Convert Space Distances — AU, Light-Years & Parsecs Convert between kilometers, miles, astronomical units (AU), light-years, and parsecs.
Astronomical Distance Converter
Convert between kilometers, miles, astronomical units (AU), light-years, and parsecs.
Enter a distance
Type the astronomical distance value.
Select units
Choose between km, mi, AU, light-years, and parsecs.
Review the converted distances
Converted distance appears with appropriate precision.
What Is Astronomical Distance Converter?
An astronomical distance converter translates between units used to measure the vast distances in space. Kilometers and miles quickly become impractical for cosmic scales, so astronomers use specialized units. The Astronomical Unit (AU) is the mean Earth-Sun distance (~150 million km). The light-year (ly) is the distance light travels in one year (~9.46 trillion km). The parsec (pc), defined by the parallax method, equals about 3.26 light-years. These units make cosmic distances comprehensible: the nearest star is 4.24 ly away, the Milky Way is ~100,000 ly across, and the observable universe is ~46 billion ly in radius.
Why Use Astronomical Distance Converter?
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Covers all major astronomical distance units.
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Handles the enormous numbers involved in cosmic distances.
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Real-time conversion with appropriate precision.
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Educational reference table with notable cosmic distances.
Common Use Cases
Astronomy Education
Convert between units for homework, research papers, and presentations.
Science Communication
Express cosmic distances in relatable units for articles and documentaries.
Astrophysics
Translate observational data across different distance measurement systems.
Space Enthusiasts
Explore and compare cosmic distances for personal interest.
Technical Guide
Astronomical distance units:
• 1 AU = 149,597,870.7 km (exact IAU definition)
The mean Earth-Sun distance. Light crosses 1 AU in about 8 minutes 19 seconds.
• 1 light-year = 9.4607 × 10¹² km
The distance light travels in one Julian year (365.25 days). Not a unit of time!
• 1 parsec = 3.0857 × 10¹³ km ≈ 3.2616 ly
Defined as the distance at which one AU subtends one arcsecond of parallax. The word combines "parallax" and "arcsecond."
Notable distances:
• Moon: 0.00257 AU = 384,400 km
• Mars (closest): ~0.52 AU
• Jupiter: ~5.2 AU
• Proxima Centauri: 4.246 ly = 1.301 pc
• Andromeda Galaxy: 2.537 million ly = 778 kpc
• Observable universe radius: ~46.5 billion ly
Tips & Best Practices
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11 parsec ≈ 3.26 light-years. Parsecs are preferred in professional astronomy.
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2Light takes 8 minutes 19 seconds to travel 1 AU (Earth to Sun).
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3The nearest star system (Alpha Centauri) is about 4.37 light-years away.
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4When dealing with galaxies, use kiloparsecs (kpc) or megaparsecs (Mpc).
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⚖️ Unit ConvertersFrequently Asked Questions
Q How far is one light-year in kilometers?
Q What is an astronomical unit (AU)?
Q What is a parsec?
Q How far away is the nearest star?
Q Is a light-year a measure of time?
About This Tool
Astronomical Distance Converter is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.