Nth Stone from the Sun

Two engines, one sky. Planet positions come from Keplerian orbital elements with linear drift from the J2000 epoch (after JPL's published approximate elements). The Moon can't be treated that way — the Sun's tidal pull constantly reshapes its orbit — so it gets a truncated periodic series of 120 sine terms (Meeus / ELP-2000). Both feed the same transform: ecliptic position → precession to date → RA/Dec → your local altitude and azimuth, with the Moon corrected for the fact that you stand on Earth's surface, not at its center (that alone moves it up to a full degree).

Error bars, honestly. Planet directions are good to roughly 1–10 arcminutes (worst for Saturn near the 1800/2200 edges — still far less than the width of your finger at arm's length). The Moon is good to about 10 arcminutes, a third of its own disk: fine for "look there", useless for predicting eclipses. Moon phase is essentially exact. Rise and set times carry a few minutes of genuine uncertainty — refraction near the horizon depends on the weather that day — which is why they are shown rounded, with a "~". Throughout the app, sharp numbers mean solid values; soft italic ones mean approximate. That convention is the disclaimer.

Why 1800–2200? The element tables are straight-line fits around the year 2000. Planetary dynamics are chaotic on long timescales: outside this window the model doesn't get gracefully worse, it becomes meaningless. So the app refuses to go there.

Reading the charts. The orrery looks down on the solar system from the north, turned so the vernal equinox (ecliptic longitude 0°, marked at the top of the AU ruler) points straight up — that lines it up with the geocentric sphere beside it, which looks edge-on from the 6 o'clock side up toward the equinox, so left and right agree across the two. It offers two honest ways to draw distance. To scale shows real relative distances out to the nth stone from the sun you pick with the − / + stepper: angles and spacing are true, so the Sun–Earth–planet geometry matches what you'd measure in the sky — the price is that the outer planets fall off the edge while you're zoomed in on the inner ones. Power compresses distance as a^0.42 so all eight planets share one screen — every heliocentric angle stays true, the Sun sits at the exact center, but the spacing (and with it the Earth-based angles) becomes schematic. The tap-selected body shows its true distance from the Sun, in AU, in either mode. Sizes are never to scale. The geocentric sphere (earth & moon) is the bridge panel, and it is literally Ptolemy's picture: a small turning Earth inside a big translucent celestial sphere, seen from outer space. The sky has no distances, only directions — so the Sun, Moon, and planets are projected onto that sphere where their directions pierce it. The dashed circle around the sphere's middle is the ecliptic, the road they all travel; the dotted blue one is the celestial equator, Earth's equator cast onto the sky — the two cross at 23.4°, and the crossing marked 0° is the vernal equinox the plan's ruler points to. The equator also crosses your horizon at exactly two points, and they are due East and due West — marked so, for any observer anywhere off the poles: that crossing is what defines east and west in the sky. When you spin the view, a small λ readout on the far side of the ecliptic tells you which ecliptic longitude the camera faces. On the Earth itself you can still see the axis leaning its true 23.4° (the lean, held fixed as we orbit, is what gives us seasons), the sunlit half (the seam is the terminator), and you, riding the spin from day into night. Your straight-up line runs out to a small zenith mark on the sphere, and the bright circle 90° around it is your horizon. That circle is the whole bridge: peel the cap of sphere inside it, lay it flat on a table — and you are holding the dome view below. A body inside the cap — above your horizon — is drawn solid; below it, hollow: the solid ones are exactly what your sky is showing. Each body also gets a dashed line from you — your actual line of sight in space. The Moon here is lit as this outside viewpoint sees it, like the Earth beside it — not the phase you see from the ground, since you and this camera look at the Moon from opposite sides (your phase is in the sky views and the list below). Drag the panel to spin it — parallax makes the 3-D positions read; let go near the home direction and it snaps back in line with the plan. Tap any body to select it everywhere. Directions and lighting are true; sizes and distances are not. The hour / day / month / year chips pick one time unit: the ‹ › arrows jump the clock a single unit per press, ▶ plays at one unit per second, and the shuttle under the clock scrubs — a full push is about 24× that rate — all driving every panel at once. Below, the same instant seen from where you stand. The panorama is an undistorted window on the horizon: pick its width with the − / + chips, from 120° up to the full 360° round (240° holds sunrise and sunset in one frame). Whatever the width, one degree of sky is the same size across and up, so shapes and heights read true — wider simply means smaller, never stretched the way the old full-circle strip was. The frame reaches about 85° up; the zenith itself is the one place a flat strip cannot show honestly — that single point would smear across the frame's whole width — so straight-up belongs to the dome. Drag to spin which direction sits at center. The dome shows the whole sky at once, zenith at the center; drag to rotate it, or tap the compass button and the chart turns so the direction you are facing sits at the bottom — like holding a star chart up in front of you. The dashed curve in every sky mode is the ecliptic, the line along which the Sun, Moon, and planets always travel. Rise and set use the standard upper-limb + refraction convention (Saemundsson's formula). All times are shown in this device's time zone, even for far-away cities.