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Sidereal Time

Sidereal time is an astronomical way of keeping time by Earth's rotation relative to the stars rather than the Sun.

International Atomic Time

International Atomic Time, or TAI, is the continuous atomic time scale that underpins UTC, scientific timing, navigation, and modern time standards.

Leap Second

A leap second is a one-second adjustment to Coordinated Universal Time, used to keep civil time close to Earth's uneven rotation.

Coordinated Universal Time

Coordinated Universal Time, or UTC, is the international reference time scale used to synchronize civil time, networks, navigation, science, and time zones around the world.

Society

Daylight Saving Time

Daylight saving time is the seasonal practice of setting clocks forward, usually by one hour, so daylight falls later in the evening during part of the year.

Time Zone

A time zone is a region that uses the same civil time, usually defined as an offset from Coordinated Universal Time and shaped by geography, law, and local practice.

International Date Line

The International Date Line is the mostly Pacific boundary where neighboring places can be on different calendar dates.

Prime Meridian

The Prime Meridian is the reference line for 0 degrees longitude, used to measure east-west position and connect geography with global timekeeping.

Equator

The Equator is the imaginary circle around Earth's middle that marks 0 degrees latitude and separates the Northern and Southern hemispheres.

Latitude and Longitude

Latitude and longitude are the angular coordinates used to describe positions on Earth, giving every place a north-south and east-west address.

Map Projection

A map projection is a mathematical way to show the curved surface of Earth on a flat map, screen, or coordinate grid while managing unavoidable distortion.

Technology

Geographic Information System

A geographic information system, or GIS, is a system for storing, analyzing, managing, and visualizing information connected to locations.

Remote Sensing

Remote sensing is the science of collecting information about objects or places from a distance, usually with sensors on satellites, aircraft, drones, or ground platforms.

Geodesy

Geodesy is the science of measuring and representing Earth's shape, gravity field, orientation, and positions so maps, GPS, surveys, and height systems line up.

Technology

GPS

GPS is the U.S. satellite navigation system that provides positioning, navigation, and timing signals to receivers around the world.

Atomic Clock

An atomic clock is a precision timekeeper that uses the stable frequency of atomic transitions to define and maintain modern time standards.

Technology

Marine Chronometer

A marine chronometer is a precise timekeeper made for ships, allowing navigators to compare local time with a reference meridian and calculate longitude at sea.

Lodestone

Lodestone is naturally magnetized magnetite, a mineral that can attract iron and helped people turn magnetism into practical direction-finding.

Magnetic Compass

A magnetic compass is a direction-finding instrument whose magnetized needle aligns with Earth's magnetic field, helping travelers, sailors, pilots, and surveyors find bearings.

Sextant

A sextant is a precision instrument that measures angles between visible objects, especially a celestial body and the horizon, so navigators can estimate position at sea.

Codex

A codex is a book form made from leaves bound along one edge, a format that gradually replaced many scrolls and shaped how readers navigate, store, and preserve texts.

Parchment

Parchment is a writing material made from prepared animal skin, central to medieval manuscripts, codices, legal documents, maps, bindings, and illuminated books.

Papyrus

Papyrus was both a Nile wetland plant and the ancient writing material made from its pith, used for scrolls, letters, accounts, literature, and sacred texts.