The Palermo circle

The Palermo circle

Fig. 1.15 . This instrument, built by Jesse Ramsden (1735-1800) of London, was used by Giuseppe Piazzi (1746-1826) to obtain precise measurements of stellar positions, with an accuracy of a few seconds of arc after observing each star for at least two nights. In the process, Piazzi unexpectedly discovered the first asteroid, 1 Ceres, in 1801. The telescope has a 7.5-cm objective lens. The altitude scale (5 feet in diameter) was read with the aid of two diametrically opposed micrometer microscopes; the azimuth scale (3 feet in diameter) was also read by means of a micrometer microscope.

Copyright 2010, Professor Kenneth R. Lang, Tufts University