Astronomical tables

Astronomical tables are organized numerical values used to calculate or predict celestial bodies’ positions and motions at specified times. They encode observations or models so that astronomical calculations can be performed without repeating them from first principles.

Ephemeris: A tabulation or record of the predicted positions of celestial bodies at specified times. Ephemerides are the direct output that many astronomical tables are designed to provide.
Babylonian astronomy: The systematic observation and mathematical study of celestial phenomena in ancient Babylonia. Babylonian scholars developed early numerical procedures and records for predicting celestial events.
Nautical almanac: An annual reference giving astronomical data for navigation and related calculations. Its tabulated coordinates and timing data let navigators determine position at sea.
Orrery: A mechanical model that represents the motions and relative positions of celestial bodies. An orrery displays motion physically, while tables encode positions numerically.
Longitude: An angular coordinate measuring position east or west of a reference meridian. Reliable lunar and planetary tables helped make longitude estimable from celestial observations.
Interpolation: A method for estimating a value between known data points. Interpolation supplies positions for dates that fall between the table’s listed entries.
Almagest: Claudius Ptolemy’s second-century astronomical treatise presenting a mathematical model of the heavens. Its tables made Ptolemy’s planetary and lunar calculations usable in practice.
Lunar distance method: A method of finding longitude by measuring the Moon’s angular distance from another celestial body. Navigators compared observed lunar distances with predicted values in astronomical tables.
Astrolabe: An instrument that represents the celestial sphere and supports astronomical measurement and calculation. Unlike a table’s stored values, an astrolabe performs calculations through a physical model.
Universal Time: A time standard based on Earth's rotation, formalized for global astronomical and civil use. Astronomical predictions required consistent time references to compare calculated and observed positions.

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