Light is a form of energy that travels as an electromagnetic wave: tiny electric and magnetic fields that push each other forward through space. It needs no air or water to travel.
The fastest thing there is
In empty space, light travels 299,792,458 metres every second. Nothing that carries information can go faster.
- Light from the Moon reaches us in about 1.3 seconds.
- Light from the Sun takes about 8 minutes 20 seconds.
Wave or particle? Both
Sometimes light acts like a wave (it spreads, bends and makes patterns). Sometimes it acts like a stream of particles called photons. A photon has no mass but carries energy. Bluer light has more energy per photon than redder light.
The colours we can see are a tiny slice
Visible light is only a small part of the electromagnetic spectrum:
radio waves → microwaves → infrared → visible light → ultraviolet → X-rays → gamma rays
Your Wi-Fi, a microwave oven and an X-ray machine all use the same thing as light, just at different wavelengths.
Why is the sky blue?
Sunlight contains all colours. Air molecules scatter short (blue) wavelengths much more than long (red) ones, so blue light comes at you from every direction in the sky. At sunset, light passes through much more air, the blue is scattered away, and the reds and oranges are left.