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Calculation & Conversion Tools

Five fast calculators and converters for the numbers astronomers use every day — from Julian dates and cosmic distances to planetary weights and orbital periods.

All Tools Observation Calculation & Conversion Physics
Calculation

Planet Weight

Weight on other planets.

 Calculation

Julian Date

Astronomical date converter.

 Calculation

Distance Converter

LY, AU, KM conversions.

 Calculation

Orbital Period

Kepler's 3rd Law.

 Calculation

Planet Density

Rocky vs Gas composition.

Everyday Numbers, Done Right

Astronomy runs on conversion tables: calendar dates become Julian Dates, kilometers become astronomical units and light-years, and a world's mass and radius reveal whether it is rocky like Earth or gassy like Jupiter. These calculators handle those everyday transformations instantly, using the same constants published by NASA and the IAU.

Every result is paired with the exact formula behind it, so a quick lookup can become a quick lesson. For observing-session planning, see the observation tools; for deeper astrophysics, try the physics tools, or view all 20 tools.