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© Copyright 2003, Jim Loy
This is a model of a sextant, a navigational instrument for measuring angles between the horizon and some object in the sky, like the sun or a star. Light from the horizon (the horizontal yellow line) goes through a flat piece of glass and into the eyepiece, which is a small telescope. Light from the sun or a star is reflected off a small mirror on top of the instrument, onto a second mirror (along side the flat piece of glass mentioned above), and into the eyepiece. The navigator then sees two images, the horizon and the sun (or star) side by side. He/she can then measure the angle between them on a scale at the bottom of the instrument. The scale goes from 0 to 120 degrees. Move the large red dot, to measure different angles. An earlier instrument, called a quadrant or octant, was the same instrument, but it could only measure angles from 0 to 90 degrees.
The above Java interactive demonstration was created with Cinderella (a geometry program).
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