Dictionary category
Seasons & Earth Almanac
Earth-Sun seasons, daylight and twilight, atmospheric light, lunar rhythms, tides, and recurring terrestrial phenomena.
Direct answer
Earth-Sun seasons, daylight and twilight, atmospheric light, lunar rhythms, tides, and recurring terrestrial phenomena. This category gathers sourced definitions, concrete examples, observing or calculation cautions, and connected reference terms in one place.
What this category covers
Seasons & Earth Almanac pages begin with the measured or historical definition, then explain why the term matters, how it is used, a concrete example, relevant limits, and the sources behind the entry. Scientific observation, historical practice, cultural star lore, and symbolic interpretation remain explicitly separated.
How to use this dictionary category
Use this category as a reference layer beside the live Almanac guides. Start with the definition, follow the sibling terms that explain the same process or instrument, then open the relevant sky, season, constellation, ephemeris, or historical guide for a wider view.
Seasons & Earth Almanac terms
22-Degree HaloA 22-Degree Halo is the common ice-crystal ring around the Sun or Moon.
AlpenglowAlpenglow is warm twilight illumination on elevated terrain.
Amphidromic PointAn Amphidromic Point is a nodal center of a rotating tidal system.
Anticrepuscular RaysAnticrepuscular Rays are perspective-converging beams opposite the Sun.
Astronomical DawnAstronomical Dawn begins astronomical twilight at a -18-degree solar altitude.
Astronomical DuskAstronomical Dusk ends astronomical twilight at a -18-degree solar altitude.
Astronomical SeasonAn Astronomical Season runs from one equinox or solstice to the next.
Axial TiltEarth Axial Tilt is the lean of its rotation axis relative to its orbit.
Belt of VenusThe Belt of Venus is the rosy antisolar band above Earth shadow.
Blue HourBlue Hour is the cool-toned twilight interval favored by photographers.
Brocken SpectreA Brocken Spectre is a magnified-looking shadow projected onto mist.
Circumzenithal ArcA Circumzenithal Arc is an upside-down rainbow-like halo high in the sky.
Civil DawnCivil Dawn begins morning civil twilight at a -6-degree solar altitude.
Civil DuskCivil Dusk ends evening civil twilight at a -6-degree solar altitude.
Civil TwilightCivil Twilight spans Sun altitudes from 0 to -6 degrees.
Climatological NormalA Climatological Normal is a period-based reference for typical climate conditions.
Cooling Degree DayCooling Degree Days estimate warm-weather cooling demand above a base temperature.
Crepuscular RaysCrepuscular Rays are sunward light-and-shadow beams shaped by perspective.
DawnDawn is the brightening twilight before sunrise.
Day LengthDay Length is the elapsed time from local sunrise to local sunset.
December SolsticeThe December Solstice is the Sun annual southern declination extreme.
Diurnal TideA Diurnal Tide has one principal high and one principal low each lunar day.
DuskDusk is the fading twilight after sunset.
Earth ShadowThe Earth Shadow is the twilight dark band on the antisolar horizon.
Earth-Sun Distance CycleThe Earth-Sun Distance Cycle is the yearly change between Earth closest and farthest solar distances.
EquiluxEquilux is the locally dependent date of roughly equal daylight and darkness.
Equinoctial TideAn Equinoctial Tide is a seasonally described spring tide near an equinox.
EquinoxAn Equinox occurs when the Sun crosses the celestial equator.
Frost DateA Frost Date estimates seasonal freeze timing from local climate records.
GloryA Glory is an antisolar ring pattern formed in cloud or fog droplets.
Golden HourGolden Hour is the warm low-Sun interval used in photography and observation.
Green FlashA Green Flash is a fleeting green solar-edge effect near a clear horizon.
Growing Degree DayGrowing Degree Days accumulate temperature above a crop or organism base.
Heating Degree DayHeating Degree Days estimate cold-weather heating demand below a base temperature.
Horizon RefractionHorizon Refraction raises and distorts low celestial objects.
Inferior MirageAn Inferior Mirage is the apparent image below an object over strongly heated ground or water.
June SolsticeThe June Solstice is the Sun annual northern declination extreme.
March EquinoxThe March Equinox is the Sun's northward crossing of the celestial equator.
Meteorological SeasonA Meteorological Season is a three-month climatological grouping.
Midnight SunThe Midnight Sun is sunlight visible around local midnight in polar summer.
Mixed TideA Mixed Tide has unequal successive high and low waters.
MoonriseMoonrise is the local horizon time when the Moon begins to appear.
MoonsetMoonset is the local horizon time when the Moon finishes setting.
Nautical DawnNautical Dawn begins nautical twilight at a -12-degree solar altitude.
Nautical DuskNautical Dusk ends nautical twilight at a -12-degree solar altitude.
Nautical TwilightNautical Twilight spans Sun altitudes from -6 to -12 degrees.
Neap TideA Neap Tide has a smaller tidal range near quarter-Moon geometry.
Obliquity of the EclipticObliquity is the approximately 23.4-degree tilt between Earth equator and orbit.
Perigean Spring TideA Perigean Spring Tide combines syzygy with a relatively close Moon.
PhenologyPhenology tracks seasonal events such as flowering, migration, and leaf change.
PhotoperiodPhotoperiod is the daily duration of light experienced by an organism or place.
Polar DayPolar Day is continuous daylight lasting a full day or longer.
Polar NightPolar Night is a full day or longer without sunrise.
Season Length AsymmetrySeason Length Asymmetry is the unequal time between successive equinoxes and solstices.
Seasonal LagSeasonal Lag is the delay between peak solar forcing and peak seasonal response.
Semidiurnal TideA Semidiurnal Tide has two broadly similar highs and lows each lunar day.
September EquinoxThe September Equinox is the Sun's southward crossing of the celestial equator.
Slack WaterSlack Water is the low-current interval between flood and ebb flow.
Solar DeclinationSolar Declination is the Sun celestial latitude relative to the equator.
Solar InsolationSolar Insolation measures incoming sunlight energy on a surface.
Solar TerminatorThe Solar Terminator is the day-night boundary across Earth.
SolsticeA Solstice marks the Sun's greatest apparent northward or southward position.
Spring TideA Spring Tide has a larger tidal range near new and full Moon alignments.
Subsolar PointThe Subsolar Point is the location receiving vertical noon sunlight.
Sun PillarA Sun Pillar is a vertical low-Sun reflection from plate-like ice crystals.
SundogA Sundog is a colored ice-crystal light patch beside the Sun.
SunriseSunrise is the calculated first appearance of the Sun's upper edge at the horizon.
SunsetSunset is the calculated disappearance of the Sun's upper edge below the horizon.
Tidal BoreA Tidal Bore is an incoming tidal wave advancing upriver.
Tidal DatumA Tidal Datum is a local water-level reference based on tide observations.
Tidal RangeTidal Range is the height difference from high water to low water.
TideA Tide is the recurring rise and fall of ocean level shaped mainly by lunar and solar gravity.
Continue learning
Continue into the live sky, space weather, universal timing, and the wider field surrounding the current season.
Open Worldwide WatchCommon questions
What is in the Seasons & Earth Almanac dictionary?
Earth-Sun seasons, daylight and twilight, atmospheric light, lunar rhythms, tides, and recurring terrestrial phenomena.
How should I use this category?
Use it to understand a term, compare neighboring concepts, check sources and cautions, and continue into the relevant live or long-form Almanac guide.
How do these entries connect to the live Almanac?
The dictionary defines the reference language. The Almanac guides add current sky data, larger explanations, and practical observing or historical context.
