Sky science
Astronomical Nadir
Direct answer
Astronomical Nadir: The Astronomical Nadir is the point on the celestial sphere directly below an observer, opposite the zenith.
It is the lower endpoint of the local vertical.
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At a glance
- Found in
- Astronomy & Skywatching
- Related
- South Celestial Pole, Zenith, Prime Vertical, Great Circle
It is the lower endpoint of the local vertical.
A scientific orientation to scale, light, or motion; the article supplies the precise definition.
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The story behind Astronomical Nadir
Zenith-nadir axes were embodied in plumb-based observational instruments.
A one-minute story
The Wandering Stars
How the moving planets were watched, named and found, and what a transit is.
Why Astronomical Nadir matters
Astronomical Nadir completes horizon geometry and distinguishes astronomy from the astrological chart angle called Nadir.
Astronomical Nadir in practice: an example
A great circle through zenith and nadir defines a vertical circle.
Where readings of Astronomical Nadir go wrong
The astronomical nadir is normally blocked by Earth and is not an observing target.
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
Complete the local vertical axis
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Common questions
What is the Astronomical Nadir?
The Astronomical Nadir is the point on the celestial sphere directly below an observer, opposite the zenith.
What do people get wrong about the Astronomical Nadir?
The astronomical nadir is normally blocked by Earth and is not an observing target.
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