Sky science

Hour Angle

Direct answer

Hour Angle measures westward angular distance from the local meridian to an object’s hour circle.

It tells how far an object is from meridian transit.

Astronomy & SkywatchingThe Great Almanac DictionaryUpdated 2026-09-26

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At a glance

Found in: Astronomy & Skywatching
Related: Celestial Meridian, Local Meridian, Position Angle, Angular Separation

A refracting telescope on its mount, pointed at a field of stars — Observable sky · visual guide **Hour Angle**
It tells how far an object is from meridian transit.
A scientific orientation to scale, light, or motion; the article supplies the precise definition.

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The story behind Hour Angle

Hour angle was fundamental to transit instruments and equatorial mounts.

A one-minute story

The Wandering Stars

How the moving planets were watched, named and found, and what a transit is.

Why Hour Angle matters

Hour Angle links right ascension, local sidereal time, and telescope tracking.

Where readings of Hour Angle go wrong

Hour angle is angular time, not the duration an object has been visible.

Sources and editorial method

Research references used for this entry include:

U.S. Naval Observatory: Astronomical Almanac Glossary - Definitions for astronomical coordinates, time, reference systems, and observable phenomena.
International Astronomical Union: Standards of Fundamental Astronomy - IAU-maintained standards and algorithms for astronomical reference systems and coordinate transformations.

Source: The Great Almanac Dictionary
Category: Astronomy & Skywatching
Last updated: 2026-09-26

Calculate time from the meridian

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Celestial MeridianIt divides the local sky into eastern and western halves. Local MeridianIt is the observer-specific meridian of the sky. Position AngleIt gives a companion or feature’s direction around a reference point. Angular SeparationIt is the apparent distance between sky positions. AstronomyAstronomy is the science of celestial objects, space, and the physical universe. SkywatchingSkywatching is direct observation of the changing day and night sky.

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