Seasons and sky
Moonset
Direct answer
Moonset is the calculated instant when the Moon's upper limb disappears below the observer's horizon under standard rise-and-set assumptions.
Moonset is the local horizon time when the Moon finishes setting.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Astronomical Season, Meteorological Season, Equinox, Solstice
Moonset is the local horizon time when the Moon finishes setting.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Moonset
Moonset tables became a routine part of astronomical and navigational almanacs because the event depends on lunar motion and observer location.
Why Moonset matters
Moonset determines dark-sky windows and explains whether Moon light will interfere with evening or predawn observing.
Moonset in practice: an example
Observers may wait until after a bright Moon sets to see fainter meteors or the Milky Way.
Where readings of Moonset go wrong
A common error is to treat a geometric set time as exact for an obstructed horizon.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Rise, Set, and Twilight Definitions - Definitions used by USNO for sunrise, sunset, moonrise, moonset, and twilight.
- U.S. Naval Observatory: Complete Sun and Moon Data - Authoritative astronomical data services for positions, phases, and rise and set events.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
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More in Seasons & Earth Almanac
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Common questions
What is Moonset?
Moonset is the calculated instant when the Moon's upper limb disappears below the observer's horizon under standard rise-and-set assumptions.
What do people get wrong about Moonset?
A common error is to treat a geometric set time as exact for an obstructed horizon.
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