length · International · Modern
SI base unit of length. Its definition fixes the speed of light in vacuum at exactly 299,792,458 m/s, with the second defined from the caesium-133 hyperfine frequency.
Converter
length · International · Modern
light-year
lyexact
- Record
- M271
- Definition quality
- Standardized
- Conversion mode
- multiplicative
- Calculator
- Fully calculable
Store the explicit Julian-year convention so 'year' is never ambiguous.
Definition
For this project, one light-year is the distance light travels in one Julian year of exactly 365.25 days: 9,460,730,472,580,800 m.
Reference value
One light-year is equal to 9.460730 × 10^+15 metres.
History & use
Astronomers use it as a convenient stellar-distance unit; the calculator definition combines the exact SI speed of light with the IAU Julian year.
Modern use
Common in astronomy education and popular descriptions of stellar/galactic distances.
Did you know?
A light-year measures distance, not time.
Sources & evidence
Source tier Tier A · confidence High
Related measurements
length · International · Modern
1 km = 1000 m by the SI prefix kilo-.
length · International · Modern
1 cm = 0.01 m by the SI prefix centi-.
length · International · Modern
1 mm = 0.001 m by the SI prefix milli-.
inch
inlength · UK / US · Modern / historical
1 international inch = exactly 0.0254 m.
foot
ftlength · UK / US · Modern / historical
1 international foot = exactly 0.3048 m.
yard
ydlength · UK / US · Modern / historical
1 international yard = exactly 0.9144 m.
mile
milength · UK / US · Modern / historical
1 international mile = exactly 1609.344 m = 1760 yd.