Galileo's Telescope
Galileo's Telescope

Astronomy, Guide to Space

Galileo’s Telescope

22 Jul , 2008 by

[/caption]Have you ever been curious about Galileo’s Telescope? Where did the idea come from and how did Galileo improve it? What did Galileo see with his telescope? What was it called and how did it work? Come along as we learn more about Galileo’s Telescope…

The History of Galileo’s Telescope

In the late summer of 1608, a new invention was all the rage in Europe – the spyglass. These low power telescopes were probably made by almost all advanced opticians and 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’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 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 about 10 times more than normal vision and but it had a very narrow field of view.

However, this limited ability didn’t stop the Galileo telescope…

What Galileo Saw With His Telescope

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 to find it “”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, but a revolution had begun.

Months passed, and Galileo’s telescope improved. On January 7, 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, all three 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! 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, and seeing Venus change from a full disk to a slender crescent. Just like any modern scientist, Galileo Galilei published his findings in 1610 in a small book titled The Starry Messenger.” No, he wasn’t the first to point a telescope towards the heavens, but Galileo was the first to do it methodically.

What Was Galileo’s Telescope and How Did It Work?

Galileo's Telescope Diagram

Galileo’s telescope was the proto-type of the modern day refractor telescope. As you can see from this diagram taken from Galileo’s own work – “The Starry Messenger” (scanned image provided courtesy of the Master and Fellows of Trinity College Cambridge) – it was a simple arrangement of lenses that first began with optician’s glass fixed to either end of a hollow cylinder. Galileo had no diagrams to work from, but used only his own system of trial and error for lens placement. In Galileo’s telescope the objective lens was convex and the eye lens was concave. Modern telescopes make use of two convex lenses. offers a wide range of refractor telescopes sold in the market today.

Galileo know that light from an object placed at a distance from a convex lens created an identical image on the opposite side of the lens. If he used a concave lens the object appeared 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 a lot of different arrangements to get the lens the proper size and distance apart, but Galileo’s telescope remained the most powerful and accurately built for a great many years.

Where Is Galileo’s Telescope Today?

Galileo's Telescope Replica

Galileo's Telescope Replica

400 years later, Galileo’s Telescope still survives in the constant care of the Istituto e Museo di Storia della Scienza 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!

CSIRO Australia

Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status. (Tammy passed away in early 2015... she will be missed)

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