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Interactive astronomical calculations and educational tools.
Explore the cosmos with precision algorithms based on Jean Meeus' methods.

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Explore the Cosmos

Choose a calculator to begin your astronomical journey

Sunrise, sunset, twilight times, solar position and equation of time

Lunar phases, position, eclipses, and surface features

Planetary positions, magnitudes, Jupiter's moons, Saturn's rings

Messier catalog, bright stars, double stars, and constellations

Telescope calculator, magnification, field of view, limiting magnitude

Meteor showers, eclipses, planetary conjunctions and elongations

Compute comet positions from orbital elements

Plan observing sessions — what's up tonight? Best objects for the month

AstroCalc implements classical computational astronomy algorithms from authoritative sources:

Jean Meeus — "Astronomical Algorithms" and "Astronomical Formulae for Calculators"
USNO — U.S. Naval Observatory Almanac algorithms
Lieske (1979) — Precession of the equinoxes
VSOP87 — Planetary position theory

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