The Night Sky on Your Birthday
Somewhere above the delivery-room roof there was a sky. This tool reconstructs it: the exact stars over your birthplace at the moment you were born, as a chart you can caption and print.
Make your birthday 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.
Enter your birth date, birth time (it’s on most birth certificates) and birthplace, and the generator computes which stars were above the horizon at that moment — dot sizes matched to real brightness, constellation figures drawn in, your name and a line like “Born under these stars” beneath.
One honest subtlety: the fixed stars return to almost the same position on the same date and hour every year. What makes a birth sky uniquely yours is the combination of time of night and place — a 3 a.m. birth in New York and a 9 p.m. birth in Tokyo on the same date get very different charts.
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
I don't know my exact birth time — is the map ruined?
No. The sky rotates 15° per hour, so being an hour off rotates the chart a little and swaps a few stars at the horizon; the overall sky is recognisably the same. If the time is unknown, a symbolic choice like 21:00 or midnight works fine — just say so in the caption if you care.
Will my zodiac constellation be on the map?
Usually not — and that's real astronomy, not a bug. Your sun sign is by definition the constellation near the sun on your birthday, so it is up during the day and below (or hugging) the horizon at night. Your zodiac constellation is best visible about half a year away from your birthday.
What should the caption say?
The title is usually the name; common subtitles are “Born under these stars”, “First night sky” or just the date. The place line can be the city or the exact coordinates — the generator can print both.