The original Galileo telescope, which is preserved today at the Museo Galileo in Italy. Credit: museogalileo.it

What is Galileo’s Telescope?

Article Updated: 13 Jul , 2016

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In 1610, Italian astronomer Galileo Galilei looked up at the heavens using a telescope of his making. And what he saw would forever revolutionize the field of astronomy, our understanding of the Universe, and our place in it. Centuries later, Galileo’s is still held in such high esteem; not only for the groundbreaking research he conducted, but because of his immense ingenuity in developing his own research tools.

And at the center of it all is Galileo’s famous telescope, which still inspires curiosity centuries later. How exactly did he invent it. How exactly was it an improvement on then-current designs? What exactly did he see with it when he looked up at the night sky? And what has become of it today? Luckily, all of these are questions we are able to answer.

Description:

Galileo’s telescope was the prototype of the modern day refractor telescope. As you can see from this diagram below, which is taken from Galileo’s own work – Sidereus Nuncius (“The Starry Messenger”) – it was a simple arrangement of lenses that first began with optician’s glass fixed to either end of a hollow cylinder.

Diagram of Galileo's telescope, taken from Sidereus Nuncius. Credit: hps.cam.ac.uk

Diagram of Galileo’s refractor telescope, taken from Sidereus Nuncius (1610). Credit: hps.cam.ac.uk

Galileo had no diagrams to work from, and instead relied on his own system of trial and error to achieve the proper placement of the lenses. In Galileo’s telescope the objective lens was convex and the eye lens was concave (today’s telescopes make use of two convex lenses). Galileo knew that light from an object placed at a distance from a convex lens created an identical image on the opposite side of the lens.

He also knew that if he used a concave lens, the object would appear on the same side of the lens where the object was located. If moved at a distance, it appeared larger than the object. It took a lot of work and different arrangements to get the lens the proper sizes and distances apart, but Galileo’s telescope remained the most powerful and accurately built for a great many years.

History of Galileo’s Telescope:

Naturally, Galileo’s telescope had some historical antecedents. In the late summer of 1608, a new invention was all the rage in Europe – the spyglass. These low power telescopes were likely made by almost all advanced opticians, but the very first was credited to Hans Lippershey of Holland. These primitive telescopes only magnified the view a few times over.

Much like our modern times, the manufacturers were quickly trying to corner the market with their invention. But Galileo Galilei’s friends convinced his own government to wait – sure that he could improve the design. When Galileo heard of this new optical instrument he set about engineering and making improved versions, with higher magnification.

Galileo Galilei showing the Doge of Venice how to use the telescope by Giuseppe Bertini (1858). Credit: gabrielevanin.it

Galileo Galilei showing the Doge of Venice how to use the telescope by Giuseppe Bertini (1858). Credit: gabrielevanin.it

Galileo’s telescope was similar to how a pair of opera glasses work – a simple arrangement of glass lenses to magnify objects. His first versions only improved the view to the eighth power, but Galileo’s telescope steadily improved. Within a few years, he began grinding his own lenses and changing his arrays. Galileo’s telescope was now capable of magnifying normal vision by a factor of 10, but it had a very narrow field of view.

However, this limited ability didn’t stop Galileo from using his telescope to make some amazing observations of the heavens. And what he saw, and recorded for posterity, was nothing short of game-changing.

What Galileo Observed:

One fine Fall evening, Galileo pointed his telescope towards the one thing that people thought was perfectly smooth and as polished as a gemstone – the Moon. Imagine his surprise when found that it, in his own words, was “uneven, rough, full of cavities and prominences.” Galileo’s telescope had its flaws, such as a narrow field of view that could only show about one quarter of the lunar disk without repositioning.

Nevertheless, a revolution in astronomy had begun! Months passed, and Galileo’s telescope improved. On January 7th, 1610, he turned his new 30 power telescope towards Jupiter, and found three small, bright “stars” near the planet. One was off to the west, the other two were to the east, and all three were in a straight line. The following evening, Galileo once again took a look at Jupiter, and found that all three of the “stars” were now west of the planet – still in a straight line!

Cardinal Bellarmine had written in 1615 that the Copernican system could not be defended without "a true physical demonstration that the sun does not circle the earth but the earth circles the sun". Galileo considered his theory of the tides to provide the required physical proof of the motion of the earth. This theory was so important to him that he originally intended to entitle his Dialogue on the Two Chief World Systems the Dialogue on the Ebb and Flow of the Sea. For Galileo, the tides were caused by the sloshing back and forth of water in the seas as a point on the Earth's surface sped up and slowed down because of the Earth's rotation on its axis and revolution around the Sun. He circulated his first account of the tides in 1616, addressed to Cardinal Orsini. His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure. If this theory were correct, there would be only one high tide per day. Galileo and his contemporaries were aware of this inadequacy because there are two daily high tides at Venice instead of one, about twelve hours apart. Galileo dismissed this anomaly as the result of several secondary causes including the shape of the sea, its depth, and other factors. Against the assertion that Galileo was deceptive in making these arguments, Albert Einstein expressed the opinion that Galileo developed his "fascinating arguments" and accepted them uncritically out of a desire for physical proof of the motion of the Earth. Galileo dismissed the idea, held by his contemporary Johannes Kepler, that the moon caused the tides. He also refused to accept Kepler's elliptical orbits of the planets, considering the circle the "perfect" shape for planetary orbits.Cardinal Bellarmine had written in 1615 that the Copernican system could not be defended without "a true physical demonstration that the sun does not circle the earth but the earth circles the sun". Galileo considered his theory of the tides to provide the required physical proof of the motion of the earth. This theory was so important to him that he originally intended to entitle his Dialogue on the Two Chief World Systems the Dialogue on the Ebb and Flow of the Sea. For Galileo, the tides were caused by the sloshing back and forth of water in the seas as a point on the Earth's surface sped up and slowed down because of the Earth's rotation on its axis and revolution around the Sun. He circulated his first account of the tides in 1616, addressed to Cardinal Orsini. His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure. If this theory were correct, there would be only one high tide per day. Galileo and his contemporaries were aware of this inadequacy because there are two daily high tides at Venice instead of one, about twelve hours apart. Galileo dismissed this anomaly as the result of several secondary causes including the shape of the sea, its depth, and other factors. Against the assertion that Galileo was deceptive in making these arguments, Albert Einstein expressed the opinion that Galileo developed his "fascinating arguments" and accepted them uncritically out of a desire for physical proof of the motion of the Earth. Galileo dismissed the idea, held by his contemporary Johannes Kepler, that the moon caused the tides. He also refused to accept Kepler's elliptical orbits of the planets, considering the circle the "perfect" shape for planetary orbits.

Galileo’s Sidereus Nuncius (“Starry Messenger”) shared the discoveries he made of Jupiter with his telescope. Credit and Copyright: brunelleschi.imss.fi.it

And there were more discoveries awaiting Galileo’s telescope: the appearance of bumps next to the planet Saturn (the edges of Saturn’s rings), spots on the Sun’s surface (aka. Sunspots), and seeing Venus change from a full disk to a slender crescent. Galileo Galilei published all of these findings in a small book titled Sidereus Nuncius (“The Starry Messenger”) in 1610.

While Galileo was not the first astronomer to point a telescope towards the heavens, he was the first to do so scientifically and methodically. Not only that, but the comprehensive notes he took on his observations, and the publication of his discoveries, would have a revolutionary impact on astronomy and many other fields of science.

Galileo’s Telescope Today:

Today, over 400 years later, Galileo’s Telescope still survives under the constant care of the Istituto e Museo di Storia della Scienza (renamed the Museo Galileo in 2010) in Italy. The Museum holds exhibitions on Galileo’s telescope and the observations he made with it. The displays consist of these rare and precious instruments – including the objective lens created by the master and the only two existing telescopes built by Galileo himself.

Thanks to Galileo’s careful record keeping, craftsmen around the world have recreated Galileo’s telescope for museums and replicas are now sold for amateurs and collectors as well. Despite the fact that astronomers now have telescopes of immense power at their disposal, many still prefer to go the DIY route, just like Galileo!

A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory. Credit: Wikipedia Commons/Mike Dunn

A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory. Credit: Wikipedia Commons/Mike Dunn

Few scientists and astronomers have had the same impact Galileo had. Even fewer are regarded as pioneers in the sciences, or revolutionary thinkers who forever changed humanity’s perception of the heavens and their place within it. Little wonder then why his most prized instrument is kept so well preserved, and is still the subject of study over four centuries later.

We have written many interesting articles on Galileo here at Universe Today. Here’s

Astronomy Cast also has an interesting episode on telescope making – Episode 327: Telescope Making, Part I

For more information, be sure to check out the Museo Galileo‘s website.

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2 Responses

  1. Aqua4U says:

    Just try to imagine what if felt like to be the first one to see the moons of Jupiter or the rings of Saturn! Talk about mind blowing!

    Even today we have ‘Old school’ scientists who refuse to accept change. Rather like the clergy in Gallileo’s time? Such is the nature of collectivized thought. One needs reproducible evidence and bonified credentials to even be heard.

    Bottom line is… Seek a higher level education if you have a desire to change science. That is IF you can afford it! This ‘filtering’ down effect is crucial for the integrity of our sciences, but on wonders what has been sidelined or ignored due to the process…

    • Aqua4U says:

      There are of course exceptions to this rule, but generally speaking.. something that shifts the scientific paradigm has to be undeniably and unequivocally apparent to the community. But you knew that….

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