Light-Year, AU & Parsec Converter
Exact unit definitions and clearly labelled astronomical scale examples.
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- Free preview: the rules, dates and checks that apply to your figures, with every computed amount hidden.
- Locked until you unlock it: download and copy.
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About the Light-Year, AU & Parsec Converter
Convert distances among light-years, parsecs, kiloparsecs, astronomical units, light-time distance units, metres, kilometres and international miles. Vacuum light time and a chosen constant spacecraft speed provide two useful scale comparisons. Moon and Sun examples use the entered ephemeris instant; stellar and galactic presets are rounded source examples.
The free preview masks converted figures. A Pro pass opens every unit and time breakdown, copy and text or PDF reports. Exact unit definitions do not make an approximate preset distance an exact measurement.
How to use it
- Enter a nonnegative distance and unit, or select a calculated Moon/Sun or approximate stellar/galactic preset.
- Choose the headline unit and, for Moon or Sun, a UTC instant or now.
- Enter a positive constant spacecraft speed below light speed in m/s, km/s or percent of c.
- Calculate the preview; a pass opens the complete conversion and time tables, copy and report downloads.
Examples
1 light-year
9,460,730,472,580.8 km by definition; light time is one Julian year.
1 light-year at 10% of c
10 Julian years in the departure reference frame, before accounting for acceleration or braking.
Definitions and arithmetic
Distance conversions multiply by the defined metres per unit. Light time is distance/c, and cruise time is distance/speed. c is 299,792,458 m/s; a Julian year is 365.25 days; an au is 149,597,870,700 m; a parsec is (648,000/π) au. International miles use 1,609.344 m. Intermediate decimal precision is 50 digits; displayed values use up to 12 significant digits.
Sources
Limitations
- The Proxima, Galactic Centre and Andromeda examples are rounded published distances rather than current precision measurements.
- Constant-speed travel excludes acceleration, braking, gravity, cosmic expansion and traveller proper time. It is a scale calculation rather than a spacecraft trajectory.
- The parsec involves π, so numeric evaluation is finite precision even though the definition itself is exact. Extreme converted scales use exponent text rather than a silent binary overflow or underflow.
Privacy
On this device; its files download once
Calculation code and report fonts load from MySmartCoPilot on first use. Entered values stay on this device; the Moon and Sun presets are calculated locally without a third-party data request.
Frequently asked questions
What do I get without a pass?
Without a pass, Light-Year, AU & Parsec Converter shows the rules, dates and checks that apply to your figures, with every computed amount hidden. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
Is a light-year a time unit?
It is a distance: how far light travels in one Julian year in vacuum. The report separately shows the corresponding light-travel time.
Is the Sun always exactly one au away?
No. An au is an exact defined length. The Sun preset computes the changing Earth-centre to Sun-centre ephemeris distance.
Is cruise time the time felt by a traveller?
No. It is distance divided by speed in the departure reference frame, without acceleration or relativistic proper-time modelling.