Ole Rømer demonstrated that light travels at a finite speed in 1676, a discovery made while observing Jupiter's moon Io at the Royal Observatory in Paris. This calculation suggested light required approximately 11 minutes to traverse the distance from the Sun to Earth, marking a departure from previous assumptions regarding the instantaneous propagation of light.
Academic Foundation
Born in Aarhus in 1644, Rømer attended the Aarhus Katedralskole before matriculating at the University of Copenhagen in 1662. He studied under Rasmus Bartholin, who was then tasked with editing the astronomical observations of Tycho Brahe. During this period, Rømer gained exposure to advanced mathematics and observational astronomy. His professional trajectory initially led him to the French government, where he served as a tutor for the Dauphin and contributed to the design of the hydraulic systems at Versailles.
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While working as an assistant to Giovanni Domenico Cassini in Paris, Rømer compared eclipse timings of Jupiter's moon Io with Jean Picard. He noted that the intervals between these eclipses fluctuated based on the relative distance between Earth and Jupiter. By 1676, he concluded that these discrepancies resulted from the time light required to travel across space. This provided the basis for the first quantitative estimation of the speed of light, calculated at roughly 220,000 kilometers per second.
Public Administration and Technical Reforms
Returning to Denmark in 1681, Rømer accepted a professorship at the University of Copenhagen and married Anne Marie Bartholin. As royal mathematician, he standardized Danish weights and measures in 1683 and later facilitated the adoption of the Gregorian calendar in 1700. His civil service included tenure as Chief of the Copenhagen Police from 1705 until his death in 1710. He implemented municipal infrastructure improvements, including new street lighting with oil lamps, updated sewer systems, and enhanced fire safety equipment.
Thermometry and Legacy
While recovering from a leg injury, Rømer developed a temperature scale utilizing the boiling and freezing points of water as fixed references. His methodology influenced Daniel Gabriel Fahrenheit, who visited him in 1708 and subsequently adapted the scale into the system currently used in the United States. Despite the destruction of his personal observational records in the 1728 Copenhagen Fire, his scientific reputation was maintained through the writings of his assistant, Peder Horrebow.
Fast facts
- Born: 1644, Aarhus
- Died: 1710, Copenhagen
- Citizenship: Kingdom of Denmark
- Education: University of Copenhagen (1662)
- Occupations: Astronomer, physicist, mathematician, police officer
- Member: French Academy of Sciences, Royal Prussian Academy of Sciences
- Notable Contribution: Determination of the speed of light
Questions readers ask
How did Rømer calculate the speed of light?
He observed variations in the timing of eclipses of Jupiter's moon Io, noting that delays occurred when Earth was further from Jupiter, implying light took longer to travel the increased distance.
What was Rømer's role in the Copenhagen police force?
As Chief of Police, he reorganized the force, introduced oil-based street lamps, and managed urban regulations regarding building standards, water, and sewage.
Achievements
- Notable work: Rømer's determination of the speed of light
- Affiliated with University of Copenhagen
- Educated at University of Copenhagen and Aarhus Katedralskole
- Worked as astronomer, physicist and mathematician
