In this section I will be explaining a few basic aspects of light: what is it really? How does it move? What is its speed? What is the use of this speed? Why can’t anything go faster than it?

Light is made up of particles called photons. This name was given to them by Einstein. Its mass is of 0 (it doesn’t weigh anything). Photons are particles released when energy is produced.
A photon is a particle who moves in a wave. This is a unique factor in science. It is difficult to admit it, but there you have it. Sometimes in science you have to accept things that may seem absurd, such as four-dimensional space.
Light moves at a speed a little under 300 000 km per second. It may seem huge, but when the closest star to the sun, which is Proxima Centauri, is located 4 light years away (its light takes four years to reach us.)
A light year isn’t a speed unit, but a distance unit.
Here comes the most scientific part of this entry: Why can’t anything go faster than light? This was answered by Einstein thanks to his famous equation E=MC2.
To accelerate, you need energy. But this energy adds up to your mass. So the more energy you put in for accelerating, the more you will weigh. And the more you weigh, the more energy is needed to make you continue accelerating. This is only visible at speeds close to the speed of light.
Eventually, you arrive at a point where the energy needed to make you continue accelerating is infinite. This is why a photon, which weighs nothing, is the only thing capable of reaching such a speed, as no mass is added to its initial one. However you can slow down light. 300 000 km/s is the speed of light in space. Because the atmosphere is denser than space, light has more difficulty passing.
Light, in outer space, will ALWAYS travel at around 300 000 km/s. Even if you are in a spacecraft moving at lets say half the speed of light, the light emitted by your the front lights of your spacecraft will travel at 300 000 km/s, and the same speed for the back lights. Any other object would go at 150 000 km/s + the speed at which it was “shot” in the case of the front lights and 150 000 - the speed at which it was “shot” in the case of the rear lights.
This means that light is independent from the speed at which it is emitted.

Thanks to this speed far away objects, from which light departed lets say 2 million years ago, appear to us as they were 2 million years ago. In other words, this is a voyage into the past (unfortunately there is no way to predict the future.) In the nearest galaxy, the Andromeda Galaxy, our own earth appears as it was during the dinosaurs!