This paper describes an experiment regularly presented to advanced undergraduate Physics students at the Universidad de los Andes in Bogotá, Colombia. The purpose of the experiment is to use high-resolution solar spectra to measure the horizontal speed of the laboratory caused by terrestrial rotation. Using this result, the radius of the Earth can be deduced. It is also possible to observe the Earth’s motion towards or away from the Sun, and hence compute our planet’s orbital eccentricity.