Measuring Speed of Light - Roemer's Method

This section describes the method used by Ole Roemer to measure the speed of light using changes of observed eclipse periods of Jupiter's moon.

Measuring the speed of light is not an easy job, since it moves very fast.

The earliest reasonably good measurement was done by the Danish astronomer Ole Rømer in 1676 using changes of observed eclipse periods of Io (one of the moons of Jupiter) as illustrated in the picture below.

Roemer's measurement is based on the following assumptions:

For example, if we record the Io eclipse interval, i1, when Earth is at location L and the Io eclipse interval, i2, when Earth is at location K, the speed of light will be the distance between L and K divided by (i2-i1).

Using this method, Roemer was able to measure the speed of light as 220,000,000 m/s. Today, we know the speed of light is 299,792,458 m/s.

Speed of Light Measurement by Ole Roemer (wikipedia)
Speed of Light Measurement by Ole Roemer

Last update: 2014.

Table of Contents

 About This Book

 Introduction of Space

 Introducion of Frame of Reference

 Introducion of Time

Introduction of Speed

 What Is Speed?

 List of Various Speeds

 Different Speeds Observed in Different Frames

Measuring Speed of Light - Roemer's Method

 Measuring Speed of Light - Fizeau's Method

 Measuring Speed of Light - Foucault's Method

 Newton's Laws of Motion

 Introduction of Special Relativity

 Time Dilation in Special Relativity

 Length Contraction in Special Relativity

 The Relativity of Simultaneity

 Introduction of Spacetime

 Minkowski Spacetime and Diagrams

 References

 PDF Printing Version