Star Map Viewer

What is a Star Map?

A star map (or sky chart) is a projection of the celestial sphere onto a flat surface, showing which stars, constellations, and planets are visible from a given location at a given time. This tool computes the positions of celestial objects using astronomical algorithms and renders them on an interactive chart.

How to Read the Chart

• Center represents the zenith (directly overhead)
• Edge represents the horizon
• North is at the top, East is on the left (as seen looking up at the sky)
• Star sizes indicate brightness (larger = brighter)
• Lines connect stars in recognized constellation patterns
• Zoom with the scroll wheel, pinch gesture, or the +/− buttons; drag to pan when zoomed in
• Tap or click any star, planet, or constellation name to see its details (magnitude, RA/Dec, where to look)

How It Works

1. Your date, time, and location determine the Local Sidereal Time
2. Each star's catalog position (Right Ascension and Declination) is converted to local Altitude and Azimuth coordinates
3. Objects above the horizon (altitude > 0°) are projected onto the circular chart using a stereographic projection
4. Planet positions are computed from orbital elements using Kepler's equation

Tips for Stargazing

• Use the Now button and Detect Location to see your current sky
• Allow 15-20 minutes for your eyes to adapt to the dark
• Use the Animate button to see how the sky changes over time
• Stars near the horizon appear dimmer due to atmospheric extinction
• The Milky Way is best viewed from a dark location with no light pollution

Coordinate Systems

• Right Ascension (RA) and Declination (Dec) define a star's fixed position on the celestial sphere (like longitude and latitude for the sky)
• Altitude (Alt) is the angle above the horizon (0° to 90°)
• Azimuth (Az) is the compass direction (0°=N, 90°=E, 180°=S, 270°=W)
• Local Sidereal Time (LST) indicates which part of the celestial sphere is currently overhead

You can embed this util on your own site as a widget. Adding ?embed=1 to the URL loads a compact version with just the tool itself; no header, menu, or documentation. Paste this snippet into your HTML:

Copy snippet Adjust the height to taste.