Light travels at 186,300 miles per second. That means that if light could follow the curvature of the Earth (which it cannot, it travels in a straight line) and one turned on a light bulb at the Equator, the resulting light would travel around the Earth (25,000 miles at the Equator) seven and one-half times in one second.

A Light-Year is the distance that light travels in one year.

Note: Light travels in a straight line if not impeded. However, light can be bent, deflected and reflected by other matter. Einstein theorized and scientist have proven that light is "bent" by gravitional forces. Light from far away sources is significantly "bent" by the huge masses found in the Universe. Astronomers sometimes refer to such bending as "displacement." Displacement causes far away stellar objects to appear in one place but actually be in another.