Maker's Name: 
Norman Heckenberg
Where made: 
100 × 5.5 × 5.5 cm

This telescope was built in 2009 by Professor Norman Heckenberg to celebrate the 400th anniversary of Galileo's use of the telescope to observe the surface of the Moon and discover satellites orbiting Jupiter. It is based on surviving telescopes made by Galileo in the Museo Galileo in Florence, and information gathered by Jim and Rhoda Morris, who have built exact replicas for many museums, including the Powerhouse Museum in Sydney. Although the tube is cardboard rather than the original wood, the lenses have focal lengths of 1000mm and -50mm, in the ranges that Galileo used (he is said to have made at least 80 telescopes). The lenses are uncoated and not achromatic, just like the ones he ground. The objective is also apertured down to use only the central part, as Galileo did.

This type of telescope produces an erect image with only two lenses, but has a very small field of view (it is like looking down a very long pipe and, with a magnification of X20, you cannot see all of the Moon at once), although you can scan the view somewhat by moving your eye without moving the telescope. Although the field of view is small, the image quality compares favourably with cheap modern binoculars.

The focal length of a lens is its most important characteristic. It is a measure of how strongly it converges or diverges light. The shorter the focal length, the greater the optical power because it bends the light rays more strongly and focuses them in a shorter distance. As discussed on the Searchlight Mirror page, the effect of lenses on light is described by ray tracing, which was developed as part of the ballistic model of light. Ray tracing is a geometical construction of the way light passses through an optical system, based on it moving in straight lines between lenses and mirrors and being deflected according to simple laws at these elements. When rays that have spread apart from an object meet again we know that an image will be formed and its size and position can be found.

Not only was Galileo a keen astronomer, he also conducted the first experiment investigating the speed of light. In 1638 he and an assistant, each with a lamp that could be covered and uncovered, stood various distances apart, facing each other. When the assistant saw Galileo uncovering his lamp he would uncover his as well. By measuring the time between uncovering his lamp and seeing his assistant uncover the other Galileo hoped that he would be able to measure the speed of light. He came to the conclusion that "If not instantaneous, it is extraordinarily rapid", at least 10 times the speed of sound.

This item is part of the UQ Physics Museum ‘2015, International Year of Light’ Tour
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  • objective 
  • eyepiece