Light waves
Light travels in waves — but what is a wave? You can make a wave by shaking one end of a ribbon. The up and down movement you make spreads along the length of the ribbon and appears as a wave. A wave is a way in which energy can move from one place to another. Light waves travel at an astonishing speed, faster than anything else we know.
The distance between the top of one wave and the next is known as the ‘wavelength’. The depth of a wave is called its ‘amplitude’. Each colour of the spectrum has its own special wavelength and amplitude.
Measuring with light
Both large and small distances can be measured very accurately with laser light. In 1969, the Apollo II astronauts placed a mirror on the Moon. Scientists on Earth shone a laser beam towards the mirror and timed how long it took for the beam to be reflected back again. They knew the speed at which the light travelled and so they were able to work out the distance of the Moon from the Earth — to within just a few centimetres of the actual distance!
Picture Credit : Google