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
astronomical unit
auexact
- Record
- M270
- Definition quality
- Standardized
- Conversion mode
- multiplicative
- Calculator
- Fully calculable
Definition
Astronomical unit: exactly 149,597,870,700 metres under IAU 2012 Resolution B2.
Reference value
One astronomical unit is equal to 149,600,000,000 metres.
History & use
The AU long served as a solar-system distance scale; in 2012 the IAU replaced its older dynamical definition with a fixed exact SI length.
Modern use
Standard astronomical distance unit, especially within planetary systems.
Did you know?
Before 2012 its SI length was observationally determined; today the metre value is exact.
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.