Why is the sky red at night?
Blue no longer reaches us! The white light of the Sun is made up of the seven colors of the rainbow. During the day the atmosphere scatters the blue color of this light.
In the evening, sunlight hits the Earth on the horizon: it then penetrates a thick layer of air. This air acts as a filter, the denser it is, the stronger the colors.
But red passes because it is less filtered! If the atmosphere was denser, the sky would be red-orange all day.
Create a rainbow?
Do you think sunlight is white? In fact, it includes all colors. It’s easy to see. It needs smooth, transparent glass. Fill it with water and keep it in the sun on a white sheet.
You will see a small rainbow on the leaf. The glass of water splits the colors of the light as well as the atmosphere. After the storm we can see a beautiful rainbow. Just like water drops in the sky!
Make the television bigger.
The white color that comes from the sun or elsewhere is the union of all the colors. Look at an old television screen with a magnifying glass. You’ll see small blue, green, or red spots.
These are the colors we call primary colors because mixing gives us all the other colors.
For example, look at a yellow dot on the screen – you’ll see that only the blue and green dots are lit. And when the points light up: knows everything!
If I were on mars?
In the evening the sun will be blue, surrounded by green skies! The sky of Mars is pinkish-orange during the day, because the air is different from ours.
The atmosphere of Mars contains a lot of carbon dioxide, while the atmosphere of Earth consists mainly of oxygen and nitrogen.
On the Moon, the sky remains dark because there is no atmosphere that can filter out the colors of the Sun;
The environment in which we live and breathe produces spectacular phenomena like mirages, rainbows, etc. However, we do know of many other phenomena that are just as surprising as we often take for granted.
“The sky is blue” is an observation that can be made every day (at least on a clear day!) but this apparent banter shouldn’t stop us from asking ourselves:
“Why is the sky blue?” Similarly to “Why is the night dark?” This is a question that may sound naive, but we will see that it is not. The answers to these questions will allow us to discover amazing physical and celestial phenomena!
Why is the sky blue?
The sky is blue when seen during the day and on a clear day. For a long time it was believed that the blue color of the sky was due to the scattering (i.e. deflection) of light by the dust in the air.
It is also assumed that very pure (dust-free) air does not propagate light. We know today that Rayleigh found the correct explanation in 1899.
Diffusion is mainly due to the air molecules themselves.
The atmosphere is illuminated by the light emitted by the surface of the Sun.
When this white light reaches a molecule of air (nitrogen: N2 or oxygen: mainly O2), it breaks down into different “colors”.
Every radiation (each “color”) is absorbed by the molecule and then re-emitted in all directions.
However, the intensity of the re-emitted light depends on the wavelength (colour) and the direction of observation (are we directed at 90 degrees towards the source?)
We see that when we are on the axis of illumination (direction of the sun). and vice versa when we are in a direction perpendicular to this axis then red color is more re-emission than blue color.
When we are on the axis of light, the air molecule illuminated by the Sun gives us red colored light and when we look vertically it is more dimmer.
The light emitted by each molecule “collides” with other molecules in the air and the same phenomenon is repeated: the light transmitted in the direction of illumination is richer in red, while the light scattered laterally is richer in blue. This property explains the blue color of the sky.
If we lived on a planet with no atmosphere, sunlight would not spread and we would have a dark sky, consisting only of the Sun, the Moon and the stars.
Why are sunsets red?
When we look at the Sun, we are looking “into the axis of knowledge”. From above, the transmitted light becomes richer in red and ends up in blue.
So we see the Sun redder than it actually is, but the effect is negligible.
You also want to know about:
- Why is it yellow outside
- Why is Venus so hot