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Section 8: Measuring the Distance to the Stars

The mathematical principles of the Copernican model resulted in pushing the sphere of the stars many thousands of times further away from the sun than it had been in the earth-centered cosmos. When the sun-centered system gained acceptance in the seventeenth century, astronomers seized the telescope to directly test the numbers. The quest for stellar parallax - a method for measuring distance to the stars-- began in earnest with Robert Hooke in 1669. He set his sites on Gamma Draconis, the bright star in the head of the constellation Draco, the Dragon, but his result was uncertain. In 1838, Friedrich Bessel solved the problem of measuring stellar distance by focusing on Cygnus 61, a small star in the constellation Cygnus, the celestial Swan. Using a precision instrument called a heliometer, he calculated it to be over 60 trillion miles away.

Aberration of light is compared to man running in rain in upper left vignette in Alexander Keith Johnston, Atlas of Astronomy, 1855.
Above, clockwise from left:
* Ole Roemer's telescope in Peder Horrebow's Basis Astronomiae; sive, Astronomiae pars Mechanica, 1735.
* Joseph von Fraunhofer's heliometer used by Bessel to find parallax in Dominique Francois Jean Arago's Popular Astronomy,1855.
* Star map of the constellation Cygnus the Swan is used to illustrate Bessel's successful determination of stellar parallax of Cygnus 61 in A Celestial Atlas by Alexander Jamieson, 1822.

Linda Hall Library of Science, Engineering & Technology
5109 Cherry Street, Kansas City, MO 64110
This exhibition is made possible by generous support from Mr. & Mrs. James B. Hebenstreit and Mrs. Lathrop M. Gates.