What makes light visible


The sun is shining brightly after it has just rained. Even the water droplets shine through it.

Light is made up of rays that enable us to see something. For example, light rays fall on an object that sends some of the light rays back. These light rays then contain important information about the color, the shape of the object and where exactly it is located. Our eyes pick up the rays of light and pass them on to the brain. Only then can we see the object.

Without light we cannot see anything. Or to put it the other way round: the more rays of light that fall into our eyes, the better we can see. Rays of light are straight. When they hit an object, they are either swallowed, i.e. retained, or reflected, i.e. redirected in another direction. Dark colors can absorb light, light colors reflect more.

Rays of light come from light sources. The brightest light source we know is the sun. It consists of the gases hydrogen and helium and glows so strongly because hydrogen atoms are constantly combining to form helium atoms. This creates light and warmth.

Until modern times, people did not know exactly what light was. For example, they thought: You can see that rays come out of our eyes. These rays scan things and go back into the eyes.

What makes the difference when it comes to light?

Fire does not only give visible light. There are also rays with a long wavelength that we feel as warmth on the skin.

Rays of light can be thought of as tiny waves. Waves that are far apart produce red light. If the waves are closer together, yellow light is produced. Then it turns green, blue and purple. We humans can see these colors. After violet comes ultraviolet, certain animals see that. If the waves are even further apart than with red, one speaks of infrared. Other animals see that in turn. All of these colors are found in sunlight. They become visible in the rainbow. These colors are called spectral colors.

We can perceive light with our eyes as either warm or cold. Cold light has a short wavelength. It is very white, sometimes with a slight tinge of bluish or purple. Such lamps are marked as "cold-white". “Warm white” light has longer waves, it is more yellow. The light of a fire is yellow-orange. That looks warmer in our eyes. The warmth that we feel on the skin comes from the infrared rays that we cannot see with our eyes.

But this is just the beginning. Opticians have found that rays of light can be thought of as tiny waves. The narrowest waves result in atomic radiation. The X-rays are a little less narrow. Then comes the ultraviolet radiation, which causes sunburn, for example. Then follow the colors that are visible to us, from purple to red. Then comes the infrared radiation, for example the warmth of a fire. The microwaves that warm us up a little in the microwave oven, for example, are even less dense. Finally, there are the radio waves that the programs transmit to us.

What is the speed of light?

Light can travel incredibly quickly. In one second, light travels 300,000 kilometers, which is the equivalent of a billion kilometers per hour. The light therefore only needs a little more than a second from the earth to the moon.

For us humans, this speed is imperceptible. For example, when we turn on a lamp, we think the light is there immediately. When it comes to space exploration, however, the speed of light plays a very important role.

What is a light year

A light year is the length a ray of light travels in a year. A light year is around ten trillion kilometers. That's a one with 13 zeros. With “light year” you do not measure time, but a distance. Light years are mainly used to indicate great distances in space.

Anyone who speaks of light years can also calculate other lengths: light hours, light minutes or light seconds. If the sun suddenly stopped shining, we wouldn't notice until eight minutes later. So the sun is eight light minutes away from the earth. The distance to the moon is a little more than a light second.

From other stars that we see in the sky at night, the light is on the move for many years. We therefore do not see the stars as they look today, but as they used to look.

Our solar system lies in the Milky Way. It has the shape of a flat disc. At its longest point, its diameter is around 200,000 light years.