Seasons and sky
Obliquity of the Ecliptic
Direct answer
Obliquity of the Ecliptic: The Obliquity of the Ecliptic is the angle between Earth's equatorial plane and its orbital plane, currently about 23.4 degrees.
Obliquity is the approximately 23.4-degree tilt between Earth equator and orbit.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Solar Declination, Axial Tilt, Astronomical Season, Equinox
Obliquity is the approximately 23.4-degree tilt between Earth equator and orbit.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Obliquity of the Ecliptic
Ancient astronomers estimated obliquity from solstitial solar altitudes; modern models track its slow variation.
Why Obliquity of the Ecliptic matters
Obliquity sets the maximum solar declination and is the primary geometric cause of terrestrial seasons.
Obliquity of the Ecliptic in practice: an example
The tropics lie near latitudes equal to the present obliquity because that is the limit of the overhead Sun.
Where readings of Obliquity of the Ecliptic go wrong
A common error is to treat 23.5 degrees as timelessly exact; obliquity changes slowly and depends on epoch.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: The Seasons and the Earth's Orbit - Official explanation of axial tilt, solstices, equinoxes, perihelion, aphelion, and seasonal sunlight.
- U.S. Naval Observatory Circular 179: The IAU Resolutions on Astronomical Reference Systems, Time Scales, and Earth Rotation Models - Technical reference for TAI, TT, TCG, TCB, TDB, UT1, sidereal time, epochs, and Earth rotation.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
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Common questions
What is the Obliquity of the Ecliptic?
The Obliquity of the Ecliptic is the angle between Earth's equatorial plane and its orbital plane, currently about 23.4 degrees.
What do people get wrong about the Obliquity of the Ecliptic?
A common error is to treat 23.5 degrees as timelessly exact; obliquity changes slowly and depends on epoch.
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