Birthday Star Map
Make a print-ready star map of the sky on any date and place — a birthday, an anniversary, the night you met. Computed from real star positions, free, with no watermark and no sign-up.
A real sky, not a decoration
Most star map posters sold online are generated from the same calculation this page runs, then priced between £40 and £100 with a frame. There is nothing wrong with buying one — but the underlying map is not the expensive part, and there is no reason it should be behind a checkout.
Every dot here is a catalogue position taken through the full chain: local time to UTC using the correct historical daylight-saving rules, UTC to sidereal time, precession to the equinox of that date, then a projection onto the disc. Change the time by two hours and the whole sky rotates 30°, because that is what it actually did.
The Moon is drawn at its real position with its real phase for that night, and the naked-eye planets appear where they were. On 21 December 2020 you will find Jupiter and Saturn touching — the closest they had come since 1623.
Getting the details right
- The time matters more than the date. The sky turns 15° an hour. If you are marking a birth, the time on the certificate gives you the sky that was genuinely overhead; if you do not know it, 22:00 is a good default for a night sky.
- Use the place, not your place. Latitude decides which half of the sky is above the horizon. A map for a birth in Auckland looks nothing like one for Oslo on the same night.
- Daylight saving is handled. The zone database knows the rules that were in force on that date, including ones that have since been abolished — so a July date and a January date in the same city are anchored correctly.
- Star density is taste, not accuracy. Countryside or dark sky gives a fuller, more dramatic print; city centre gives a sparse, graphic one. All four are honest depictions of what that sky looks like under those conditions.
- Check the twilight note. If it says Daylight, the stars in your chart were genuinely above the horizon but invisible behind the Sun. Still a true map — just worth knowing.
Printing it
Sizes and resolution
The PNG is 2000 × 2828 px, which is 240 dpi at A3 and comfortably over 300 dpi at A4. The proportions follow the A series, so nothing is cropped at any of those sizes. For anything larger than A3, use the SVG — it is resolution-free.
Paper and theme
Dark themes look best on matte or lightly textured paper; gloss makes a large black field show every fingerprint. If you are printing at home, Ink on paper inverts the chart to dark stars on cream and uses a fraction of the toner.
Framing
The caption sits well inside the trim, so a standard mount will not clip it. If you want a wider border, add the margin in the frame rather than scaling the image down.
Wording
Title, subtitle and an optional message are all yours to set. Leave the message blank and the moon phase and star count take its place, which suits a map made as a record rather than a gift.
Dates worth trying
The obvious ones are a birth, a wedding, or the night two people met. Less obvious, and often better as a gift, are the ones with something actually happening in the sky:
- 21 December 2020 — the great conjunction. Jupiter and Saturn appear as a single point, closest since 1623.
- 27 July 2018 — the longest lunar eclipse of the century, with Mars at its closest opposition since 2003 right beside it.
- Any night in mid-August — the Perseid radiant sits high in Perseus, in the northeast after midnight.
- A date from the southern hemisphere — set the place to Sydney or Santiago and the sky is unrecognisable: the Southern Cross, the Magellanic region, Orion upside down.
Looking for tonight instead?
This page is built for a fixed moment you want to keep. If the question is "what can I see out of my window right now", the live night sky map defaults to your location and the current time, and lists each planet with its altitude and compass direction.
Accuracy and sources
| Object | Method | Typical error |
|---|---|---|
| Stars | Catalogue positions, IAU 1976 precession | Sub-arcsecond |
| Sun | Low-precision solar theory | Better than 0.02° |
| Moon | Orbital elements plus main perturbations | A few arcminutes |
| Planets | Keplerian elements with giant-planet perturbations | Arcminutes; up to ~0.3° for Jupiter and Saturn |
For scale, 0.3° is about half the width of the full Moon and roughly two pixels on this chart. The star positions — which is what a chart is mostly made of — are limited by the printing rather than the mathematics.
Star, constellation and Milky Way data derived from the d3-celestial datasets by Olaf Frohn (BSD 3-Clause), which draw on the HYG database compiled from the Hipparcos, Yale Bright Star and Gliese catalogues. Algorithms follow Jean Meeus, Astronomical Algorithms, and Paul Schlyter's orbital element compilation. Everything runs in your browser — no date, location or image is sent anywhere.