Star Chart

Celestial coordinates

Every star on this chart is placed using the equatorial coordinate system, the astronomer's grid for the sky. Right Ascension (RA) measures east-west position in hours (0–24h, like longitude), while Declination (Dec) measures north-south in degrees (−90° to +90°, like latitude). The celestial equator sits at Dec 0°, directly above Earth's equator. This projection maps the celestial sphere onto a flat plane using a stereographic projection, which preserves the shapes of constellations while allowing you to rotate the entire sky.

How star charts work

A star chart is a snapshot of the celestial sphere — the imaginary dome of sky surrounding Earth. Since ancient times, astronomers have recorded star positions with increasing precision: from Hipparchus's catalogue of 850 stars (circa 129 BC) to the Hipparcos satellite's measurements of over 100,000 stars to milliarcsecond accuracy. The brightness of each star is measured in apparent magnitude, an inverted logarithmic scale where lower numbers mean brighter stars. Sirius, the brightest star in the night sky, shines at magnitude −1.46, while the faintest stars visible to the naked eye are around magnitude 6.

History of constellation mapping

The 88 modern constellations recognized by the International Astronomical Union descend from a long human tradition of finding patterns in the stars. Many of the northern constellations trace back to Mesopotamian astronomers around 3000 BC, later codified by Ptolemy in his Almagest (150 AD) as 48 constellations. European explorers added southern constellations in the 16th–18th centuries to fill the sky visible from the Southern Hemisphere. Today constellations serve not as mystical figures but as a coordinate system — convenient regions of sky that astronomers use to locate and name celestial objects.