Sky¹

The sky over one place, at one instant, drawn from the ground: the whole dome, south at the bottom, every star the eye can see, the Milky Way, the sun, the moon and the planets at their computed places. It starts over Tampa, now. Press g and stand anywhere — click the globe or name a city — and the horizon follows. Drag the rail through five thousand years and the sky turns with the earth's slow wobble, so the pole star of 2800 BCE is Thuban; scrub the date and the hour on the readout and the sky rolls over. As the years pass, the record arrives where it was found: a guest star in Taurus in 1054, Galileo's moons in 1610, Herschel's planet, a hiss from Sagittarius in 1932, a pulsar in 1967, the shadow of a black hole — each drawn with the mark of the instrument that found it, eye to gravity. Click one and the eyepiece opens; stand where they stood, and the page takes you to that place on that night. The second tab, Time, lays the whole record out as one page.

¹ Positions are J2000 turned by one matrix: precession to the date (Meeus), sidereal time, and the observer's latitude and longitude. Proper motion is not applied, so the oldest skies are a degree or so soft. Planets from JPL's long-span Keplerian elements; the moon from Schlyter's series. Calendar dates are proleptic Gregorian; the clock is local mean time, the sun's own.

Stars: HYG via d3-celestial (5,044 to magnitude 6) · figures, isophotes and bright deep-sky objects: d3-celestial · coastlines: Natural Earth, through Ceiling · cities: Open-Meteo / GeoNames.