The sky above you right now — or above any city on any night. The horizon, the compass points, sunset and twilight are worked out for the place you choose; the stars, planets and Moon stand where an eye would see them.
The Milky Way itself is the "Deep Star Maps 2020" panorama by NASA's Scientific Visualization Studio, assembled from the Hipparcos, Tycho-2 and Gaia catalogues: every star's colour and brightness come from measurement. On top of it sits our catalogue: 9096 stars down to sixth magnitude, the figures and official boundaries of all 88 constellations, 333 stars with IAU names and the 110 Messier objects. Tap a star and its card opens; tap empty sky and you get the constellation that point belongs to.
The atmosphere and the landscape are drawn, but not made up: the colour of the sky follows how far below the horizon the Sun is, so in the evening the sunset fades first, then the bright stars appear, and only in full astronomical night the Milky Way. The Sun, Moon and planets are computed in the browser from the astronomy-engine ephemerides for your spot on Earth, precession and nutation included.
On a phone, turn on "Point the phone" and the sky on the screen follows wherever you aim it. The place comes from the browser's time zone without asking for any permission; for an exact one use "My location" or search for a city.
Frequently asked
Why exactly 9096 stars?
That is the complete Yale Bright Star Catalogue — everything brighter than about sixth magnitude, which is precisely what an unaided eye separates on a dark night. The closer you zoom in, the fainter the stars that appear, as in binoculars.
Why is the distance of some stars given as a range?
Distance is measured by parallax — the tiny shift of a star against more distant ones over half a year. The further the star, the smaller the shift, and for the most distant it becomes comparable to the measurement error. Deneb's parallax carries a 56 per cent uncertainty, so a range is the honest answer.
How accurate are the planets and the Moon?
To a fraction of an arcminute: the astronomy-engine ephemerides rest on the VSOP87 and ELP theories, and the Moon is corrected for where on Earth you stand — up to a degree near the horizon. Atmospheric refraction is left out: right at the horizon the bodies actually appear about half a degree higher.
Where did the star atlas and the planetarium go?
They became this section. Every star, constellation and Messier page is still here with the same address, only inside the Sky; the old links lead here.
A constellation is not a group of related stars but a region of sky. Since 1930 the International Astronomical Union has divided the celestial sphere into 88 areas bounded by lines of constant right ascension and declination, and every point of sky belongs to exactly one of them. That is why tapping empty sky always finds a constellation.
A star's apparent brightness says almost nothing about the star. Sirius looks brightest only because it is eight light years away, while Deneb, thousands of times more powerful, barely makes the top twenty because it is hundreds of times further off. On each star's page its place on the Hertzsprung-Russell diagram shows what it really is.
Sources
Positions, magnitudes, spectra and proper motions come from the Bright Star Catalogue, 5th ed. (Hoffleit & Warren, 1991). Distances use Hipparcos parallaxes (ESA, 1997): BSC5's own parallaxes predate the satellite and give negative distances for the far stars. Constellation boundaries are Davenhall & Leggett (1989), precessed here from B1875 to J2000. Star names are the official catalogue of the IAU Working Group on Star Names (CC BY). Accessed through the VizieR service, CDS, Strasbourg.
Panorama: NASA/Goddard Space Flight Center Scientific Visualization Studio, Deep Star Maps 2020 (public domain). Catalogues: Bright Star Catalogue, Hipparcos, IAU-CSN, NGC 2000.0. Ephemerides: astronomy-engine. Cities: GeoNames (CC BY).