Cool Romer Io Jupiter Speed Of Light Ideas. He did this using timings obtained by giovanni cassini of the eclipses of jupiter’s moons. The earliest reasonably good measurement was done by the danish astronomer ole rømer in 1676 using changes of observed eclipse periods of io (one of the moons of jupiter) as illustrated in the picture below.
He did this 166 years before christian doppler described what we now call the doppler effect and the mechanism in 1842. The revolution time can be measured by calculating the time interval between the moments io enters or leaves jupiter's shadow. C = 2.14 x 10 8 meters per second this is 70% of today’s value:
