hour angle: meaning, definition, pronunciation and examples
Very Low (Technical/Specialized)Technical / Scientific
Quick answer
What does “hour angle” mean?
The angular distance between the meridian of a celestial body and the hour circle of a given point (usually the First Point of Aries), measured westward along the celestial equator, expressed in hours, minutes, and seconds.
Audio
Pronunciation
Definition
Meaning and Definition
The angular distance between the meridian of a celestial body and the hour circle of a given point (usually the First Point of Aries), measured westward along the celestial equator, expressed in hours, minutes, and seconds.
In navigation and astronomy, it is a coordinate that, along with declination, specifies the position of a point on the celestial sphere in the equatorial coordinate system. Conceptually, it represents how far (in time) a celestial body is west of the local meridian.
Dialectal Variation
British vs American Usage
Differences
No significant differences in meaning or usage. Spelling conventions follow general UK/US patterns (e.g., 'centre' vs. 'center' in related texts).
Connotations
Purely technical, without cultural connotations.
Frequency
Equally rare in both dialects, confined to specialized fields.
Grammar
How to Use “hour angle” in a Sentence
[calculate/find/determine] the hour angle of [celestial body][express/measure] the hour angle in [hours/minutes/seconds][convert] the hour angle to [degrees]Vocabulary
Collocations
Examples
Examples of “hour angle” in a Sentence
adjective
British English
- The hour-angle measurement is critical for the telescope's alignment.
- Consult the hour-angle tables in the nautical almanac.
American English
- The hour-angle coordinate system is fundamental to celestial navigation.
- We need the hour-angle data from the ephemeris.
Usage
Meaning in Context
Business
Not used.
Academic
Used in astronomy, astrophysics, and geomatics courses and papers.
Everyday
Not used.
Technical
Core term in celestial navigation, ephemeris data, telescope pointing, and satellite tracking.
Vocabulary
Synonyms of “hour angle”
Strong
Neutral
Weak
Watch out
Common Mistakes When Using “hour angle”
- Pronouncing 'hour' without the silent 'h' (e.g., 'our angle').
- Confusing it with 'right ascension' (another celestial coordinate).
- Forgetting it is measured westward.
FAQ
Frequently Asked Questions
No. Right Ascension (RA) is a fixed celestial longitude measured eastward from the First Point of Aries. Hour Angle is the angular distance *westward* from the observer's local meridian to the object's hour circle, so it changes with time and the observer's location.
Because it is conventionally expressed in units of time (hours, minutes, seconds), where 1 hour equals 15 degrees of arc (360 degrees / 24 hours = 15 degrees/hour).
Primarily in textbooks and practice for celestial navigation (using a sextant), astronomy observing guides, satellite tracking documentation, and geodesy.
LHA = Greenwich Hour Angle (GHA) of the body + Observer's Longitude (East positive, West negative). The result is usually reduced to a value between 0° and 360°.
The angular distance between the meridian of a celestial body and the hour circle of a given point (usually the First Point of Aries), measured westward along the celestial equator, expressed in hours, minutes, and seconds.
Hour angle is usually technical / scientific in register.
Hour angle: in British English it is pronounced /ˈaʊər ˌæŋɡl/, and in American English it is pronounced /ˈaʊr ˌæŋɡəl/. Tap the audio buttons above to hear it.
Learning
Memory Aids
Mnemonic
Think of the sky as a giant 24-hour clock. The 'hour angle' tells you how many 'hours' a star has moved from its noon position overhead.
Conceptual Metaphor
THE CELESTIAL SPHERE IS A CLOCK FACE; TIME IS ANGULAR DISTANCE.
Practice
Quiz
What does the 'hour angle' of a celestial body specifically measure?