Rosa Parks sparks Civil Rights Movement. On this day in 1955, Rosa Parks, an African-American, was arrested and charged with violating a Montgomery, Ala., ordinance that required her to relinquish her bus seat to a white passenger. Her act of defiance sparked a yearlong bus boycott in the segregated city.
View full size image. The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light. In miles per hour, light speed is, well, a lot: about 670,616,629 mph. If you could travel at the speed of light, you could go around the Earth 7.5 times in one second.
Of course, Galileo points out that in fact nothing about the speed of light can be deduced from this observation, except that light moves faster than sound. He then goes on to suggest a possible way to measure the speed of light. The idea is to have two people far away from each other, with covered lanterns. One uncovers his lantern, then the other immediately uncovers his on seeing the light from the first.