6.02 Faster Than the Speed of Light

The sun's light travels. It moves from point A, the sun, to point B, the Earth.

All light travels, even the light from your lamp. Light moves really, really fast. It's the fastest thing in the universe.

Imagine traveling around Earth seven and a half times in one second, that is how fast light travels! This is why light appears to instantly fill a room when you turn on a lamp and why you can see when someone turns on a flashlight even when they are far away.

Light is emitted in all directions from its source, which is why so much of the Earth receives sunlight at one time.

Light can move through a few objects fairly easily. We call an object like this a medium, which is a fancy word for material. If you have more than one medium, we call them media—not mediums. 

Air, water, and glass are examples of different media that light can travel through. Different materials or media have different properties, which means they interact with light differently. In most cases, when light moves from one medium to another, the light changes direction.

When light strikes an object or surface, one of three things will happen to it. What happens to it depends on whether the object it strikes is transparent, translucent, or opaque. 

Nothing else in the universe moves quite like light. It is the fastest thing scientists have ever discovered, and it can only travel in straight lines. It passes through some media and is absorbed and reflected by others. Light can either pass through transparent objects or be absorbed and reflected off opaque objects. Only some light passes through translucent objects.