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Denmark 1944Scott 293 |

**Ole Rømer (1644 - 1710)**

This stamp was issued to celebrate Ole Rømer's 300th birthday.

Ole Christensen Rømer is famous for **measuring the speed of light** in 1675. He became professor at Copenhagen University, in 1677 for astronomy, in 1681 for mathematics.

Rømer proved that the speed of light is finite by exact measurements of the eclipses of the Jupiter moons (the moment when an eclipse starts - observed from earth - is delayed with growing distance from Jupiter to Earth). Rømer calculated the speed of light but missed the nowadays well-known value c = 299793 km/sec by more than 25 % (the value given by Rømer was too small). His achievement was nonetheless extraordinary if one takes into account the very limited instruments of the 17th century.

Rømer observed the moons of Jupiter at the Paris observatory. A few years after his discovery of the finite speed of light, he returned to his home country Denmark. There he worked as a professor and Astronomer Royal, and he held high political positions (for some time he was mayor of Copenhagen and chairman of the state council).

As a mathematician, Rømer worked on mathematical applications like the construction of technical instruments. The properties of the epicycloid led him to the optimized shape for gearwheels for which a smooth movement is essential. Ole Rømer introduced the Gregorian Calendar in Denmark - in 1700, February 18th was followed by March 1st.

last update 2004-12-17

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