Kilometers to Light-years (km to ly)
1 kilometer equals 1.057000834×10⁻¹³ light-years (rounded).
How to convert kilometers to light-years
To convert kilometers to light-years, multiply the number of kilometers by 1.057000834×10⁻¹³. The factor is rounded to 10 significant digits. To go the other way, multiply light-years by 9,460,730,472,581 (rounded).
light-years = kilometers × 1.057000834×10⁻¹³
Example: 10 kilometers = 1.057000834×10⁻¹² light-years.
About these units
Kilometer (km)
1,000 meters. The standard unit for road distances in most countries.
A name for 1,000 meters took a while to settle. In 1793 France's National Convention made the metre the sole French unit of length, and the first proposed name for the thousand-metre multiple was millaire. Everyday French usage then leaned on the myriametre, 10,000 meters, well into the 1800s. The Netherlands adopted the kilometre in 1817, under the local name mijl, and made it the only official unit of that size in 1867. In 1935 the CIPM dropped the myria- prefix, which left the kilometre as the standard unit for road-scale distances.
Kilo- is the SI prefix for a thousand, and the kilometre is now the preferred unit for land distances in most of the world, with the United States, the United Kingdom and Liberia among those that still use the mile. One kilometre is about 0.621 mile. The main span of Lisbon's 25 de Abril Bridge, at 1.013 km, gives a sense of the scale. Even its pronunciation has been argued over: in 1970 Australia's Metric Conversion Board made stress on the first syllable official, although Prime Minister Gough Whitlam argued for stress on the second. Military slang in several countries calls it a klick.
1 kilometer = 1,000 meters (exactly).
Sources: Wikipedia: Kilometre; Wikipedia: Metric prefix; BIPM: history of the metre
Light-year (ly)
The distance light travels in one Julian year: exactly 9,460,730,472,580,800 meters (about 9.46 trillion km).
Despite the name, a light-year measures distance rather than time, and its coinage is a little later than most people assume. Friedrich Bessel measured the distance to the star 61 Cygni in 1838 but did not use the unit himself. The light-year appeared in print in 1851, in a German article by Otto Ule, who explained its odd use of a time word by comparing it to saying that a place is an hour's walk away.
The International Astronomical Union defines it as the distance light travels in a vacuum in one Julian year of 365.25 days, about 9.46 trillion kilometers. NIST lists it as 9.460 73 times 10 to the 15th meters. Light-years dominate popular science, while professional astronomers mostly prefer the parsec, about 3.26 light-years. For scale, Proxima Centauri, the nearest star to the Sun, is about 4.24 light-years away, and the Milky Way is roughly 100,000 light-years across.
1 light-year = 9.460730473×10¹⁵ meters (approximately).
Sources: Wikipedia: Light-year; NIST Guide to the SI, Appendix B.8: conversion factors
Related conversions
- Light-years to kilometers (reverse)
- Kilometers to meters
- Kilometers to centimeters
- Kilometers to millimeters
- Kilometers to inches
- Kilometers to feet
- Kilometers to yards
- Kilometers to miles
- Kilometers to micrometers
- Kilometers to nanometers
- Kilometers to nautical miles
- Kilometers to pixels (CSS)
- Kilometers to picometers
- Meters to light-years
- Centimeters to light-years
- Millimeters to light-years
- Inches to light-years
- Feet to light-years
- Yards to light-years
- Miles to light-years
- Micrometers to light-years
- Nanometers to light-years
- Nautical miles to light-years
- Pixels (CSS) to light-years
See all length units.