Ole Christensen Roemer was the son of a merchant, born in Aarhus, Denmark on September 25, 1644. He attended Aarhus Cathedral School in his youth and upon graduation in 1662 was sent to Copenhagen University. There he lived and studied with Erasmus Bartholin, a professor of medicine better known for his discovery of double refraction in Iceland spar. Bartholin greatly esteemed Roemer and appointed him the task of editing Tycho Brahe's manuscripts. Roemer carried on the project from 1664 to 1670 and, in 1671, journeyed to Hveen with Bartholin and Jean Picard in order to observe Brahe's observatory.
In 1676,the speed of light has been measured at least 163 times by more than 100 investigators utilizing a wide variety of different techniques, Ole Roemer made the first accurate measurement of the speed of light using Jupiter's moons.Roemer made a detailed study of the frequent eclipses of Io by Jupiter. This enabled him to accurately predict when the next eclipses will occur.However, over a period of months, Roemer's predictions were steadily off by longer and longer intervals of time. His predictions were eventually off by eight minutes.Even stranger was the fact that these predictions then became more accurate, till they were correct again. This strange cycle repeated itself again and again with great regularity.Roemer realized that this time difference was caused by the difference between the distance between the earth and Jupiter. When Jupiter was closest to earth, the eclipses happened on time. Finally in 1983, more than 300 years after the first serious measurement attempt, the speed of light was defined as being 299,792.458 kilometers per second by the Seventeenth General Congress on Weights and Measures. Thus, the meter is defined as the distance light travels through a vacuum during a time interval of 1/299,792,458 seconds. In general, however, (even in many scientific calculations) the speed of light is rounded to 300,000 kilometers (or 186,000 miles) per second.
