“E pur si muove.” These are the whispered words attributed to Galileo Galilei in June 1633, as he completed his recantation of the heliocentric view before the Inquisition. Today, nearly four centuries later, there’s no doubt that Earth orbits the Sun, accompanied by seven other planets and over a hundred moons, all moving at varying speeds and along distinct orbits. Besides its orbital motion, Earth rotates on its axis once a day (precisely every 23 hours, 56 minutes, and 4 seconds), tracing an elliptical, counterclockwise path from west to east. Without Earth’s rotation, days would span six months, followed by six-month nights.
Furthermore, Earth’s core, primarily composed of iron, rotates slightly faster than the mantle and crust, a phenomenon called “super rotation.” The planet’s rotational velocity varies by location, with equatorial regions experiencing the fastest speeds. By knowing Earth’s radius, we can easily calculate the equatorial speed (1666 km/h) and that of any location. For example, Madrid residents, situated at approximately 40º latitude, move at 1275 km/h. Unbeknownst to us, we travel over a thousand kilometers every hour.
Our perception of bodily movement relies on a combination of vision, hearing, muscle, joint, and skin sensors, all of which are integrated into the central nervous system to maintain balance. The vestibular system in our ears detects bodily rotations, with a detection threshold near 2º per second. This is the key to understanding the phenomenon: despite Earth’s staggering speed, its rotation rate is minimal at 0.25º per minute, falling below our vestibular system’s threshold. Just as we don’t sense speed aboard a plane or high-speed train unless there’s sudden acceleration or deceleration, we remain unaware of Earth’s constant movement.
