📐RA/Dec to Alt/Az Converter
Convert equatorial coordinates (Right Ascension, Declination) to local horizontal coordinates (Altitude, Azimuth) for any time and location.
Convert RA/Dec to Altitude/Azimuth for any location and time. Includes presets for famous stars and deep-sky objects. Free.
How to Use RA/Dec to Alt/Az Converter — Step by Step
- 1Select a preset object (Sirius, Betelgeuse, Polaris, M31, etc.) or enter custom RA/Dec
- 2Enter your latitude and longitude (or click 'Use my location')
- 3Set the date and UTC time of observation
- 4Click 'Convert Coordinates'
- 5View altitude, azimuth, hour angle, and viewing quality
Why Use ToolNest for RA/Dec to Alt/Az Converter?
- 📐Full equatorial to horizontal coordinate transformation using LST
- ⭐7 preset objects: Sirius, Betelgeuse, Polaris, M31, M42, Pleiades, Vega
- 📍Browser geolocation for automatic observer position
- 🧭Cardinal direction output (N, NNE, NE, etc.) for physical sky navigation
- ✅Shows whether object is above or below horizon with viewing quality
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Frequently Asked Questions
What are RA and Dec?
Right Ascension (RA) and Declination (Dec) are equatorial coordinates that describe a fixed point on the celestial sphere, independent of observer location or time. RA is measured in hours (0–24h), Dec in degrees (-90° to +90°).
What are Altitude and Azimuth?
Altitude is the angle above the horizon (0° = horizon, 90° = zenith). Azimuth is the compass bearing from north (0°/360° = north, 90° = east, 180° = south, 270° = west). Together they define where to look in the local sky.
Why does the Alt/Az change over time?
RA/Dec are fixed (sidereal coordinates), but the sky rotates due to Earth's rotation. The same star rises in the east, crosses the meridian (highest altitude), and sets in the west — its Alt/Az changes constantly.
What is an hour angle?
Hour angle is the time since an object crossed the meridian (or time until, if negative). It's measured in hours: 0h = on the meridian (highest altitude), +6h = 6 hours west of meridian. HA = LST - RA.