Astronomical Unit Calculator
Convert any number of astronomical units to kilometers, miles, light-minutes, light-seconds, light-years, and parsecs. Essential for astronomy, space science, and education.
1 AU = average Earth-Sun distance
What is an astronomical unit (AU)?
An astronomical unit (AU) is the average distance from Earth to the Sun, approximately 92.96 million miles or 149.6 million kilometers. It is defined by the International Astronomical Union as exactly 149,597,870.7 kilometers. AU is the fundamental unit for measuring distances within our solar system, providing a convenient scale for planetary orbits.
How far is 1 AU in miles and kilometers?
1 AU = approximately 92,955,807 miles or 149,597,871 kilometers. Light travels this distance in about 8.3 minutes (light-minutes). Jupiter is about 5.2 AU from the Sun, Saturn 9.5 AU, Neptune 30.1 AU. The inner edge of the Kuiper Belt starts at about 30 AU, and the heliopause (where solar wind meets interstellar medium) is about 123 AU.
How are astronomical units used to measure space distances?
AU measures interplanetary distances within our solar system. Examples: Mercury: 0.39 AU, Venus: 0.72 AU, Earth: 1.0 AU, Mars: 1.52 AU, Jupiter: 5.2 AU, Pluto: 39.5 AU. For interstellar distances, astronomers use light-years (1 ly ≈ 63,241 AU) or parsecs (1 pc ≈ 206,265 AU). The nearest star (Proxima Centauri) is about 268,770 AU away.
How was the astronomical unit first measured?
The AU was first approximated by ancient Greek astronomers using parallax. The first precise measurement came from the 1761 and 1769 Venus transits, when astronomers worldwide timed Venus crossing the Sun to calculate Earth-Sun distance using parallax. Modern radar measurements of Venus and spacecraft telemetry provide today's exact value (149,597,870.7 km). The AU was redefined in 2012 as exactly that distance.
What is the distance from Earth to the Sun in light minutes?
Light from the Sun takes approximately 499 seconds (8 minutes 19 seconds) to reach Earth at 1 AU. This is called the light travel time. Light speed = 299,792 km/s. So 1 AU / light speed = 149,597,871 km / 299,792 km/s ≈ 499 seconds. Mars at opposition (closest) is about 3-4 light-minutes. Jupiter is about 43 light-minutes away.