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. Free downloads carry a small watermark; a clean high-resolution print export is planned as a paid upgrade.
You pick the date, the time and the location (a city preset or 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 — ~40 city presets, or 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
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. everything a good naked eye can see) is transformed to its altitude and azimuth at that exact moment, and everything 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. 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). It does not draw the moon or planets, and 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?
You can download a free SVG and a screen-resolution PNG, both with a small watermark. A clean ~300 dpi poster file (PNG/PDF) is planned as a paid export — the button exists but checkout is not live 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.