Light-year ly
About the Light-year
A light-year is the distance light travels in vacuum in one Julian year of 365.25 days, which works out at exactly 9,460,730,472,580,800 metres, about 9.46 trillion km. It is about 63,241 astronomical units. Professional astronomers usually prefer the parsec, but the light-year dominates popular writing.
Related Units
Astronomical unit
au149,597,870,700 m (exact)
The astronomical unit is roughly the mean distance from the Earth to the Sun. Since the IAU's 2012 Resolution B2 it is...
Parsec
pc648,000/π au ≈ 3.0857 × 10¹⁶ m
A parsec is the distance at which one astronomical unit subtends an angle of one arcsecond, making it 648,000/π au...
Metre
mBase unit; c = 299,792,458 m/s exactly
The metre is the length of the path travelled by light in vacuum in 1/299,792,458 of a second. It was first defined by...
Ångström
Å1 Å = 10⁻¹⁰ m = 0.1 nm (exact)
The ångström equals one ten-billionth of a metre, roughly the size of an atom. It is named after the Swedish physicist...