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Earth, the Sun & the Moon — All Three Moving
The picture neither of this site's other simulators draws: the Earth going round the sun while the moon goes round the Earth, both at once. It is drawn small enough to fit a screen, which means it cannot be to scale — and the card below it says exactly how far out it is.
Drag to tip the whole orbit away from you. It flattens as it goes — wider and shorter — until you are looking along its edge, where the Earth loops in front of the sun and then behind it, and the moon’s tilted orbit visibly misses the sun–Earth line.
The Earth crosses its own big ring once every drawn orbit; watch the Moon and it crosses its small one about thirteen times in that same span — the real ratio between a 27.3-day month and a 365.25-day year, kept even though neither ring is at the real distance. Every dark half faces away from the sun, the moon's grey patch keeps facing the Earth, and the Earth's axis keeps one fixed lean — the four cards below say why each of those is worth staring at.
Four true things hiding in this toy drawing
1 · The lit sides always face the sun. Watch the Earth all the way round: its bright half tracks the sun the whole lap, because day and night are nothing but which half faces the light. The moon's bright half does the same — which leads directly to the strange part.
2 · The moon shows us one face, but the sun lights whichever half it likes. The grey patch on the moon always points at the Earth — the moon genuinely turns exactly once per orbit, so we only ever see one side (that is tidal locking, and why the far side stayed unphotographed until 1959). But its lit half tracks the SUN, not us. Follow one lap: when the moon sits between Earth and sun, the face we see is all shadow (new moon); on the far side, all lit (full moon). Same face, different lighting — that is the whole phase cycle, and you can check tonight's result against the real phase. It is also why "the dark side of the moon" is a misnomer: the far side gets exactly as much sun as the near side.
3 · The axis leans one fixed way — and that lean is the seasons. The Earth's pole is tilted 23.4° and keeps pointing at the same patch of sky all year (toward Polaris). It does NOT swivel to follow the sun — watch the little axis hold its angle through the whole orbit. So on one side of the orbit the north pole leans sunward (June — long days, high sun) and half a year later it leans away (December). Nothing about the Earth changed; only which end leans toward the light. The lean is easiest to see from the side — drag the tilt slider under the picture to tip the orbit edge on, and watch the axis stay parallel to itself all the way round the loop. The seasons lesson turns exactly this into a class period, including why "closer to the sun" cannot be the reason.
4 · Why eclipses are rare — visible from the side. Seen from above, the moon crosses the sun–Earth line twice a month and you would expect an eclipse every crossing. Now tip the orbit edge on with the slider: the moon's orbit is tilted out of the Earth's, so at most new and full moons it slides above or below the sun–Earth line instead of through it. The tilt is drawn steeper than its real 5.1° so you can see it (the scale card below says by how much), but the miss is genuine — the real angle still carries the moon several times its own width off the exact line, which is why eclipses come in occasional seasons and the real list is short. The eclipse lesson is built on exactly this.
This picture is not to scale — by how much
The directions each body turns, and the ratio between the two periods, are real. Every size and every distance is invented, because a drawing that held the Earth's orbit AND the Moon's true distance at once has no room left to show the Moon at all — it would sit closer to the Earth than the line marking the Earth's own edge.
Try it in a corridor. Shrink the Earth to a 16 mm marble. The moon is then a 4.4 mm bead — about a peppercorn — held 48 cm away. The sun is a 1.7 metre ball, taller than a person, standing 188 metres down the road: nearly two football pitches. Nothing about that fits on a screen, so this picture keeps the angles honest and lets the distances go.
What you can trust here: which way each body turns and orbits, that the moon genuinely completes about thirteen trips round the Earth for every trip the Earth makes round the sun, and — with the orbit tipped edge on — that the moon's orbit really does carry it off the sun–Earth line at most new and full moons. What you cannot: any size, any distance, the drawn steepness of that tilt (exaggerated, as the table says), or the direction its crossing line points — a drawing choice, so nothing here says when in the year real eclipse seasons fall.
Common questions
Is this to scale? No, and it says so on the page: every size and every distance here is invented so the Earth's orbit and the moon's orbit can both fit on one screen. What is real is the direction each body turns, the ratio between the two periods, the fixed lean of the Earth's axis, and which half of each body is lit.
Why does the moon go round so much faster than the Earth does? Because it really does: the moon completes an orbit in about 27.3 days against the stars, and the Earth takes 365.25 days to go once round the sun — about thirteen moon orbits to one Earth orbit, which is the speed this page's animation runs at.
Does the same side of the moon always face the Earth? Yes — the grey patch in the drawing marks it. The moon rotates exactly once per orbit, so one face points at us permanently. But the SUN lights whichever half faces it, so the face we see swings from fully dark (new moon) to fully lit (full moon) and back. Same face, changing light: that is what the phases are.
Is the Earth's tilt really why we have seasons? Yes. The axis leans 23.4 degrees and keeps pointing the same way in space all year — watch it hold its angle through the whole drawn orbit. When your hemisphere's pole leans sunward the days run long and the sun stands high; half an orbit later it leans away. Distance is not the cause — the Earth is actually closest to the sun in early January, in the middle of the northern winter.
What does the tilt slider do? It tips Earth's whole orbit away from you, from lying flat and face on to standing edge on. As it tips, the orbit flattens — wider and shorter — until it is a line. Edge on you can see the things a flat diagram cannot show: Earth passing in front of the sun and then behind it, which is the year, and the moon's tilted orbit carrying it above or below the sun-Earth line at most new and full moons, which is why eclipses are rare. Earth's axis keeps its 23.4-degree lean relative to the orbit throughout and tips along with it.
Why isn't there an eclipse every month? Because the moon's orbit is tilted about 5 degrees out of the plane of the Earth's, so at most new and full moons the moon passes above or below the exact sun-Earth line instead of through it. Tip the orbit edge on with the slider and you can watch it happen — the drawn tilt is exaggerated so it is visible at this size, but the miss is real: even 5 degrees carries the moon several times its own width off the line.
Where can I see this to scale? Nowhere on one screen, at both distances at once — that is the whole point of this page. The Earth and the Moon ARE drawn to real scale, in both size and distance, on the Earth & the Moon rung of the solar system simulator; that view has no room left to also show the sun.
How the positions are worked out, and where they stop being reliable: sunrise & sunset, moon phase.