Measuring the Size of the Earth
Using traceroute
Traceroute is an internet
program to find transmission times between nodes on an IP route.
-
Conceptual Simplicity:
Time is longer
for longer hauls, in proportion to the distance.
-
Flexibility:
Many targets
available
-
Ease of Execution:
Data collection
takes a minute. No equipment.
-
Quality of Results:
10% result. Systematically too big (hills!)
-
Easy Data Analysis:
Just ratio-and-proportion
OR basic trig
You need:
Computer connected to the
Internet
Proceedure:
-
Find an internet address some distance
away, either on an island OR at the perephery of a continent
(IDEA: You are looking to send IP packets across sea-buried fiber optic
cables, not land lines!)
-
Run traceroute <ip#> and
study output for the average time jump across the fiber optic cable.
-
Divide the time by 2 (traceroute
records
roundtrip times)
-
Multiply the time by 1.98 x 108m/s,
the
speed of light in the cables (see http://comp.dcom.lans.ethernet_FAQ,
for example reference to measured speed in optical fiber cable). This gives
a measuement of the distance between the endstations on the sea route.
-
Use a string (or calipers) and a globe to compare the
distance (along a great circle) between the endstations for the sea
route and circumfrence of the globe.
-
Use ratio and proportion to determine the circumfrence of
the earth and thus the radius
Example Traceroute Data Sets
Example Analyses
Note: traceroute is called tracert on windows
machines.