Earth rotation via doppler shifts?

Abstract

Stedman cites many successfully experiments regarding the measurement of the Earth’s rotation via the Sagnac effect. He addresses the important fact that Sagnac measurements can be interpreted as a Doppler effect. In a rotating interferometer all optical components are moving, and therefore each one produces a Doppler shift. Accounting for the total contribution of all the mirrors, the standard Sagnac formula is recovered. We want to clarify the fact that we referred to the value of the Earth’s rotational rate as an example of what we call low rotational speed rather than a proposal to measure the Earth’s rotation by means of our apparatus. As suggested by a reviewer, one could mount the mirror on a motorized rotation stage and move it very slowly. Our apparatus may be used to show students how to detect very low rotational speeds.