RA/Dec to Alt/Az Coordinate Converter
Enter a star or object's catalog coordinates, your location, and the date and time to get its current altitude, azimuth, and rise/transit/set times. Nothing uploaded.
Sky position
Learn more: Astronomical coordinate conversion
When you need this: manual telescopes and planning observations
GoTo telescopes handle the conversion internally. But Dobsonian telescopes, equatorial mounts being star-aligned, or any manual finder scope requires you to know the horizontal coordinates for your location and time. The catalog gives you RA/Dec; you need Alt/Az to actually move the scope.
Altitude and azimuth in three steps
Enter the RA and Dec from a star catalog in hours/minutes/seconds and degrees/arcminutes/arcseconds format. Enter your observer location as latitude and longitude in decimal degrees, plus the date and time in UTC. The converter then calculates the altitude (degrees above the horizon), azimuth (compass bearing), and rise/transit/set times for that location and moment.
FAQ
What is the difference between RA/Dec and Alt/Az coordinates?
Right Ascension (RA) and Declination (Dec) are catalog coordinates fixed to the celestial sphere - they don't change with time or observer location (ignoring proper motion and precession). Altitude (height above horizon) and Azimuth (compass bearing) describe where an object actually is in the sky at a specific time and place. You need the conversion to point a manual telescope.
How do I find a star's coordinates for telescope pointing?
Look up the star's RA and Dec in a catalog (Stellarium, Sky Safari, Wikipedia). Enter these coordinates plus your latitude, longitude, and current date/time into the converter. The resulting altitude and azimuth tell you where to point your telescope - altitude is degrees above the horizon, azimuth is the compass bearing.
Does the converter account for atmospheric refraction?
The converter uses the standard astronomical calculation without refraction correction. Refraction becomes significant below about 5 degrees altitude where the atmosphere bends the apparent position of objects. For objects well above the horizon (which is where most visual observations occur) the refraction correction is under 1 arcminute.