Complex sentence: A light-year (symbol: ly), sometimes written light year or lightyear is an astronomical unit of length (not time) equal to just under 9.5 trillion kilometres (or about 6 trillion miles).
Split into simpler sentences: A light-year (symbol: ly), sometimes written light year or lightyear is a unit of length (not time) used in astronomy. It is equal to just under 9.5 trillion kilometres (or about 6 trillion miles).