naked eye and his 3X telescope would have been sufficient if he had good vision. Five or six power is plenty and 20 power would probably have had too narrow a field to see them all at once. Telescopes of the day were very long focal length as it minimized abberation and other defects of the lenses. Long focal length means narrow field.

He also lived in a place and time when there was no light pollution at night and being on the coast the air would have been clean as well. Observing conditions would have been free from man made degradation.

If you know what you're looking for and how/where to find it, it is easy to work with less magnification. Uncertainty as to what he was actually seeing at 3x may have motivated him to pursue higher magnifications. Since the measurements and observations were done without prior knowledge and without photography to do scale overlays etc. to determine motion and hence work back from observed postions, more magnification would be of benefit to make more precise observations, no? Wasn't it about this time or shortly after, the parabolic/elliptical path was documented for later explanation by Johann Kepler and ol' whatsisname...? To determine the difference between a circular orbit and an elliptical orbit with closely spaced focii would require very precise measurements... Pure speculation, but I'm just saying...

rantbot
08-18-2009, 07:28 PM
Wasn't it about this time or shortly after, the parabolic/elliptical path was documented for later explanation by Johann Kepler and ol' whatsisname...? To determine the difference between a circular orbit and an elliptical orbit with closely spaced focii would require very precise measurements... Pure speculation, but I'm just saying...
Tycho, who died in 1601, was the last major astronomer of the pre-telescopic era. Despite the lack of optical aids, his measurements of stellar and planetary positions were remarkably precise. Kepler used them to deduce his laws of planetary motion, hitting on the idea of ellipses about 1605, though his book wasn't published until 1609 - in time to position him in the intellectual landscape of Europe and make him one of Galileo's correspondents. .

Evan
08-18-2009, 07:40 PM
Three times magnification will show the moons clearly. They aren't difficult to see even with no prior knowledge of their existence. Also, the inner moons orbit quickly and he would only need a single night to see what is happening plus a few more to confirm his observations.

Here I have used an observatory program that depicts the apparent size accurately and overlaid it on a photo of the moon at the same scale and apparent brightness in the sky. I also show the configuration of the moons as of 4:30 PDT today and how they will look 12 hours later. The largest spot is Jupiter.

http://ixian.ca/pics6/jupitermoon.jpg

rantbot
08-18-2009, 07:55 PM
He wouldn't have needed a 20X telescope to see the 4 moons.
In his publications and letters with which I'm familiar, Galileo didn't devote any effort to distinguishing just what was needed to see which phenomena.

The 20x recommendation is in Sidereus Nuncius. There's a lot packed into that little book; G. discussed the discovery of multiple new stars, far more than had been known since antiquity, visible in familiar constellations - Orion, Taurus, and Cancer; the appearance of the mountains of the moon, and ways to estimate their altitudes; and of course discovery of the four largest moons of Jupiter, descriptions of their orbits, and speculation about their consequences for acceptance of the Copernican system. In later publications Galileo was concerned with the phases of Venus (which he observed in mid-1610) and with sunspots (1611). (It seems to have been a student of Galileo's who first used image projection to examine the sun; all that squinting directly at the sun may have contributed to Galileo's eventual blindness.)

So, when G. discussed the particulars of a 20x instrument (he wrote that it should magnify 400 times, but from the context it's clear that he meant area, not linear magnification), he was claiming that at least 20x was necessary to see all the phenomena he discussed in Sidereus Nuncius. The claim is probably inexact; I suspect that he settled on 20x because that was probably the power of the instrument he used when he made the discussed discoveries. There is no evidence that he worked his way up with less powerful instruments and suddenly was able to see, at 20x, these new marvels.

What G. obviously wanted to avoid was claims by those looking through the common 3x Flemish novelty instruments that Galileo's outrageous new discoveries were not visible.

20x is certainly not needed to see the Jovian moons, or the "new" stars in Orion. It was more likely essential for the lunar observations.

rantbot
08-18-2009, 08:16 PM
Also, the inner moons orbit quickly and he would only need a single night to see what is happening plus a few more to confirm his observations.
G's nightly observations of Jupiter are detailed in Sidereus Nuncius; he even noted which nights he skipped due to cloud cover. He noticed three of the moons immediately. It was several days before he noticed the fourth. The extremely narrow field of view of the "Galilean" optical system probably made it difficult for G. to realize that the remote fourth "star" was part of the system. However, it should be possible to fit all four into the field of view even when several of the moons are at their apopoints. The 1992 paper by Greco, Molesini, and Quercioli, which measured optical properties of the two telescopes and the single lens in the Florence museum (and which, lacking further data, we probably have to take as typical of telescopes of the day), gave 15 arc-min as the field of view of both the 14x and the 21x instruments.

Vincenzo Greco, Giuseppe Molesini, and Franco Quercioli, Optical Tests of Galileo's Lenses, Nature, 358.9 (July, 1992)

I have a PDF of the paper, a modest 2-pager, if anyone is interested.