Galileo's Refracting Telescope

Topics: Lens, Telescope, Refracting telescope Pages: 10 (2494 words) Published: March 5, 2009

Experimental History
Research Topic: Galileo’s Refracting Telescope

Patrick Doan
Kevin Le
Kevin Tumang

11 PHYS 71
Principle Aim: To construct a recreation of the Galilean refracting telescope and a Newtonian reflecting telescope

Aim: To build on the ideas brought by foreigners to Venice of a primitive reflecting telescope developed by Dutch spectacle makers in Middelburg. That is, to study the properties of a concave and a convex lens in terms of magnification. We aim to collaborate these ideas into recreating a similar refracting telescope to the one reinvented by Galileo in the months of 1608. We will also try to make a more powerful and superior apparatus than Galileo's original three-powered telescope.


The history of the telescope goes back to the Greek philosopher Aristotle. Though commonly believed that scientists had invented the telescope rather it was invented by craftsmen. Due to that theory the origin of the telescope is in much inaccessibility and therefore impossible for us to study since the craftsmen were often not accounted for historically and by large illiterate and therefore lost. There were Dutch glass makers before Galileo who made a telescope consisting of one concave and one convex lens with a magnification of tree or four times. They tried to sell them to get a patent. The invention of this telescope quickly spread and before long Galileo heard of the telescope and immediately set to work. For the record it was Galileo who made the telescope famous due to the fact that the Dutch glass makers wanted to sell the device because to get a patent and that Galileo wanted observe the sky and planets. The scientific theory of during this period was that it was a device for “seeing faraway things seem close by”.

Galileo Galilei (1564-1642)

Galileo Galilei was born near Pisa, in Tuscany, on February 15, 1564. He was an Italian physicist and astronomer, who pioneered the scientific revolution that flowered from the works of the well known English physicist known as Isaac Newton. Galileo learned from the monks at Vallombrosa and continued on his education by entering the University of Pisa in 1580 or 1581 to study medicine. Although the outline of his studies was uncongenial to him, it did give him a useful introduction to current versions of Aristotelian physics. Galileo came to see both the presently dominant physics of the Greek philosopher Aristotle and the Roman Catholic theology influenced by it as restricting physical inquiry. Galileo’s main contributions to astronomy were the use of the telescope in observation, and the finding of lunar mountains and valleys, the four biggest satellites of Jupiter, the different phases of Venus, and sunspots. In Physics, he discovered the laws governing falling bodies and projectiles which is a great use even up to now.

The scientific theory behind our experiment of the refracting telescope is that it uses lenses bend light making things seem larger. Light comes through to the objective lens and then gets refracted to the eyepiece lens and then it gets into our eyes for an image. As the convex objective lens moves further away from the concave eyepiece the image that is being refracted gets bigger but blurrier. Diagram 1 below illustrates the process of a refracting telescope:

Diagram 1


• 2 cardboard tubes (50 and 60 mm in diameter)
• Convex lenses (biconvex 100cm FL, biconvex 25cm FL, biconvex 5cm FL, convex unmarked telescope lens, biconcave 20 cm FL, biconcave 20cm FL [2]) • Tape measure (construction and fashion)
• Tri-square
• Masking tape
• Black spray-paint
• Felt fabric
• PVA glue
• Saw
• Sandpaper
• 2B pencil
• Blu-tack
• Tripod


Part One: Testing the lens focal lengths (the sun test):

1. The apparatus was set up as shown in photo 1. (With the purpose to allow the lens to move in a linear path as...

Bibliography: Microsoft Encarta Encyclopedia Standard, 2005, CD ROM, Microsoft Corporation, U.S.A
Encyclopedia Britannica (Micropaedia, Book 5), 1987, Encyclopedia Britannica, Inc, Chicago
Encyclopedia Britannica (Macropaedia, Book 19), 1987, Encyclopedia Britannica, Inc, Chicago
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