Spheres of Eudoxus Model

Spheres of Eudoxus Model is a cool Java app that helps you understand how the Ancient Greek astronomer Eudoxus explained the motion of planets. It’s all about showing how he thought they moved in space!

How the Model Works

This model has four spheres that fit inside each other, like a set of Russian dolls. Each sphere spins around an axis that's attached to the next outer sphere. The planet is on the surface of the innermost (red) sphere, while the outermost (white) sphere rotates like our stars do every day.

Adjusting Spheres with Sliders

The Spheres Frame lets you see all four spheres together. You can use a slider to tilt the inner red sphere compared to the middle blue one. The red sphere spins at a constant speed (+1.0, but we don’t have to worry about units). You can change how fast the blue and green spheres rotate using their sliders too!

The Importance of Axis Alignment

Here’s something neat: the blue sphere's axis is connected to the equator of the green sphere! This detail is super important for understanding Eudoxus's ideas. The green sphere's equator lines up with what we call the plane of the ecliptic. And yes, that white outer sphere? It represents what we call the Celestial Sphere filled with fixed stars.

Observing Planet Motion

The Sky View Frame shows how planets move against those stars from Earth’s perspective, which sits right in the middle of these concentric spheres.

Eudoxus and Retrograde Motion

You can tilt that red sphere relative to blue, spin it in opposite directions, and slow down that green one just right. When you do this, you'll see how Eudoxus managed to explain retrograde motion—the way planets seem to go backward sometimes—using his model!

If you're interested in exploring more about this fascinating model, check out this link for more details: Download Spheres of Eudoxus Model.