He found that the times of these eclipses varied with the distance between Jupiter and the Earth. He deduced that light must take extra time to travel from Jupiter to Earth when the planet was further. From his knowledge of the difference in distance and the changes in the eclipse times he worked out the speed of light. The velocity of light is one of the most important universal constants there is. For all waves, there is a relationship between the velocity, wavelength and a quantity called frequency.
Frequency is how many waves pass a given point per second.
The relationship is given by the simple equation below. The unit per second is called a Hertz . He built his own telescopes which were better than any that existed at the time. In 1800 he performed a famous experiment where he tried to measure the temperature of different colours of the spectrum by placing a thermometer on each colour. He found to his amazement that the hottest part of the spectrum was in a place where there was no colour at all .