Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Measuring the speed of light
Name: Virginia
Status: Other
Age: N/A
Location: N/A
Country: N/A
Date: N/A 

How do you measure the speed of light?

Since light moves very fast, you either need to measure its motion over a very long distance, or else you need to be very fast about it. The first measurements (including one based on the orbits of the moons of Jupiter) used the long-distance approach, but with modern very fast clocks and other technology it is not that hard to measure the few nanoseconds it takes for light to travel a certain distance. Actually, nobody ever has to measure the speed of light again because it is been established as a constant that is used to define the metric unit of length (the meter) in terms of the unit of time (the second) which we can measure much more precisely.

A Smith

Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory