solar time
Sun-based timekeeping
Solar time is time measured by the sun's position in the sky rather than by clocks.
When the sun reaches its highest point, that's solar noon—which rarely matches 12:00 on your watch because time zones average solar time across wide regions.
The sundial shows solar time, not standard time.
Astronomers and navigators distinguish apparent solar time (actual sun position) from mean solar time (averaged to account for Earth's elliptical orbit).
Shadow-based timekeeper
- gnomonSundial's shadow-casting projection
- horologyTimekeeping science and craft
- shadowLight blocked by object
- timepieceHour-measuring device
calibration · obelisk · water clock · hemicycle · Vitruvius
Pole-to-pole great circle
- zenithPoint straight overhead
- eclipticSun's apparent annual path
- equinoxSun crosses celestial midline
- celestialOf the sky above
ephemeris · transit · declination · hour angle · celestial equator · Ptolemy · armillary sphere
London district, meridian origin
- prime meridianZero-degree longitude line
- GMTGlobal time baseline
- UTCUniversal time standard
- longitudeEast-west angular distance
Morning light's arrival
- sunsetDay yielding to darkness
- dawnDay's first glow
- duskDimming after sundown
- twilightLight after sunset
morning · afternoon · golden hour · daybreak · daytime · sunshine · sunlight · photoperiod
Daily biological cycle
- diurnalActive during daylight
- nocturnalActive during darkness
- chronobiologyStudy of living timing patterns
- biological clockInnate cycle regulator
entrainment · melatonin · sleep-wake cycle · seasonal rhythm · sun exposure · sungazing · heliotropism
sundial
Shadow-based timekeeper
- gnomonSundial's shadow-casting projection
- horologyTimekeeping science and craft
- shadowLight blocked by object
timepiece · calibration · obelisk · water clock · hemicycle · Vitruvius
meridian
Pole-to-pole great circle
celestial · ephemeris · transit · declination · hour angle · celestial equator · Ptolemy · armillary sphere
Greenwich
London district, meridian origin
- prime meridianZero-degree longitude line
- GMTGlobal time baseline
- UTCUniversal time standard
longitude · chronometer · earth rotation · International Date Line
sunrise
Morning light's arrival
twilight · morning · afternoon · golden hour · daybreak · daytime · sunshine · sunlight · photoperiod · azimuth
circadian
Daily biological cycle
- diurnalActive during daylight
- nocturnalActive during darkness
- chronobiologyStudy of living timing patterns
biological clock · entrainment · melatonin · sleep-wake cycle · seasonal rhythm · sun exposure · sungazing · heliotropism
- ancient timekeepingsundials, water clocks, gnomon, hourglasses, sand clocks
- timekeepingclock, watch, watches, clocks, timer
- sky and timesun, moon, stars, planets, comet
- astronomical clocksstar wheel, orrery, celestial sphere, lunar calendar
- celestial navigationcelestial navigation, sextant, astrolabe, nautical almanac, celestial sphere
- astronomystars, moon, sun, planet, planets