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Perfect for astronomy students, space enthusiasts, and science educators. Results update in real-time and can be shared via URL.\n\nValue\n\nFrom kilometer lightyear parsec meter mile\n\nTo kilometer lightyear parsec meter mile\n\nResult\n\nYour recent:\n\nCopied!\n\n## Astronomical Distance Formulas\n\n**1 AU:** `149,597,870.7 km`\n\n**1 light-year:** `9.461 × 10¹² km`\n\n**1 parsec:** `3.0857 × 10¹³ km`\n\n**1 pc → ly:** `× 3.2616`\n\n**1 ly → AU:** `× 63,241`\n\n**1 pc → AU:** `× 206,265`\n\n## Cosmic Distance Scale\n\nObject / DistancekmAULight-YearsParsecs Earth → Moon384,4000.002574.07 × 10⁻⁸1.25 × 10⁻⁸ Earth → Sun1.496 × 10⁸11.58 × 10⁻⁵4.85 × 10⁻⁶ Earth → Mars (closest)5.46 × 10⁷0.375.77 × 10⁻⁶1.77 × 10⁻⁶ Earth → Jupiter5.88 × 10⁸3.936.22 × 10⁻⁵1.91 × 10⁻⁵ Sun → Neptune4.5 × 10⁹30.074.76 × 10⁻⁴1.46 × 10⁻⁴ Sun → Voyager 1 (2024)~2.4 × 10¹⁰~1620.002577.88 × 10⁻⁴ Sun → Proxima Centauri4.02 × 10¹³268,7704.2461.301 Sun → Sirius8.13 × 10¹³543,8708.602.64 Milky Way diameter~10¹⁸~6.65 × 10⁹~105,700~32,400 → Andromeda Galaxy2.4 × 10¹⁹1.6 × 10¹¹2,537,000778,000 Observable universe radius4.4 × 10²³2.94 × 10¹⁵46.5 billion14.26 Gpc\n\n## Light Travel Times\n\nJourneyLight Travel Time Earth → Moon~1.28 seconds Earth → Sun~8.3 minutes Earth → Mars (closest)~3 minutes Earth → Jupiter~33 minutes Sun → Neptune~4.2 hours Sun → Proxima Centauri~4.25 years Across Milky Way~105,700 years To Andromeda Galaxy~2.5 million years\n\n## Frequently Asked Questions\n\n### How far is a light-year in kilometers?\n\n**9.461 × 10¹² km** (about 9.461 trillion km or 5.879 trillion miles). Light travels at 299,792,458 m/s. Over one Julian year (365.25 days), that adds up to ~9.461 trillion km.\n\n### What is a parsec?\n\nA parsec = the distance where **1 AU subtends 1 arcsecond** of parallax. 1 pc ≈ 3.2616 ly ≈ 30.857 trillion km. Astronomers prefer parsecs because they relate directly to parallax measurements from telescopes.\n\n### What is an astronomical unit (AU)?\n\n1 AU = exactly **149,597,870,700 meters** (~149.6 million km). Originally the mean Earth-Sun distance; now defined as a fixed constant by the IAU (2012). Used for solar system distances.\n\n### How many light-years away is the nearest star?\n\n**Proxima Centauri**: 4.246 light-years (1.301 pc). Part of the Alpha Centauri triple system. At the speed of Voyager 1 (~17 km/s), the trip would take ~73,000 years.\n\n### What is the observable universe size?\n\nRadius: **46.5 billion light-years** (14.26 Gpc). The universe is 13.8 billion years old, but space itself has been expanding — the most distant objects are now far beyond 13.8 billion ly away.\n\n### What is the best free astronomical unit converter?\n\nThis free astronomical distance converter handles light-years, parsecs, astronomical units, kilometers, and miles with instant results. It uses IAU-standard conversion factors and requires no downloads.\n\n### Can I use this astronomical converter without signing up?\n\nYes. This converter is completely free with no account or registration needed. Enter a value, pick your units, and get the result instantly — all calculations run privately in your browser.\n\n### Key Facts\n\n- 🌌 Speed of light: 299,792,458 m/s (exact, defining constant)\n- 🌌 1 AU ≈ 8.3 light-minutes\n- 🌌 Nearest star (Proxima Centauri): 4.25 ly\n- 🌌 Milky Way diameter: ~105,700 ly\n- 🌌 Observable universe: ~93 billion ly across\n- 🌌 \"Parsec\" = **par**allax + arc**sec**ond\n\n## Related Products\n\n[🔭 Telescopes →](https://www.amazon.com/s?k=telescope%20astronomy%20beginner\u0026tag=tejji-20) [🌌 Astronomy Binoculars →](https://www.amazon.com/s?k=astronomy%20binoculars%20stargazing\u0026tag=tejji-20) [📚 Astronomy Books →](https://www.amazon.com/s?k=astronomy%20book%20beginner\u0026tag=tejji-20)\n\n*As an Amazon Associate, tejji.com earns from qualifying purchases.*\n\n### Distance Measurement History\n\n- **~240 BC:** Eratosthenes estimates Earth's circumference\n- **1672:** Cassini measures Mars parallax → first AU estimate\n- **1838:** Bessel measures first stellar parallax (61 Cygni)\n- **1913:** Parsec unit introduced by Turner\n- **1958:** IAU standardizes AU value\n- **2012:** IAU redefines AU as exact constant\n\n### Related Conversions\n\n[📏 Length Conversion](/convert/length-conversion) [📐 Length (Metric) Conversion](/convert/length-metric-conversion) [🏎️ Speed Conversion](/convert/speed-conversion) [🔄 All Converters](/convert)\n\n[All unit converters →](/convert)\n\n📱\n\nQuick Access\n\nInstall this tool on your device for instant access\n\nInstall App\n\n- Temperature\n- [Temperature](/convert/temperature-conversion)\n\n\u003c!--THE END--\u003e\n\n- Length\n- [Length](/convert/length-conversion)\n\n\u003c!--THE END--\u003e\n\n- Length (Metric)\n- [Length (Metric)](/convert/length-metric-conversion)\n\n\u003c!--THE END--\u003e\n\n- Metric\n- [Metric](/convert/metric-conversion)\n\n\u003c!--THE END--\u003e\n\n- Bytes\n- [Bytes](/convert/bytes-conversion)\n\n\u003c!--THE END--\u003e\n\n- Bytes Widgets\n- [Bytes Widgets](/convert/bytes-conversion/widgets)\n\n\u003c!--THE END--\u003e\n\n- Number\n- [Number](/convert/number-conversion)\n\n\u003c!--THE END--\u003e\n\n- Angle\n- [Angle](/convert/angle-conversion)\n\n\u003c!--THE END--\u003e\n\n- Astronomical\n- [Astronomical](/convert/astronomical-conversion)\n\n\u003c!--THE END--\u003e\n\n- Frequency\n- [Frequency](/convert/frequency-conversion)\n\n\u003c!--THE END--\u003e\n\n- Mileage\n- [Mileage](/convert/mileage-conversion)\n\n\u003c!--THE END--\u003e\n\n- Mass / Weight\n- [Mass / Weight](/convert/mass-conversion)\n\n\u003c!--THE END--\u003e\n\n- Mass (Metric)\n- [Mass (Metric)](/convert/mass-metric-conversion)\n\n\u003c!--THE END--\u003e\n\n- Speed\n- [Speed](/convert/speed-conversion)","footer":"\n\n📱 Install Tejji for quick access to this tool Install\n\nTools\n\n- [All Apps](/apps/)\n- [Converters](/convert/)\n- [IP Tools](/ip/)\n- [Calculator](/apps/calculator)\n\nExplore\n\n- [Time \u0026 Date](/time-date/)\n- [Postal Codes](/zip-codes/)\n- [Typing](/typing/)\n- [Extensions](/browser/chrome/extensions/)\n\nCompany\n\n- [About](/home/about)\n- [Contact](/home/contact)\n- [Privacy](/home/privacy)\n- [Terms](/home/terms)\n\nSupport\n\n- [Feedback](/home/contact)\n- [Buy me a coffee](https://buymeacoffee.com/tejji)\n\n© 2026 [Tejji.com](/) — Free online tools for everyone.\n\nWe use cookies for analytics and ads. By clicking \"Accept\", you consent to our use of cookies. [Privacy Policy](/home/privacy)\n\nReject Accept"},"metadata":{"title":"1 lightyear in kilometer | Astronomical Conversion | Tejji","description":"Free online astronomical distance converter — convert between light-years, parsecs, astronomical units, kilometers, and miles instantly, no sign-up required. Includes cosmic scale chart and space distance comparisons. Works on all devices.","imageUrl":"https://tejji.com/page/og-default.png","author":null,"published":null,"modified":null},"rate":{"price":{"priceMicros":0,"currency":""},"license":{"cuid":"","licenseType":"","licensePath":"","permissions":[],"validUntil":""},"error":""}}]