Define light year and explain how and why light years are used to measure distances in the universe

Light year by definition is the astronomical measurement showing how fast light travels in a year. The speed of light is 299 792 458 metres/second so in a year it can travel over 6 million million miles! 
Light years are used to measure distances in the universe because the universe is massive! 

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.

Iwould sure like to answer your question but i honestly just don’t know