What is the difference between altitude and azimuth?

Altitude (or elevation) is the angle of an object above the horizon, ranging from 0° (horizon) to 90° (zenith). Azimuth is the compass bearing measured clockwise from due North (0°/360°), so East = 90°, South = 180°, West = 270°.

What are right ascension and declination?

Right ascension (RA) and declination (Dec) are the equatorial coordinates fixed to the celestial sphere, analogous to longitude and latitude on Earth. RA is measured in hours (0h–24h) eastward; Dec is measured in degrees (−90° to +90°) from the celestial equator.

Why do I need to enter a date and time?

The horizontal coordinates of a star change continuously as Earth rotates. The calculation first derives the Local Sidereal Time (LST) from your date, time, and longitude, then computes the Hour Angle (LST − RA), which determines where the object sits in your local sky.

What time zone should I use?

All calculations are performed in UTC (Universal Time). Convert your local time to UTC before entering it, or enable the "Use my current UTC time" toggle to prefill the fields automatically.

How accurate is this calculator?

The tool uses the standard spherical-trigonometry formula with a simplified Julian Date / Greenwich Sidereal Time calculation. Accuracy is within a few arcminutes, sufficient for visual observation planning. For sub-arcsecond precision (e.g. astrometry), use dedicated software such as Stellarium or ERFA.

What does a negative altitude mean?

A negative altitude means the object is below the horizon and therefore not visible from your location at that time. Try a different date/time or wait until the Earth rotates so the object rises above the horizon.

Altitude Azimuth Calculator

Name: Altitude Azimuth Calculator
Availability: InStock
Author: Nham Vu

Convert right ascension and declination to altitude and azimuth for any observer location and time.

Input Coordinates & Observer

Right Ascension (RA)

hours

min

sec

Declination (Dec)

deg

arcmin

arcsec

Observer Latitude (°)

Positive = North, Negative = South

Observer Longitude (°)

Positive = East, Negative = West

Date & Time (UTC)

Quick Examples

Fill in coordinates and observer location, then click Calculate.

Summary

Convert right ascension and declination to altitude and azimuth for any observer location and time.

How it works

Enter the right ascension (RA) in hours, minutes, and seconds.
Enter the declination (Dec) in degrees, arcminutes, and arcseconds.
Provide the observer's geographic latitude and longitude in decimal degrees.
Select or type the date and time (UTC) of observation.
Click Calculate — the tool computes Local Sidereal Time, Hour Angle, altitude, and azimuth.
Use the azimuth compass rose to visually confirm the direction.

Use cases

Point a telescope at a star given its catalog RA/Dec coordinates.
Determine whether a celestial object is above the horizon at observation time.
Plan a night sky session by checking object visibility windows.
Verify planetarium software outputs against hand calculations.
Track the position of planets, the Moon, or the Sun for a specific time.
Educational demonstration of coordinate system transformations in astronomy.
Astrophotography planning — find the altitude to estimate atmospheric extinction.
Satellite ground-track analysis for amateur radio operators.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu