"Natural Science 4" is an interactive encyclopedia that includes scientific information in the understanding of fourth grade students, wonderfully illustrated and animated.
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* Chapter 5 Lesson 26 *
* Light sources *
One of the best known and most important forms of energy is light. In its absence, nothing that surrounds us would be visible to us humans. Moreover, life on Earth, without light, would not be possible. The main source of light on our planet is the Sun. It gives us the energy we need to live.
Light travels in a straight line, in the form of a wave, at a speed of almost 300,000 kilometers per second, which means that in one second a light wave could circle the Earth more than 7 times at the Equator, and its journey from the Sun to the Earth takes about 8 minutes. It is believed that in the entire Universe, nothing can be faster than light.
All living things on earth need the light and heat of the sun in order to live. Leaves use sunlight in the process of photosynthesis, that is, in the transformation of water and mineral salts into nutrients for plants. Almost all living things depend, directly or indirectly, on photosynthesis, because without plants, life on Earth would disappear.
The sun, but also the other stars, are a natural source of light.
During the storm, when the atmosphere is dark due to the black clouds covering the sky, the lightning flashes brightly, even if for a short time. They are also natural sources of light.
Living things that glow in the dark, such as fireflies, jellyfish or some mushrooms, are also natural sources of light. But their light is very weak. You can't light up a room using fireflies.
But are natural sources of light enough for our everyday life?
Since ancient times, people have taken advantage of the sunlight throughout the day and carried out their activities unhindered. But nightfall brought with it darkness and danger. So they looked for solutions to this problem. First they discovered the fire. Torches, candles, oil or kerosene lamps were often used sources of light in ancient times. They use combustion as a chemical reaction to obtain light energy.
Over time, however, these sources of light became insufficient, and the discovery of electricity meant an important step towards the emergence of new sources of light. In fact, light sources are found all around us. The electric bulb, the neon, the flashlight, the computer or phone screen, the television are some of the artificial light sources that we always use. They are controllable, meaning we can turn them on and off when we want.
All light sources, whether natural or artificial, are called luminous bodies.
Although it has no light of its own, the Moon transmits the light received from the Sun to the Earth. Thus, it illuminates the night sky, being a secondary light source.
What other luminous bodies do you know?