Light Years
Unlike our calendar year, which measures time, a light year is used to measure distances
in space. A light year is the distance light travels in one year. To us, light seems to travel
almost instantly - if you shine a flashlight at someone, they see it right away. But light
does take time to travel - it is just too fast for you or I to notice. Light travels at 300,000
kilometers per second. So a light year is about 9,460,800,000,000 kilometers (a long,
long way away!) Alpha Centauri and Proxima Centauri, the stars nearest our solar
system, are about 4.3 light-years away (roughly 38,000,000,000,000 kilometers away.)
This means that if you shone a flashlight at one of these stars, it would takemore than
four years for the light to reach them. To give you an idea of how fast light actually
travels: it could circle the equator of Earth seven times in just one second! Our own sun is
about 8 lieght minutes away.