Custom Star Map — the Night Sky for Any Moment
A custom star map shows exactly which stars stood over a particular place at a particular moment — a wedding, a birth, the night you met. This generator computes it from a real star catalog, free, entirely in your browser.
Make your custom star map
Free, in your browser — no account, nothing uploaded. Both downloads are the complete chart: a vector SVG and a 300 dpi PNG, with nothing held back and nothing to buy.
You pick the date, the time and the location (start typing a town name and pick it, or enter exact latitude and longitude). The chart then shows every star brighter than magnitude 5.0 that was above the horizon at that instant — typically 400–900 stars depending on season and latitude — plus the constellation figures connecting them, with your own title and caption beneath the sky disc.
Unlike a decorative print with a random sky on it, this chart is computed with standard positional astronomy — the same math planetarium software uses. Move the time by one hour and the whole sky rotates fifteen degrees, exactly as it did that night.
What you can customize
- Moment — date and time to the minute, any Gregorian date.
- Place — type a town or city and pick it from the list (29,919 places of 18,000 people or more), or enter exact latitude/longitude.
- Caption — title, subtitle and place line (names, a dedication, coordinates).
- Theme — deep-navy night sky, or an ink-on-paper look that is cheap to print.
- Poster size — 30×40 cm, 50×70 cm or 18×24 in, portrait.
- Details — star labels, altitude/azimuth grid, stereographic or linear projection.
How the map is computed
You give it three things: a date, a time, and a place. For the place, type a town or city name and pick it from the list — 29,919 towns and cities of 18,000 people or more, from GeoNames — or enter an exact latitude and longitude instead. Accents are optional (“malmo” finds Malmö), but type the name on its own: “Roskilde Denmark” finds nothing, and a typo finds nothing rather than the wrong sky.
Your date, time and place are converted to a Julian Date and then to local sidereal time — the astronomer’s clock for “which way is the sky facing.” Each of the 1,630 stars in the Yale Bright Star Catalogue (every star brighter than magnitude 5.0, i.e. every star a good naked eye can see) is transformed to its altitude and azimuth at that exact moment, and every one of those stars above the horizon is projected onto the circular chart: zenith at the centre, horizon at the rim, north at the top — and east on the left, because a star map is read looking up, which mirrors east and west compared to a ground map.
The 89 constellation figures are drawn with the same math and clipped at the horizon. Star dots are scaled by real brightness (magnitude) and tinted by star colour. The Moon is drawn at its real altitude, azimuth and phase for your moment, and left off entirely when it was below your horizon. It does not show the planets, comets or satellites — those wander against the fixed stars and need ephemerides, which this version does not compute. Everything runs in your browser — nothing is uploaded, there is no account, and the page works offline once loaded.
Common questions
Is the map astronomically accurate?
For the stars, yes: the pipeline is Julian Date → sidereal time → per-star altitude/azimuth, using the Yale Bright Star Catalogue. It is verified against known reference values (44 automated checks). The Moon is drawn too, at its real altitude, azimuth and illuminated phase; the planets, comets and satellites are not drawn. Star positions are epoch J2000 — a drift far too small to see on a print for dates within a couple of centuries of today.
Can I print it?
Yes, and the file is built for it. The SVG is vector, so it has no resolution to run out of at any poster size; the PNG is rasterized at 300 dpi for whichever page size you chose — 50 × 70 cm comes out at 5906 × 8268 px, which is what a print shop asks for. Both are free and complete. There is no PDF export yet.
Do I need an account? Is anything uploaded?
No and no. The page is static; the astronomy runs client-side in JavaScript. Your dates and places never leave your browser.