Custom Star Map Poster
A poster-ready layout from the start: the sky disc fills the upper three-quarters, your caption sits beneath, and the canvas matches standard frame sizes.
Design your poster
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.
Sizes and themes
- 30×40 cm and 50×70 cm — the two most common European frame sizes off the shelf.
- 18×24 in — the US standard.
- Night theme — white stars on deep navy; striking, ink-heavy to print.
- Ink theme — dark stars on warm paper white; looks like an engraving and is the economical print.
What resolution does a poster need?
Print shops want ~300 dpi. At 50×70 cm that is roughly 5,900 × 8,300 pixels. The free downloads here are a watermarked SVG and a screen-resolution PNG — good for previewing and sharing, not for a wall print. The clean 300 dpi PNG/PDF export is the planned paid upgrade; the button is in the generator, the checkout is not live yet. No pretending otherwise.
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
What file should I eventually take to the print shop?
The high-resolution PNG or PDF once the paid export ships — 300 dpi at your chosen size. Shops accept PDF most readily; PNG at full resolution works everywhere.
Which theme is cheaper to print?
Ink-on-paper, by a wide margin: it's mostly unprinted paper. The navy night theme lays down ink across the whole sheet and looks best on heavier stock.
Can I make a landscape or square poster?
Not in v1 — the three presets are portrait, which is how star map posters are conventionally framed. More formats are on the backlog.