Light Does not Always Travel Very Fast

Nothing travels faster than light. Thats something we hear bandied about quite a lot. Another is, Light is a constant. We can measure everything alongside it. Sometimes we hear that light can have its direction of travel altered, e.g. when it passes close to a star. The truth is that light can end up going quite slowly and it is not quite the constant many believe it is. What people mean to say, or should rather express, is that light travels at a constant speed in a vacuum. Without this essential qualification we soon see that light is anything but a constant. In a vacuum light travels at 186,000 miles per second, (300,000 km per second).