Convert between light years, parsecs, astronomical units, and kilometers for cosmic distances.
Light Year Distance Calculator expresses one cosmic distance in light years, parsecs, astronomical units, and kilometers. Supply a numeric distance in any supported unit to see equivalent representations at interstellar, Solar System, and terrestrial scales. The most common mistake is treating a light-year as elapsed time. It is a unit of length. Converting a distance to light years does not determine a spacecraft's journey time, although the unit is based on how far light travels in vacuum during a Julian year.
Each supported unit describes length on a different scale. A light-year is tied to light's vacuum speed over a Julian year. An astronomical unit is a defined fixed length. A parsec is associated with the distance at which one astronomical unit subtends one arcsecond. Kilometers express the same distance using an SI unit.
The entered number and its source unit establish one physical distance. Fixed relationships between the four units then give the corresponding numerical values. A parsec entry therefore represents exactly the same span when expressed in light years, astronomical units, or kilometers. This operation changes units, not the location, uncertainty, or measured accuracy of an astronomical object.
No, not for a spacecraft or other object moving below the speed of light. A light-year is the distance light travels in vacuum during one Julian year. The numerical distance in light years can describe ideal vacuum light-travel time in Julian years, but an actual journey also depends on speed, acceleration, route, and other physical conditions.
No. Redshift is dimensionless, and converting it to distance requires a cosmological model and selected parameters. This calculator begins with a distance already expressed in light years, parsecs, astronomical units, or kilometers. It only changes that distance's unit, so it cannot derive distance from redshift, brightness, parallax observations, or an object's name.
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