NAWCC Bulletin
October 1997 Volume 39/5 Number 310
Table of Contents

About the Cover

On the front cover, E.W. Willard's clock with Jovilabe which won first prize in the Complicated Clocks category in the Craft Contest in Atlanta in June 1997. A Jovilabe shows the motions of the four Jupiter satellites discovered by Galileo in 1610. in order of distance from Jupiter they are: 1) Io, 261.9-thousand miles from Jupiter with orbital period of 1.77 days; 2) Europa, 416.8-tyousand miles, 3.55 days; 3) Ganymede, 664.8-thousand miles, 7.15 days, and 4) Callisto, 1,170.0-thousand miles, 16.69 days. The satellites on this Jovilabe orbit Jupiter in the times listed above. The curved line across the bottom of the dial represents the horizon and separates night and day. The sun (revolving once in 24 hours), also moves slowly outwards in a slot in the arm of the sun ring (indicating its height in the sky) until the summer solstice and then inwards so that it is low in the sky at the winter solstice.
     The moon than makes one revolution in 24 hours and 50.5 minutes, moves counterclockwise with respect to the 29.5 divisions on the one ring and indicates the age of the new moon. Four additional dials show minutes, the date, month and day of the week. The mechanism is powered by a one-rpm synchronous motor and can be operated manually by a hand crank for setting and demonstration purposes. One turn of the crank equals 24 hours of time. the clock and Jovilabe contain 48 wheels and pinions with over 2400 teeth and required about 1000 hours to design and construct.