A R{\o}mer time-delay determination of the gravitational-wave propagation speed

Understand

In 1676 Olaus R{\o}mer presented the first observational evidence for a finite light velocity $\cem$.

• He formed his estimate by attributing the periodically varying discrepancy between the observed and expected occultation times of the Galilean satellite Io by its planetary host Jupiter to the time it takes light to cross Earth's orbital diameter.
• Given a stable celestial clock that can be observed in gravitational waves the same principle can be used to measure the propagation speed $\cgw$ of gravitational radiation.
• Space-based "LISA"-like detectors will, and terrestrial LIGO-like detectors may, observe such clocks and thus be capable of directly measuring the propagation velocity of gravitational waves.