Light Year & Astronomical Distance Calculator
Convert astronomical distances between light years, parsecs, astronomical units, and kilometres. Calculate travel times at any spacecraft speed.
Astronomical Distance Guide
Standard Distance Units
Astronomical Unit (AU): mean Earth-Sun distance. 1 AU = 149,597,870 km ≈ 150 million km. Light travel time: 8 minutes 19 seconds. Used for distances within the solar system. Mars: 1.5 AU. Jupiter: 5.2 AU. Pluto: 39 AU. Voyager 1: ~165 AU and counting. Light Year (ly): distance light travels in one year. 1 ly = 9.461 × 10¹² km = 63,241 AU. Used for stellar distances. Light-second: 299,792 km. Light-minute: 18 million km. Light-hour: 1.08 billion km. Parsec (pc): defined from parallax. 1 pc = 3.26
Familiar Astronomical Distances
Moon: 1.28 light-seconds (384,000 km). Sun: 8.3 light-minutes. Mars (closest approach): 3.0 light-minutes. Jupiter: 35 light-minutes. Pluto: 5.3 light-hours. Voyager 1 (current): ~21 light-hours. Heliopause (edge of solar system): ~1 light-day. Nearest star Proxima Centauri: 4.24 light-years. Visible stars (naked eye): mostly 10-1000 ly. Centre of Milky Way: 26,000 ly. Edge of Milky Way disk: 50,000 ly. Andromeda Galaxy (M31): 2.5 million ly. Virgo Cluster: 65 million ly. Edge of observable univ
Travel Times — Reality Check
Voyager 1 speed: 17 km/s = 0.0057% of light speed. Years to reach Proxima Centauri at this speed: 74,000 years. Fastest spacecraft (Parker Solar Probe): 200 km/s = 0.067% of c. To Proxima Centauri: 6,300 years. Theoretical 10% of c spacecraft (light sail, fusion drive): 42 years to Proxima. Theoretical 99% of c: 4.3 years coordinated time. Less for crew due to time dilation. Reality: chemical rockets cannot reach significant fraction of c. Ion drives, light sails, nuclear pulse propulsion, theor
Looking Back in Time
Light takes time to travel — looking at distant objects means looking back in time. Sun: see it as it was 8 minutes ago. If Sun vanished now, we'd notice in 8 minutes. Proxima Centauri: see it as it was 4.24 years ago. Andromeda Galaxy: see it as it was 2.5 million years ago. Most distant observable galaxies (z > 11): seen as they were 13+ billion years ago — light from when the universe was young. Cosmic Microwave Background: oldest light visible. From 380,000 years after the Big Bang. We canno
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