Free Star Map Generator — Night Sky on Your Birthday

Generate a beautiful star map showing the exact night sky on any date. Perfect personalized gift for birthdays, anniversaries, and special moments.

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This is a real reconstruction of the sky at a specific moment and place, not a decorative background dotted with stars. Every star, the Sun, the Moon, and the planets are placed by actual position-astronomy: we compute the Local Sidereal Time from the Julian Day and your longitude, convert each object's celestial coordinates (right ascension and declination) into altitude and azimuth for your exact latitude, and drop everything below the horizon (altitude ≤ 0°) — because a "night sky" map that shows stars which weren't actually visible from that spot isn't honest astronomy, it's wallpaper.

The projection itself is azimuthal: the zenith (straight overhead) sits at the centre of the circle, the horizon forms the outer edge, and each star's radial distance from the centre is proportional to 90° minus its altitude. That is the same style of projection used on printed planispheres — it is chosen because it maps the dome of the sky onto a flat circle the way you'd actually tilt your head back and look up, not because it is the only mathematically valid choice.

The Sun and Moon get their own dedicated position calculations (mean-orbital approximations accurate to a fraction of a degree — well within what a keepsake image needs); the planets are placed using the same Swiss Ephemeris engine that runs every birth chart on AskSoma. Everything else on the map is drawn from a curated catalog of the sky's brightest naked-eye stars, connected into their traditional constellation outlines.

What actually determines a star's position on your map

Local Sidereal Time (LST)

Computed from the Julian Day of your chosen date/time and your longitude. LST is essentially "what part of the celestial sphere is currently facing your meridian" — it is the single number that makes the same star appear in a different part of the sky depending on the hour, even from the identical location.

Right ascension & declination

Each catalog star's fixed celestial coordinates — its permanent address on the sky, independent of time or location. The Sun and Moon's equivalent coordinates are computed fresh for your exact moment from their own orbital positions.

Hour angle = LST − RA

How far a given star has rotated past your meridian at this moment. This is the bridge between "where the star permanently is" (RA/Dec) and "where it appears from here, right now" (altitude/azimuth).

Altitude (the spherical-trigonometry step)

Derived from declination, your latitude, and the hour angle via the standard horizontal-coordinate formula. Below 0° altitude, the object is under the horizon and is correctly omitted — this is the step that makes the map honest about what you could actually have seen.

Radial position on the printed circle

Distance from centre ∝ (90° − altitude): objects near the zenith cluster near the middle, objects near the horizon sit near the rim. Azimuth sets the compass direction around the circle.

Computing Local Sidereal Time by hand — the step every star position depends on

1. The formula: GMST (Greenwich Mean Sidereal Time, in degrees) = 280.46061837 + 360.98564736629 × (JD − 2451545.0) + a small quadratic correction for centuries elapsed since J2000.0 — then Local Sidereal Time = GMST + your longitude (east positive).
2. Worked for a round date: at Julian Day 2451545.0 exactly (J2000.0, 1 Jan 2000, 12:00 UTC) the first two terms give GMST ≈ 280.46°. At longitude 77.2° E (New Delhi), LST ≈ 280.46 + 77.2 = 357.66°, i.e. just under a full rotation (360°) — meaning the celestial meridian near right ascension 0h was almost exactly overhead at that instant from that longitude.
3. That single LST value then feeds every star on the map: each star's hour angle = LST − (its own RA), and the altitude formula above turns that into "above the horizon and where" or "below the horizon, omit."

The sidereal-time step is exact arithmetic, not an approximation dressed up as one — you can reproduce GMST for any date with the formula above and a calculator.

What this tool can NOT tell you

• The star field is a curated catalog of roughly the sky's 45 brightest naked-eye stars connected into their traditional constellations — not a full astronomical catalog of thousands. It is built for a beautiful, recognisable, and honest keepsake image, not for locating a faint deep-sky object.
• The Sun and Moon positions use accurate mean-orbital approximations (good to a fraction of a degree) rather than the full perturbation series Swiss Ephemeris runs for birth-chart planets — more than precise enough for a night-sky image, not the standard we'd use for a chart calculation.
• This tool draws the geometric sky — it does not model atmospheric refraction, twilight brightening, cloud cover, or light pollution. A star plotted just above the horizon may not actually have been visible to the naked eye at that location on that night.
• This is astronomy, not astrology: the star map shows what was physically overhead. It carries no interpretive meaning on its own — if you want the astrological reading of a birth moment, that is the birth chart calculator, not this tool.

Computed with Swiss Ephemeris, Lahiri ayanamsa · Content reviewed 2026-08-08