Coriolis Effect Described Centuries Before Coriolis Lived

Giovanni Battista Riccioli is a name that perhaps still holds some resonance with astronomy history buffs. Otherwise, the 17th Century Jesuit priest is relatively unknown. Still, he should be the one getting credit for discovering the Coriolis effect.

The concept refers to the motion of objects in a rotating system, and is now taken into account by meteorologists when analyzing atmospheric front formation, and by artillery gunners when they plot new trajectories into their guns.

What the effect describes is the apparent deflection of moving objects when they are observed from a rotating reference frame. The Earth is the best and most widely used example of this.

Alongside the centripetal and centrifugal forces, the Coriolis effect is among the most important factors to consider when analyzing a rotating system.

Gaspard-Gustave Coriolis is the French mathematician credited with first proposing this phenomenon in a paper published in 1835. But Riccioli based theories on it back in 1651.

The Italian Jesuit priest/astronomer first made reference to what would later be named the Coriolis effect in an astronomy tome called Almagestum Novum, which listed 77 reason for why Copernicus' heliocentric model of the solar system was wrong.

One of the most important critics of the then-new idea was what Riccioli referred to as an impossibility – namely that the Earth spins around a central axis that drives through its pole.

He set out to demonstrate his idea by proposing a thought experiment, involving a cannon firing from the Equator to the poles. Given that the poles spin slowed than the Equator (in the Copernican model), this would result in the cannonball veering off course.

This was a very solid argument back in its day, coming from an astronomer that had mapped the surface of the Moon. And it still remains a solid argument to this day, until you factor in some new knowledge, Technology Review reports.

The issue with Riccioli's theory is the speed at which the planet rotates. Earth does a full rotation in about 24 hours, which means that the amount of Coriolis effect a cannonball experiences will be very small.

However, more modern analysis techniques are capable of measuring its influence on a variety of objects that are launched in a straight line, most notably bullets and artillery shells.

But the Coriolis effect has a much more important influence in nature, where it dictates hurricane formation. The storms spin due to balance between the Coriolis force and the pressure gradient force.

Christopher Graney, an expert at the Jefferson Community & Technical College in Louisville, Kentucky, was the one who translated Riccioli's arguments from Latin.