Module 7 · The solar system as a machine
Light, wind and who wins
Interactive 9 min
Light takes 499 seconds, 8 minutes 19 seconds, to reach the Earth from the Sun [1]. The solar wind blows at about 400 km/s [2] and the Earth's magnetic field carves a cavity in it [3]. Around every body is a sphere of influence inside which its pull dominates.
Try this. Watch the wavefront. How long does it take to reach Mars and Neptune? Gravity travels at the same speed as light.
Sources: [1] Astrodynamic Parameters (NASA JPL Solar System Dynamics); [2] Ulysses Begins to Explore Sun's Northern Pole (NASA JPL); [3] Magnetospheres (focus area) (NASA Science)
Step 1 of 3
Eight minutes and nineteen seconds
The solar system is not just big — it is big compared to the fastest thing there is. Light covers 300,000 kilometres every second, and still takes 8 minutes 19 seconds to reach us from the Sun. You never see the Sun as it is; you see it as it was. Watch the wavefront sweep outward: Mars at 12 minutes, Jupiter at three quarters of an hour, Neptune more than four hours out. And this is not just about light. Gravity travels at exactly the same speed. If the Sun vanished this instant, Earth would keep curving along its orbit for another 8 minutes 19 seconds — the news of its absence arriving with the last of its light.
Text version of this interactive
Eight minutes and nineteen seconds
The solar system is not just big — it is big compared to the fastest thing there is. Light covers 300,000 kilometres every second, and still takes 8 minutes 19 seconds to reach us from the Sun. You never see the Sun as it is; you see it as it was. Watch the wavefront sweep outward: Mars at 12 minutes, Jupiter at three quarters of an hour, Neptune more than four hours out. And this is not just about light. Gravity travels at exactly the same speed. If the Sun vanished this instant, Earth would keep curving along its orbit for another 8 minutes 19 seconds — the news of its absence arriving with the last of its light.
The shield around the Earth
The Sun doesn’t only shine — it blows. A million tonnes a second of charged particles stream outward at 400 kilometres a second, and during a solar storm far more. Earth deflects them. Molten iron churning in the core runs a dynamo, and the magnetic field it generates carves a cavity in that wind: squashed to ten Earth-radii on the sunward side, drawn out into a tail far past the Moon behind. Particles that do slip in spiral down the field lines to the poles and light the air as auroras. Mars had a field once, lost it, and the solar wind has been stripping its atmosphere ever since. Gravity holds the air down; magnetism keeps it from being blown away.
The sphere of influence
Whose gravity wins? Around every body is a region — its sphere of influence — inside which its pull dominates. And they nest: the huge solar sphere holds the whole system; inside it Earth carves out its own (≈924,000 km); and inside that the Moon (at 384,400 km) carves out a smaller one still. That nesting is why the Moon orbits Earth rather than the Sun directly — cross a boundary and the next body out takes over. Mission planners exploit this, handing a spacecraft from one sphere to the next as a chain of simple two-body problems.
About this interactive
- Licence
- MIT
- Credits
- © 2026 Mateusz Wojczal. Earth texture: Solar System Scope, CC BY 4.0. Three.js (MIT). Inter and Roboto Mono (SIL OFL 1.1).
- Source
- https://github.com/ulams-dev/ulams/tree/main/demo-content/gravity