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The Discoveries of Galileo – Part 1: Jupiter


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The Discoveries of Galileo – Part 1: Jupiter

Ed LaBelle, Psalm 19 Astronomy

We amateur astronomers should all be familiar with who Galileo di Vincenzo Bonaulti de Galilei aka Galileo Galilei (1564-1642) was. He has been called the father of observational astronomy. I happened upon a book the Austin Public Library, Discoveries and Opinions of Galileo, first published in 1957 by Stillman Drake and I was fascinated by the writings of Galileo. Drake was a Canadian historian of science best known for his complete works on Galileo. In this book Drake has translated many of Galileo’s letters and other publications. In the 1600’s the language of the educated class was Latin. Galileo was a revolutionary in that he wrote about his philosophical i.e. scientific observations in Latin and in the local Italian dialect. He wanted the masses to read his writings, not just the elite educated class!

The painting in figure 1 by Giuseppe Bertini shows Galileo courting the reigning Medicini family of Florence for financial support. He was employed as the tutor of mathematics to one son, Cosimo II, in the summer of 1605. Five years later the young Cosimo would become the Grand Duke of Tuscany. It is believed that the Duke, after looking through the telescope, rewarded Galileo by appointing him as the chief mathematician and philosopher of Tuscany.

Galileo first heard of an invention out of Holland in the year 1608 called a “spyglass” that magnified distant objects. The invention of the spyglass is attributed to Hans Lipperhey who was a spectacle maker. He developed one of the first refracting telescopes "for seeing things far away as if they were nearby." Lipperhy’s spyglass could magnify distant objects to about 3-4x.

Galileo wrote, “About ten months ago a report reached my ears that a certain Fleming had constructed a spyglass by means of which visible objects, though very distant from the eye of the observer, were distinctly seen as if nearby.” So, Galileo used his talents to make his own spyglass in the summer of 1609.

Figure 2 shows a replica of one of his first spyglasses. It’s about 39” long (980mm) with a tube diameter of about 1.5” (37mm) and it gave him a magnification of ~ 20x.

 

Galileo pointed his spyglass to the night sky and was one of the first humans to see the beauty and majesty of God’s creation up close. Galileo made both simple and detailed drawings of his celestial observations depending on how the resolution he could see in his spyglass.

I want the focus on this article to be Galileo’s observation of that wandering star known to everyone in the 17th century and today as Jupiter. And I want to compare Galileo’s nightly drawings of that celestial object to today’s advanced night sky astronomy software.

On a clear, cold night in January 1610 Galileo turned his spyglass toward a bright wandering star. Until this point in human history people didn’t know that the five visible “wandering stars” were planets and not stars. This image from the Let There Be Night website (figure 3) gives an approximate idea of the magnification and a narrow field of view of what Jupiter may have looked like to Galileo. But even with that narrow view Galileo was able to note some “stars” next to Jupiter. Galileo of course was astonished! He wrote,

“But what exceeds all wonders, I have discovered four new planets and observed their proper and particular motions, different among themselves and from the motions of all the other stars; and these new planets move about another very large star [Jupiter] like Venus and Mercury, and perchance the other known planets, move about the Sun.”

 

 

Imagine you were in Galileo’s shoes four hundred and ten years ago and you would probably think the tiny points of light around the bright planet were stars too! Galileo noticed that the smaller companion stars changed position from night to night. He made detailed sketches of Jupiter and its “stars” from January 7 to January 15, 1609 (figure 4, left panel). I used Stellarium astronomy software to validate the position of Jupiter’s moons on the same dates as his observations (figure 4, right panel).

Note his first drawing on January 7, 1610 in figure 4. See the position of the “stars” he drew and compare them to the Stellarium software. I have put a ”J” over the planet Jupiter in both images. I am amazed at how well the algorithms from the Stellarium software can reach back into time and match up with the first drawings of Jupiter magnified through a telescope!

Galileo drew the position of the “stars” on seven nights to track their movement. You can see the movement of the companion stars in the software and compare them to his drawings. Note that because of the limited magnification of the optics of Galileo’s primitive lenses that he sometimes could not resolve an individual “star” if it was too close to another star or Jupiter i.e. his January 10 drawing.  I was stunned at how accurate our modern software is in going back in time to display the position of celestial objects.

On a personal note, I purchased my first telescope, a Meade DS-2130 5” GoTo reflector, in 2009. I remember being out at a dark location one summer night in Lago Vista, Texas in 2012 and looking at Jupiter. I could only see three of the Galilean moons much like the January 8 Stellarium image. I kept asking myself over and over, “Where is the fourth moon?” Then about 30 minutes later I noticed a small white pimple on the right side of Jupiter. As I watched in awe, I could see in real time as the pimple grew and then completely separated from Jupiter as the fourth moon. And I remember thinking to myself, “This must have been the same awe Galileo felt when he first observed this same thing for the first time!”

Back to Galileo in 1610, it wasn’t long before Galileo realized these were not stars but what he called planets revolving around the “star” named Jupiter. It was a stunning revelation to Galileo: small planets are moving around a “star” just like Venus and Mercury revolves around our Sun!

 

This was definitely a “Eureka!” moment for Galileo! He honored the Medicini family and Cosimo II, who became Grand Duke of Tuscany in 1609, by naming these four “planets” the Medicea Sidera (Medicean stars) in his 1610 pamphlet Sidereus Nuncius, “Starry Messenger” (figure 5).

 

 

 

In the next installments of this series I will cover Galileo’s observations of sunspots, the Moon, Venus, and the Milky Way. A little preview: his writings on sunspots in 1613 are what initially got him in trouble with the Roman Catholic Church!

Ed LaBelle has been a member of Austin Astronomical Society since 2010. He has worked as an engineer in the semiconductor industry for 30 years. Ed is the founder of the Psalm 19 Astronomy Society, a sidewalk astronomy ministry, based in Austin, Texas USA.


  • Special Ed, Scott in NC, Mak2007 and 32 others like this


21 Comments

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bruceosterberg
Jan 01 2021 08:16 AM

Great Article, who Knew

    • E-Ray and fernisaurus like this
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SiriusLooker
Jan 01 2021 11:42 AM

Nice article, -- Interesting that he(Galileo) was more interested in Military aspects of the (also called --the Looker) because he was able to profit from it at first, as did Hans, who also sold his (Lookers-Scopes) to Dutch army during the times.

 Sadly Galileo appear not to *(Wander-pun intended) around Jupiter when he did his drawings of the Moons of Jupiter. Because on Jan 8th barely just over 2degs away was the other planet of Uranus from Jupiter.

 

Dennis

    • kolsen and E-Ray like this
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fallenstarseven
Jan 01 2021 04:44 PM

Interesting article, and some illustrations I hadn't seen before.  Noted that your second paragraph references Galileo's relationship with the Medicis in Florence, but the Bertini illustration shows him demonstrating the scope to the Doge and Venetian lawmakers in Venice in 1609, who are not part of the Tuscan state.  May want to correct the illustration to match the paragraph reference to the Medici.

    • E-Ray likes this

Thanks fallenstarseven for catching the issue with the figure 1 "courting the reigning Medici family." I will correct that statement for future use.

Regards, Ed

Interesting article, and some illustrations I hadn't seen before.  Noted that your second paragraph references Galileo's relationship with the Medicis in Florence, but the Bertini illustration shows him demonstrating the scope to the Doge and Venetian lawmakers in Venice in 1609, who are not part of the Tuscan state.  May want to correct the illustration to match the paragraph reference to the Medici.

    • fallenstarseven likes this

Thanks Dennis. Yes, Galileo initially was making the spyglass available for military use.

 

Ed

Nice article, -- Interesting that he(Galileo) was more interested in Military aspects of the (also called --the Looker) because he was able to profit from it at first, as did Hans, who also sold his (Lookers-Scopes) to Dutch army during the times.

 Sadly Galileo appear not to *(Wander-pun intended) around Jupiter when he did his drawings of the Moons of Jupiter. Because on Jan 8th barely just over 2degs away was the other planet of Uranus from Jupiter.

 

Dennis

    • Cali likes this

Nice article.

 

Someone actually built one.

 

Video "Looking through Galileo's Telescope"

 

- Cal

    • Ford Prefect, E-Ray and RainMaggedon like this

I remember reading a few interesting paragraphs about Galileo's observations in a history of western science text many years ago. This was a nice read going much deeper on the subject. I look forward to future parts. Thanks.

 

Art

    • E-Ray likes this
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iseegeorgesstar
Jan 10 2021 11:18 AM

Excited for the second article -- thanks!

Hi Cal,

That's an interesting link and I had watched that video last summer. Here's a link to Jim and xxxxxx Morris's effort to create exact replicas of Galileo's scopes including the gold leaf decorations. They spent a lifetime making replica of other scientific instruments including the Curie's apparatus for discovering radium, Mosely spectrascope, etc. This website is around 10 years old but still has a lot of interesting information and detail on how Jim and Rhoda made their replicas.

 

Regards, Ed

 

http://www.scitechan...ileo_telescope/

 

Nice article.

 

Someone actually built one.

 

Video "Looking through Galileo's Telescope"

 

- Cal

    • Cali likes this
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Ford Prefect
Jan 12 2021 12:58 PM

Nice article.

 

Someone actually built one.

 

Video "Looking through Galileo's Telescope"

 

- Cal

Hi,

a member of my astronomy club in Rome made a replica (even using same materials) years ago, and we used it at a public event to illustrate the actual view through it. We even tried to use it with a very simple alt-az mount (since Galileo never described how he mounted the telescope. The drawings of mounted telescopes are years after the Sidereus Nuncius). It is amazing how small is the field of view and how hard is to point the telescope.

 

Some astronomers in Arcetri Astronomical Observatory in 2009-2010 tried even to grind and to polish the lenses using the same method used at the time, to reproduce also the aberrations due to the not so perfect figure of the lenses and homogeneity of the glass. If you look at his drawings, you see spikes on stellar objects and sort of "halo" that Galileo drew like a thicker outline around bright planets.

I'm looking forward to Part II.

 

And here I complain about my 'lil 127mm Mak.

 

- Cal

E-Ray,

 

Very interesting article--nicely done!  As you know, I share your respect for Galileo and his accomplishments.  The video that was linked upthread was also quite informative.

 

I noticed you mentioned Stillman Drake's translation of Sidereus Nuncius.  Have you seen the translation by Albert Van Helden?  It is a later translation than Drake's and contains many explanatory notes.  You might want to take a look if you aren't familiar with it.

 

Sidereus Nuncius translated by Albert Van Helden, University of Chicago Press, 1989

 

Regards.

    • E-Ray likes this

E-Ray,

 

Very interesting article--nicely done!  As you know, I share your respect for Galileo and his accomplishments.  The video that was linked upthread was also quite informative.

 

I noticed you mentioned Stillman Drake's translation of Sidereus Nuncius.  Have you seen the translation by Albert Van Helden?  It is a later translation than Drake's and contains many explanatory notes.  You might want to take a look if you aren't familiar with it.

 

Sidereus Nuncius translated by Albert Van Helden, University of Chicago Press, 1989

 

Regards.

Hey Voyager I, thanks for the heads up about Albert Van Helden. I'll have to request his book from my library!

 

Regards, Ed

I got this version at a library of congress tent sale years ago.  It was "only" 70 bucks as I recall.  I would not have paid 250. I donated it to the Astronomy Lyceum in Magdalena New Mexico in 2018. It included interesting articles in addition to the facsimile and translation.

 

https://www.amazon.c...i/dp/1929154496

    • GeoNole94 likes this

Thanks for doing this series, a true pioneer.

For the 2009 International Year of Astronomy, some folks created a telescope kit that allows the builder to create a refractor can mimic the optical performance of Galileo's telescope (but which provides more modern 50 mm views as well).  Called the "Galileoscope", It costs about $70 and is still available for purchase here: https://explorescien...ts/galileoscope

 

The educational target is school age kids, but nothing says adults can't have fun building it if they have never done such a thing.

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rodney j johnson jr
Mar 11 2021 12:02 AM

thanks for writing this in a style i can understand!

Great article.

I also remember observing Jupiter, seeing three moons, wondering where the fourth was and then it appeared.  I knew the moons orbited Jupiter and eclipses are analyzed, timed and predicted but to see it happen with my own eyes changed how, from my own backyard, I observe and think about the universe.

Appreciate including your personal note.

Great lucid article!

Galileo became even more convinced he was observing moons when he recognized their alignment with the ecliptic.

Lippershey likely had a better than average small scope but he was denied a patent due to prior art.

I recall reading he was a bit upset that he learned of the spyglass only days before Hans was to demonstrate to sell it to leaders in Venice, IIRC. I only vaguely recall that Hans spyglass inverted the image, but Galileo’s convex-concave combo did not invert the view.

I’m curious if Galileo had superior quality glass coming from Florence?

Surprised I didn't see this topic when it was first posted - but a great read through!

Only thing I'll add, if you haven't read the Sidereus Nuncius you're seriously missing out. It's amazing, as are Galileo's sketches marking the orbit of Jupiter's moons. It's outstanding. And you can read it online, for free, or download it to your reading tablet here: https://www.gutenberg.org/ebooks/46036

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Dave Mitsky
Jul 23 2021 11:14 PM

Thanks for posting this interesting article!

 

Years ago at a star party I looked through a replica of Galileo's refractor that someone had built.  The field of view was tiny.



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