Space
Where everything actually is, right now. Every planet, a page each, turning on its own axis with its moons going round it — the whole system on its real orbits, and the next launch window to Mars. The positions are solved when the page loads, not drawn from memory.
Why don’t planets fall into the Sun? They are falling. They are also moving sideways. By the time a planet has fallen, the Sun is no longer where it was falling toward. Falling and missing, without end, is an orbit. There is no outward force holding them up.
How does an orbit work? At every instant a planet has a velocity — where it is already going — and gravity adds a small pull straight toward the Sun. Bend a path by the same small amount at every step and it closes. That closed path is the orbit.
Why does Jupiter have so many moons? Gravity’s reach grows with mass, and Jupiter has more of it than anything in the solar system except the Sun. A wide region around it is a place where a small body stays with Jupiter instead of orbiting the Sun on its own.
Where the sun and moon are from your town, at any moment.
The year and the month running at once — and the moon lapping the Earth about thirteen times on the way round, which is the one ratio this picture keeps real. Tip the whole orbit edge-on and watch the Earth loop in front of the sun, then behind it.
The planets where they actually are today.
A picture and a couple of paragraphs for each one, in orbital order, with the asteroid belt where it actually sits and Pluto labelled for what it is — and a page for every one of them, turning on its own axis with its moons going round it.
All the planets, side by side →When the next window to Mars, Jupiter or Saturn opens, how long the flight takes and what it costs in speed — every date solved from the real orbits, and the path drawn so you can fly it.
Rocket launches & launch windows →A circle: falling exactly as fast as the curve carries it away.
Nothing spirals in. Take speed away and the far side of the orbit drops toward the planet; add speed and it climbs away — and either way the moon comes back through the point where you changed it.
Why planets don't fall into the sun →Phobos laps Deimos about 4.0 times over — 7.7 hours against 1.3 days. Orbits, periods and sizes are real; where each moon sits on its ring is not solved here.
2 confirmed moons · 2 drawn
Mars and its moons →Metis laps Callisto about 57 times over — 7.1 hours against 17 days. Orbits, periods and sizes are real; where each moon sits on its ring is not solved here, and 9 further out are off the edge of this frame.
97 confirmed moons · 8 drawn
Jupiter and its moons →Pan laps Hyperion about 37 times over — 14 hours against 21 days. Orbits, periods and sizes are real; where each moon sits on its ring is not solved here, and 8 further out are off the edge of this frame.
274 confirmed moons · 22 drawn
Saturn and its moons →Cordelia laps Oberon about 40 times over — 8.0 hours against 13 days. Orbits, periods and sizes are real; where each moon sits on its ring is not solved here, and 5 further out are off the edge of this frame.
28 confirmed moons · 18 drawn
Uranus and its moons →Naiad laps Triton about 20 times over — 7.1 hours against 5.9 days. Orbits, periods and sizes are real; where each moon sits on its ring is not solved here, and 4 further out are off the edge of this frame. Triton goes round backwards.
16 confirmed moons · 8 drawn
Neptune and its moons →Charon laps Hydra about 6.0 times over — 6.4 days against 38 days. Orbits, periods and sizes are real; where each moon sits on its ring is not solved here.
5 confirmed moons · 5 drawn
Pluto and its moons →Start with a question — why don't the planets fall into the sun, and six more. Or jump across: Home · Time · Earth · Classroom.