Sagnac Effect Animation

Please click the link below for a full discussion of this animation. 
The Sagnac effect is a change in light wave propagation times of light confined to a closed path where the path is rotating.  The changes are linear in the rate of rotation of the path.  As such, these changes are used as signals for very accurate rotation rate sensors or gyros.
In this animation photons propagate around the rim of a counter-clockwise (CCW) rotating disk of radius R.  The tangential speed of points on the rim of the disk is β times the speed of light, c.  The photons require a time 
tLight=2 n π R/c

to circumnavigate the rim an integer n times. Meanwhile the disk rim has moved a tangential distance 
D=β*c*tLight where β=v/c and v is the tangential speed of the rim.
This results in the times of intersection of CW and CCW photons with the  launch plane of the photons on the disk rim:
tCW=tLight/(1+β)
tCCW=tLight/(1-β)
The animation reports the times of intersection as well as the time difference between intersections.

Sagnac Equations

Rotation Speed Rotation beta