gnomon
Sundial's pointing blade
A gnomon is the part of a sundial that casts the shadow—typically an upright rod or triangular blade.
The shadow's position against marked hours tells the time.
In geometry, a gnomon is the L-shaped figure remaining when a smaller parallelogram is removed from a larger similar one.
Graduated circular indicator
- shadowLight blocked by object
- hourSixty-minute span
- noonDay's exact middle
- meridianPole-to-pole great circle
solar · calibrate · hemicycle · equatorial · horizontal · vertical · portable · pillar
Sun crosses celestial midline
- solsticeDay of maximum tilt
- celestialOf the sky above
- eclipticSun's apparent annual path
- zenithPoint straight overhead
nadir · declination · azimuth · transit · horizon · latitude · longitude · astronomical
Something that extends outward
- perpendicularAt right angles
- angleGeometric measure of rotation
- vertexPoint where edges converge
- parallelogramQuadrilateral with paired parallels
similar · ratio · proportion · theorem · plane · intersection · remainder · L-shape
Timekeeping science and craft
Ancient Mesopotamian capital
- EgyptNortheastern African nation
- AlexandriaEgyptian Mediterranean port
- HellenisticOf post-Alexander Greek civilization
- PtolemyGreco-Egyptian astronomer, geographer
Herodotus · Pliny · antiquity · ziggurat · pyramid · Stonehenge · Thales · philosopher
dial
Graduated circular indicator
meridian · solar · calibrate · hemicycle · equatorial · horizontal · vertical · portable · pillar · obelisk
equinox
Sun crosses celestial midline
zenith · nadir · declination · azimuth · transit · horizon · latitude · longitude · astronomical · meridian
projection
Something that extends outward
- perpendicularAt right angles
- angleGeometric measure of rotation
- vertexPoint where edges converge
parallelogram · similar · ratio · proportion · theorem · plane · intersection · remainder · L-shape · carpenter's square
horology
Timekeeping science and craft
Babylon
Ancient Mesopotamian capital
- EgyptNortheastern African nation
- AlexandriaEgyptian Mediterranean port
- HellenisticOf post-Alexander Greek civilization
Ptolemy · Herodotus · Pliny · antiquity · ziggurat · pyramid · Stonehenge · Thales · philosopher · astronomer
- timekeepingclock, watch, watches, clocks, timer
- ancient timekeepingsundials, water clocks, hourglasses, sand clocks, solar time
- antique instrumentsastrolabe, sextant, octant, quadrant, theodolite
- Chinese astronomyarmillary sphere, celestial globe, star charts, star maps, lunar calendar
- Greek inventionsArchimedes screw, astrolabe, automata, ballista, catapult
- ancient clockssundial, water clock, hourglass, obelisk, sandglass