The parsec -LRB- `` parallax of one arcsecond '' , symbol pc -RRB- is a unit of length , equal to just under NUMBER@1 trillion kilometres -LRB- about NUMBER@2 trillion miles -RRB- , or about NUMBER@3 light-years .

One parsec is the distance that light will travel in NUMBER@3 years , or just under NUMBER@1 trillion kilometres -LRB- about NUMBER@2 trillion miles -RRB- .
