Home › Astronomy
Everything else on this site is a table; this page is the sky itself. Choose a place and a time — or press play and let time run — and see the Sun, the Moon at its true phase, all eight planets and 493 named stars where they actually are. Below, the same moment drawn from above the solar system, so you can watch an opposition line up.
The dome is the sky over your head: north at the top, the center is the zenith, the rim is the horizon. East is on the left — as it is when you lie back and look up. Days play out too: run time forward and watch the sky wheel, the Moon change phase, and the planets drift.
Orbit sizes are compressed (square-root scale) so Mercury and Neptune fit on one screen; positions around the orbits are true. An opposition is the moment a planet, Earth and the Sun fall on one line, with Earth in the middle — set the date to a Sky Events opposition and see it.
Every position on this page is computed in your browser, at the moment you look at it, with the same mathematics as the rest of the Almanac — nothing is a pre-drawn animation.
The dome. Star positions come from the Yale Bright Star Catalog (the 493 stars that carry proper names). Each star's right ascension and declination are converted to altitude and azimuth for your place and the simulated time, using the local sidereal time; the chart then projects the sky stereographically — the zenith at the center, the horizon as the rim. The Moon is placed by the lunar series used across this site (the one cross-checked against published full-moon times to a few minutes) and drawn at its true phase: the lit limb and the terminator ellipse follow the actual Sun–Moon angle. Planets use the JPL approximate Keplerian elements — the same engine that put Jupiter's opposition on the exact published day.
The orrery. The second chart plots the planets' true heliocentric positions for the simulated instant, on their real elliptical orbits. Because Neptune is 78 times farther from the Sun than Mercury, distances are drawn on a square-root scale; angles around the Sun are exact, which is what conjunctions and oppositions are made of.
Things to try. Set the place to your home, press play at one hour per second, and watch tonight wheel past. Jump to 12 August 2026 and find the geometry behind the total solar eclipse. Set the orrery to 10 January 2026: Sun, Earth and Jupiter stand in a line — that is Jupiter's opposition, the first entry of the Sky Events year.
As accurate as the Almanac behind it: the Moon to a few arcminutes, the planets to a fraction of a degree — more than enough to find everything with binoculars. It is a finding and learning instrument, not a telescope mount driver.
Because the chart shows the sky as you see it when you look up. A map of the ground has east on the right because you look down at it; turn the map over your head and east and west trade places. All printed star atlases draw it this way.
That is retrograde motion, and the simulator shows it honestly. When Earth, moving faster on its inside orbit, overtakes an outer planet, the planet appears to loop backwards against the stars for a few weeks around opposition. Watch Mars in the orrery while the dome runs, and the cause is obvious.
The geometry, yes: set a place in Iceland or Spain, the date to 12 August 2026, and run the morning — the Moon (drawn at its true size on the chart is exaggerated, but its position is real) crosses the Sun. The page does not darken the sky for the eclipse itself.