Hour Angle

Definition

Hour angle is an astronomical coordinate measuring how far a celestial body lies west of the local meridian, along the celestial equator. It may be expressed in degrees or hours, with one hour equal to 15 degrees. A body on the meridian has an hour angle of zero. The value increases as Earth rotates and can be calculated from local sidereal time and the body’s right ascension.

Astrological Meaning

In astrology, hour angle is primarily a technical factor used in establishing the sky’s orientation for a particular time and place. It helps connect celestial coordinates with the local horizon and meridian, supporting accurate calculation of angles, house cusps, and planetary positions relative to the chart. It does not usually carry a separate symbolic interpretation like a planet, sign, or aspect. Hour angle should not be confused with planetary hours, which belong to a traditional system of assigning planetary rulers to portions of the day and night.

Why It Matters

Hour angle matters because astrology depends on precise timing and location. Small differences in local time or longitude can alter the relationship between a celestial body and the meridian, potentially affecting the Ascendant, Midheaven, houses, and angularity. Understanding the term is especially helpful when studying traditional chart calculation, astronomical tables, or astrology software. It also clarifies how apparent daily motion arises from Earth’s rotation rather than from rapid movement of the planets themselves.

Related Encyclopedia Entries

• Traditional Astrology
• Astrological Terminology
• Natal Chart