Solar System · Newtonian Model
Scale model
Visual scale — sizes & distances compressed so everything is visible.
Physics
Analytic two-body orbits from J2000 elements — exact, stable positions.
Dimension
3D shows real orbital inclinations; 2D flattens onto the ecliptic plane.
Orbit paths Moons heavier Projection lines onto ecliptic Labels
Time · 12.8 days/s
Focus camera
Guided Tour
- 1 What is gravity?
- 2 Gravity builds the Sun
- 3 Gravity builds the Earth
- 4 A moving body keeps moving
- 5 Why the Earth doesn’t fall into the Sun
- 6 Too slow — it falls in
- 7 Too fast — it escapes
- 8 Below orbital speed — it falls back
- 9 First cosmic velocity — orbit
- 10 Second cosmic velocity — escape
- 11 The Earth and the Moon
- 12 Why the Moon doesn’t fall to Earth
- 13 Into the third dimension
- 14 Spinning on their axes
- 15 The Sun moves too — orbits are really helices
- 16 The same forces, still at work
- 17 Moons ride along too
- 18 The whole solar system
- 19 Third cosmic velocity — leaving the Solar System
- 20 The sphere of influence
- 21 Gravity assist — Voyager 1
- 22 Gravity assist — Voyager 2 (the Grand Tour)
- 23 Einstein: gravity is curved spacetime
- 24 The proof: Mercury’s orbit precesses
Step 1 · What is gravity?
Gravity is the attraction between any two masses: F = G · m₁·m₂ / r² — stronger with more mass, weaker with the square of the distance. Here are just two bodies. The arrows show the pull each exerts on the other: exactly equal and opposite (Newton’s 3rd law), about 3.5 × 10²² newtons. The Sun is ~333 000× heavier, so the same force barely moves it but flings the Earth around. This one rule is the whole story — next we’ll see it even built these bodies.