Rømer's determination of the speed of light
Rømer's determination of the speed of light was the demonstration in 1676 that light has a finite speed and so does not travel instantaneously. The discovery is usually attributed to Danish astronomer Ole Rømer (1644–1710), who was working at the Royal Observatory in Paris at the time.

By timing the eclipses of the Jupiter moon Io, Rømer estimated that light would take about 22 minutes to travel a distance equal to the diameter of Earth's orbit around the Sun. This would give light a velocity of about 220,000 kilometres per second, about 26% lower than the true value of 299,792 km/s.

Rømer's theory was controversial at the time he announced it, and he never convinced the director of the Paris Observatory, Giovanni Domenico Cassini, to fully accept it. However, it quickly gained support among other natural philosophers of the period, such as Christiaan Huygens and Isaac Newton. It was finally confirmed nearly two decades after Rømer's death, with the explanation in 1729 of stellar aberration by the English astronomer James Bradley.
Q2111
light has a finite speed
Concept
Q35
Danish
LOC
Q160187
Ole Rømer
PER
Q461340
Royal Observatory
LOC
Q90
Paris
LOC
Q141022
eclipse
Concept
Q319
Jupiter
CEL
Q3123
Io
CEL
Q37221
diameter
Concept
Q1348808
Earth's orbit
Concept
Q182429
kilometres per second
Concept
Q2111
299,792 km/s
Concept
Q14279
Giovanni Domenico Cassini
PER
Q269323
natural philosophers
Concept
Q39599
Christiaan Huygens
PER
Q935
Isaac Newton
PER
Q211728
stellar aberration
Concept
Q312278
James Bradley
PER
Q2898393
Rømer's determination of the speed of light
Concept
1676-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1676
DATE
1729-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1729
DATE
+1644^^http://www.w3.org/2001/XMLSchema#decimal
1644
NUMBER
+1710^^http://www.w3.org/2001/XMLSchema#decimal
1710
NUMBER
+22^^http://www.w3.org/2001/XMLSchema#decimal
22
NUMBER
+220.000^^http://www.w3.org/2001/XMLSchema#decimal
220,000
NUMBER
+26^^http://www.w3.org/2001/XMLSchema#decimal
26
NUMBER
discoverer or inventor
country of citizenship
parent astronomical body