Where everything is tonight

The planets come from JPL’s Keplerian elements for approximate positions of the major planets, which is six elements and six rates per planet, fitted over 1800 to 2050. JPL says plainly that they are “not valid outside the given time-interval”, so the clock refuses to leave it — it stops at both ends of the scrub rather than carrying on into a century nobody fitted. Inside it, the published error runs from 15 arcseconds of heliocentric longitude for Mercury to 600 for Saturn, which at the scale of this figure is under a pixel for every planet on it.

The 24,045 asteroids and comets behind them come from JPL’s Small-Body Database, which publishes each object’s elements osculating at one epoch — a snapshot of the orbit it is on today rather than a fit across two centuries. Scrub far from that epoch and the belt is telling you the shape of the solar system rather than the position of any one rock in it.

24,045 of the catalogue’s 26,415 small bodies are on the figure, and the difference is not a gap in it. 2,309 comets are on open orbits, which have no closed path to put a body on — a negative semi-major axis is the element doing its job. Everything that is here turns anticlockwise seen from the north, which is the direction the solar system turns.

Drag the figure, or press the arrow keys, or take one of the three presets. Pole is the view every diagram of the solar system is drawn in, straight down the ecliptic’s north pole. Edge is the one that shows what that view is hiding: seen from within the plane, the eight planets collapse onto a line about seven degrees thick, and everything that does not is the point — Pluto seventeen degrees out of it, Halley going round the other way at a hundred and sixty-two, and the belt revealed as a torus rather than a ring.

The positions were always three-dimensional — every body here publishes a longitude of the ascending node, which is more than can be said for the exoplanet system figures on this site, drawn perpendicular to their orbital plane because their catalogue publishes that angle for not one planet in it. What this page used to do was compute all three coordinates and then throw the third one away at the last step. It no longer does.

The projection is orthographic rather than perspective, which is a decision and not a shortcut: nobody has ever stood anywhere that the solar system looks like a perspective drawing from, and a perspective camera would make the scale bar a lie. Here a horizontal distance on the screen is exact at every angle the figure can be turned to. What tilting costs is the vertical, foreshortened by the sine of the tilt, exactly as it should be.

The radial scale is linear, as it has to be: a logarithmic radius turns an ellipse into a shape that is not one, and the shape is what tells you that Halley and Venus are not the same kind of object. So the way in is the field control rather than a distorted axis, and each step in drops the outermost orbit.

The belt above is a shape until something tells you where its edges are. Main belt, Trojans and Kuiper each draw one region in the plane of the ecliptic and light the bodies inside it, and the test that decides which those are is the orbit and nothing else: a semi-major axis between 2 and 3.2 astronomical units with a perihelion outside 1.666 for the main belt, which is the boundary that separates a belt asteroid from a Mars-crosser; 4.6 to 5.5 astronomical units on a nearly circular orbit for the Trojans; 30 to 50 for the Kuiper belt. Those are the same boundaries the Small-Body Database classifies its own rows by, so the count printed beside a region is a count of what is drawn rather than a figure quoted from somewhere else.

The Trojan clouds are the one annotation that moves while the clock runs. They are sixty degrees ahead of and sixty degrees behind Jupiter — not sixty degrees from a fixed direction in space — so they are drawn from wherever Jupiter is at the instant on the clock, and scrubbing a century moves them with it.

The bodies do not keep up with the arcs, and that is a limit of the model rather than a fact about the sky. Every small body here is moved on its own two-body orbit around the Sun; what actually holds a Trojan sixty degrees from Jupiter is Jupiter, and a pull from one planet on another body is not in that calculation. Each of them runs at its own period instead — a spread of about five per cent across the group — so within a century of clock time the two clouds have sheared out into a plain ring, and only the arcs still mark where they belong. Today, and for a few decades either side of it, the clouds are where the catalogue says they are.

Moons draws every satellite the catalogue can place at its own planet, at the same scale as everything else — which is why the switch says none are drawn until you come in. From a field wide enough to hold the outer planets, every satellite system in the solar system is smaller than the dot its planet is drawn as: the Moon’s whole orbit is a third of a pixel. Ask about a planet and the ladder continues past its last rung into that planet’s own system, and the frame goes with it — the arithmetic stays measured from the Sun, and the picture is pointed at the planet, because a picture of the Earth and its Moon centred on the Sun is a picture of neither.

A moon’s orbit is about its planet, so it arrives in a different form from everything else here: a size, a shape, and the plane the angles are measured in — and that plane is not always the same one. The outer, captured moons are given in the plane of the Earth’s orbit; the Uranian and Plutonian ones in their planet’s equator; the close-in regular moons in a third plane again, the one a nearby orbit is forced into by the planet’s own bulge and the Sun pulling together. Titan’s plane leans twenty-seven degrees out of the ecliptic because Saturn does. Read in the wrong plane a moon still goes round the right planet at the right distance in the right time, and is simply in the wrong place — so each row carries the name of its plane and that plane’s pole, and both are on the moon’s own page.

Two numbers those tables leave out are how fast a moon’s orbit turns in its own plane and which way — the published figures give the size of each drift and not its direction, and the two readings put a moon on opposite sides of its planet within a decade. Io’s and Europa’s turn one way and Ganymede’s and Callisto’s the other, because the inner two are held in a resonance the outer two are not. So the catalogue measures all of it against the ephemeris itself, and every moon carries how far the result sits from that ephemeris at the worst of four dates across a decade. The Galileans agree to a tenth of a degree and the Moon to a degree and a half; a moon whose orbit cannot be pinned closer than fifteen degrees is left out of the picture rather than drawn as confidently as one that can.

Frost line is the exception, and it is drawn dashed for the reason it is drawn at all. Every other ring on this figure is a boundary in a table of orbits; that one is about 2.7 astronomical units out, where models of the disc the planets formed from put the temperature at which water stops being a gas. Nothing in this catalogue measures it. It is here because it is the reason the four planets inside it are rock and the four outside it are not, and the label says it is modelled rather than measured. Ecliptic puts circles and thirty-degree spokes under everything, so a distance on the picture can be read instead of guessed — which is the same job the bar in the corner does for one length.

Oort cloud is the other exception, and a larger one. Nothing out there has ever been seen: the cloud is inferred entirely from where the long-period comets come in from, and the two boundaries drawn — roughly 2 000 and 100 000 astronomical units — are the range that inference gives. It is drawn as a circle rather than a ring in the plane, and stays a circle when the figure is turned edge on, because a shell seen from any direction is a circle; drawing it flat would claim the comets arrive along the plane, which is the one thing their orbits say they do not. What is real in it is the comets: the ones lit are those in this catalogue whose orbits reach beyond a thousand astronomical units, and their aphelia are the whole of the evidence that anything is out there.

Comets grow a tail as they come in and lose it again on the way out, so the figure draws one only inside about five astronomical units, longest at perihelion, and points it away from the Sun rather than backwards along the orbit — the tail is blown off the comet by sunlight and the wind coming with it, so on the way out a comet follows its own tail. Run the clock to February 1986 and Halley has one; run it to now and it does not.

Flybys on the control bar lists the 38 near-Earth asteroids passing inside twenty lunar distances in the published window, and picking one moves the picture from beside the Sun to beside the Earth. That is a different picture rather than another step of the field control: everything a close approach is about happens inside the dot the Earth is drawn as up there, so the flyby view starts again with the Earth at the middle, kilometres instead of astronomical units, and the Moon’s own orbit drawn at the same scale as the pass. The clock runs from 5 days before the closest approach to 5 days after it, and the distance in the corner counts down in both units as the thing comes in.

The Moon is there to be measured against. Every one of these passes is quoted in lunar distances — (2026 PC6) comes closest in this window, at 0.053 of one — and a reader cannot check a lunar distance against nothing. Where a pass is twenty lunar distances out the Moon’s orbit is a small ring near the middle of the frame, and that is what twenty lunar distances looks like.

Every other position on this page is worked out in your browser from published orbital elements. A flyby cannot be, and the reason is the one thing worth knowing about this view. An orbit is a two-body answer, and it is a good one only while one body is doing the pulling. Inside the Earth’s neighbourhood neither is: the region where our gravity wins over the Sun’s reaches about four lunar distances, so an object crossing this picture spends the hours that matter where the two are comparable and no ellipse around either one is right. Propagating from elements through that misses the miss distance by thousands of kilometres, which is a large part of the number the whole view is about. So the path is read from NASA/JPL Solar System Dynamics instead — the same integration the published distance itself came out of, sampled at 113 instants across the ten days — closely spaced at the moment itself and widely at the ends, because the thing crosses a lunar distance in five hours — and committed as it stood on 2026-08-30. What runs between two of those instants is a curve through both positions and both velocities rather than a straight line.

Two things about a pass are uncertain and they are not the same thing. The distance is published as a three-sigma range, and for most of these it is narrow enough to disappear into the rounding. The moment is a separate figure, and for an object found last month and seen for a fortnight it can be days wide — in which case the whole path slides by that much and the view says so on the picture rather than in a footnote. Neither is a defect in the drawing: the path is the same solution the numbers came out of, so where the solution is loose the picture is loose in exactly the same way.

None of this is a warning. A pass at these distances is ordinary — it is the reason the survey telescopes exist and the reason the object has a number at all, not a reason to worry about it. What the view is for is the thing a headline cannot do: showing you that the passes on that list run from 0.053 of the Moon’s distance to 20 times it, and letting you turn one over to see which side of us it went.

The named bodies and their orbits are SVG, rendered on the server: they are in the HTML, they are there with JavaScript switched off, and a crawler reads them. The 24,045 small bodies behind them are not, and cannot be — each one has to be moved every time the clock ticks or the view turns, and moving one means solving Kepler’s equation for it. That is Newton’s method, three or four iterations, on twenty-four thousand entirely independent bodies, sixty times a second.

Where the browser has WebGPU, that happens on the graphics card: the elements are uploaded once and every frame after that costs a sixty-four-byte write for the clock and the camera. Where it does not — roughly a fifth of browsers — the same arithmetic runs in JavaScript and the belt is drawn on a 2D canvas instead. The figure says which one it used. Nothing else on the page depends on the answer.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune — and, past them, the named small bodies the figure draws: Apophis, Bennu, Ryugu, Eros, Encke, Vesta, Ceres, Pallas, 67P, Halley, Pluto, Haumea, Quaoar, Makemake, Eris, Sedna. Each has a page with its own measurements, and every element this figure moves it by is on that page.