Convert Astronomical Distances

Calculator for parsec, light year, light second, astronomical units, kilometers and miles. A parsec, or parallax second, is equal to 3.26 light-years. The astronomical unit is the average distance from the earth to the sun, which is almost 150 million kilometers.

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Example: the closest star to us after the sun is Alpha Centauri with a distance of 4.34 light years. This corresponds to 274466.27 astronomical units.

Since the speed of light in a vacuum is constant, 299792.458 kilometers per second, a precise distance can be calculated using this speed and a given duration. A light-second, for instance, is the distance light travels in one second, 299792.458 kilometers. Similarly, a light-minute is sixty times the distance of a light-second, and a light-hour is sixty times that of a light-minute. The light-year also describes a distance, a vast one, amounting to approximately nine and a half trillion kilometers. The Moon is just over one light-second away from us, while the Sun is slightly more than eight light-minutes away. The distance to Saturn exceeds one light-hour. Depending on the definition used, the solar system, extending to the hypothesized Oort cloud, spans roughly 1.5 light-years, with the density of matter decreasing when moving outward.
Looking into the distance is always looking into the past. When we observe the Moon, that past is only a second old. With stars, however, it spans years. The most distant stars visible to the naked eye are thousands of light-years away. Deneb, which appears very bright, is about 1,500 light-years away. Currently, the leading candidate is the very faint star V509 Cassiopeiae, located 13,000 light-years away.

The speed of light is the maximum speed at which any effect can propagate in the universe. Nothing travels faster than light, matter always moves more slowly. The speed of light is an absolute value, a fundamental constant of nature, whereas space and time are relative. This concept is described by Einstein's special theory of relativity.

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Last updated on 08/13/2026. Author: Jürgen Kummer

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