How to use
- Choose the date and local time, then a city or “Use my location”.
- On the right, enter a title and a message and choose a style (midnight blue, black, or ink-saving white) and a size.
- Tick what to show — constellation lines, constellation names, bright star names, the moon and altitude rings.
- Click Download PNG or Download PDF; A4 and Letter are rendered at 300 DPI, ready to print.
Options explained
- What the map covers
- The circle is the horizon and the centre is straight overhead; it shows the stars down to magnitude 6 (about 5,000 in all) that were above the horizon at that moment.
- Orientation
- As seen looking up — north at the top, south at the bottom, east on the left and west on the right — the mirror image of a map.
- Calculation
- Star coordinates are converted to altitude and azimuth for that time and place using sidereal time, with precession; the moon’s position comes from suncalc. Planets are not shown.
Ideas for a meaningful star map
| Occasion | Time | Tip |
|---|---|---|
| A birth | The time of birth, or 9 pm if unknown | A birthday or new-baby gift |
| The night you met | That evening | Use the city where you were |
| A wedding | When the evening ended | Put both names in the title and the date or a vow in the message |
| Graduation, a move, a trip | That night | Use the destination — the sky really is different |
Constellation names follow the 88 constellations of the International Astronomical Union. To see the moon’s phase that night, check the moon phase calendar.
How the place changes the sky
Latitude decides which part of the sky you can ever see. The Pole Star stands as many degrees above the northern horizon as your latitude, and a star never rises if its declination is further south than −(90° − latitude).
| Place | Pole Star | Never rises | Worth knowing |
|---|---|---|---|
| London (51.5° N) | 51° up | South of −38.5° | Canopus and the Southern Cross never appear |
| New York (40.7° N) | 41° up | South of −49.3° | Canopus stays below the horizon; Sirius never climbs above 33° |
| Hong Kong (22.3° N) | 22° up | South of −67.7° | The Southern Cross skims the southern horizon in spring |
| Singapore (1.3° N) | On the horizon | Almost nothing | Nearly the whole sky passes overhead during the year |
| Sydney (33.9° S) | Below the horizon | North of +56.1° | The Southern Cross never sets; only the handle of the Big Dipper rises, low in the north |
That is why a map for a trip abroad looks different from one for home, even on the same night.
How the date and time change it
The stars rise about four minutes earlier each day, so the sky at 9 pm on one date looks like the sky at 11 pm a month earlier. Over a year every season brings its own evening sky: Orion high in the south on winter evenings in the northern hemisphere, the Summer Triangle of Vega, Altair and Deneb overhead in July and August. If you do not know the exact time of an event, the evening hour you remember is close enough — an hour either way turns the sky by only 15°.
How many stars you would really have seen
The map shows every star down to magnitude 6, the limit of the eye under a dark sky: 5,044 over the whole sky in the catalogue used here, so roughly 2,500 above the horizon at any moment. City lights wash most of them out:
| Sky | Faintest star visible | Stars above the horizon |
|---|---|---|
| City centre | Magnitude 3 | About 90 |
| Suburbs | Magnitude 4 | About 260 |
| Dark countryside | Magnitude 6 | About 2,500 |
So a chart for a night in town is the sky as it really was, not as it looked through the glow.
Frequently asked questions
Is it the real sky?
Yes. Star positions come from the XHIP catalogue and are calculated for the date, time, latitude and longitude you enter. The sky differs from city to city at the same moment, so choose the right place. Clouds and city lights mean you would actually have seen far fewer stars.
Why is east on the left?
A map is a view from above; a star chart is a view from below, so left and right swap. Hold the chart above your head with the top to the north and it matches the sky.
Will it print sharply?
A4 is 2480 × 3508 pixels and Letter 2550 × 3300 — 300 DPI — so it prints sharply at A4, Letter or even larger. The square option is 3000 × 3000 pixels, good for social media or a square frame.
Can I use dates long ago?
Yes, from 1900 to 2100. The stars barely move in a lifetime, so the constellations look the same; the slow wobble of Earth’s axis (precession) shifts everything slightly and is included.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.