About this sky

Positions. Every planet direction comes from the astronomy-engine ephemeris (with light-time and aberration corrections), accurate to about one arcminute — far below anything visible at these zoom levels. Stars are real HYG catalog positions; constellation figures and boundaries are the standard open datasets. Everything shares one consistent sky, so conjunctions and alignments are real.

Every number you can read. Degrees and signs are true tropical (equinox-of-date) longitudes — the same values a chart would use. Daily motion, retrograde status, ingress timings, distances, magnitudes, illumination, and moon phase are all computed live, never canned. The aspects on each planet's panel are true geocentric separations measured against the standard orbs (8° conjunction/opposition, 7° square/trine, 4° sextile).

Light and phase.Each globe is lit along its true Sun-to-planet direction in real space, so Venus shows a genuine crescent and the Moon's phase matches the real sky. The Moon is tidally locked — the near side you see is the near side. Planets spin at their true sidereal rotation periods (Venus and Uranus backwards, as in reality), and each spin axis points at its true celestial pole — including Saturn's rings, which open and close over the years exactly as seen from Earth.

Comets and meteors. Comets follow their published JPL orbital elements, and their brightness on screen follows the standard photometric model from JPL's parameters — a telescope-only comet is a faint mark here too. Meteor shower radiants and activity windows are real catalog data.

Size, by default. At true scale, every planet is an invisible dot — Jupiter is roughly 100× smaller than we draw it. The default view stylizes sizes so the sky is usable (they do swell and shrink with real distance). When two bodies crowd each other — a close conjunction — both shrink toward their true sizes until the pair resolves, so an event like the 2020 great conjunction looks the way a telescope saw it: two distinct discs, the nearer one in front. Turn on True apparent sizes in the Layers panel to see the honest sky: the Sun and Moon at their real half-degree, planets as the points they truly are.

Depth. Directions are true; distances are not rendered — everything is projected onto one celestial sphere, as in any planetarium. Zooming narrows your view like a telescope; it never travels through space.

Glow.Star sizes follow magnitude on a perceptual curve, but halos, atmospheric rims, the solar corona, and comet tail lengths are artistic. Surface textures are real imagery, though which meridian faces you at a given moment is not calibrated (except the Moon's).

Your vantage point.The sky is geocentric — computed from Earth's center, with no horizon, location, or atmospheric refraction yet. The largest consequence is the Moon, which can shift up to a degree for an observer on the surface. Location-aware skies arrive with birth charts.

Comet orbits. Comets are propagated by two-body Kepler motion from current elements — excellent near the present, slowly drifting for dates decades away, since planetary tugs are not integrated.

Aspect readings. The angles behind each aspect are computed; the one-line interpretations beside them are editorial — our own wording of the traditional meanings, not something derived from the sky.

The clock in the corner jumps the whole sky to any instant between the years 1600 and 2400. Those bounds are honest ones: our ephemeris (astronomy-engine) holds its best stated accuracy from roughly 1700 to 2200 and degrades gracefully beyond, and its Pluto model is tabulated for years 0–4000. Star positions are fixed at epoch J2000 with no proper motion applied — imperceptible over a few centuries, wrong over millennia. Comets drift furthest: two-body propagation from present-day elements loses meaning decades from now, so treat distant-date comets as sketches. Meteor shower dates are the modern catalog; historic showers drifted and some did not exist. All dates use the Gregorian calendar, including years before a given country adopted it.

Ephemerides: astronomy-engine (MIT). Stars: HYG database (CC BY-SA). Constellation data: d3-celestial (BSD-3). Comet elements and photometry: JPL Small-Body Database (public domain). Planet textures: Solar System Scope (CC BY 4.0). Full attributions ship with the app's data files.