In recent centuries, physicists studied the phenomenon of light and explained the mystery that surrounded it: light is the small visible portion of the electromagnetic spectrum. Comprised of vibrating units of energy (quanta), it is transmitted in waves by a light source. It takes a defined length of time to travel from the point where it is generated to the eye of the observer.

Every wavelength is defined by a spectral colour. The spectrum of sunlight is made up of continuous transitions – from short-wave violet through blue, green and orange to long-wave red. Beyond this range, rays cannot be "seen" by the human eye; gamma, X, ultraviolet and infrared rays are not visible.

Speed of light: 300,000 km/s

The time it takes light to travel from an object to the observer's eye is determined by the speed of light. In 1850, the French physicist Leon Foucault developed an experimental array with a rotating mirror that enabled the speed of light to be precisely determined: 2.98 x 10⁸ m/s. For the speed of light in a vacuum and in air, the rounded value of 3 x 10⁸ m/s – i.e. 300,000 kilometres a second – is normally used.

So light travels faster than anything else known to science. It reaches the Earth from the Moon in around 1.3 seconds, covers the 150 million kilometres from the Sun in 8^1/3 minutes and takes 4.3 years to travel from the nearest fixed star, Alpha in Centaurus. If Alpha exploded today, we would not find out for nearly half a decade.