Why is the Sky Blue and the Sunset Red?

why is the sky blue and the sunset red

Sunlight from the sun passes through our atmosphere and becomes dispersed, with shorter wavelengths like blue being scattered more widely than other colors.

Blue light must travel further through the atmosphere than other colors, which explains why the sky appears blue.

Rayleigh Scattering

Sunlight passing through Earth’s atmosphere is scattered by molecules and particles in the air, typically much smaller than its wavelengths – these small airborne objects act like dichroic mirrors to scatter it quite effectively, with shorter wavelengths like blue being scattered more effectively than longer ones; hence making our sky appear blue during daytime hours.

At night, the sky is dark due to all of its scattered light having been taken up into space by darkness. At sunrise and sunset however, sunrays must travel through more atmosphere molecules before reaching their destinations, meaning even more light gets scattered around and mostly red hues emerge instead of blue. Hence why sunrises and sunsets appear particularly stunning during these times of the day.

At midday, when the sun is at its height and atmospheric clarity is relatively good, its blue light scattered by gases and particles in the atmosphere has decreased and our eyes become more attuned to red light that gives the sky its hue.

But at sunset, the sun is much closer to the horizon and must pass through more atmosphere before reaching Earth’s surface. Additionally, cloud cover acts as particle scatterers which helps the red and orange colors of sunset stand out more strongly.

Students should explore how light passes through liquids and gasses as a means of understanding why the sky changes from blue during the daytime to red at sunset/sunrise and black at night. A large glass of water, soda bottle with straw poked through its bottom or soda can with straw poked through can all serve well for this experiment; then shine a flashlight to see how that liquid or gas affects how the light travels through it; try different colored liquids or gases to see how that affects how the color of light changes – blue light should be more affected due to airborne particles than red ones; the particles being much smaller.


Our planet’s atmosphere is an astonishingly complex system. It supplies oxygen for us to breathe, water vapour for rainmaking and warmth for plant growth; but it also plays an integral part in scattering light; when light travels through it hits different molecules in the air that reflect off it in different ways and we see this reflection as blue skies – shorter lightwaves than others are more likely to scatter and be visible by your eyes.

Blue light’s frequency coincides with the natural resonant frequency of atmospheric molecules and atoms, leading to Rayleigh scattering: light that bounces around in our atmosphere is scattered more likely towards reaching our eyes than longer-wavelength lights such as red ones that tend to get absorbed by it.

At sunset or sunrise, the sun is lower in the sky and must travel through more atmosphere to reach our eyes. As more atmosphere absorbs violet and blue light is scattered away by this increased level of atmosphere, these colors become weaker while red light intensifies, giving an appearance of red to the sky.

To demonstrate Rayleigh scattering easily and simply, try this experiment: fill a tank with water, place a mirror at its base, and shine a torch into it. As longer wavelengths absorb into water molecules more effectively than shorter wavelengths, you should witness an array of blueish light beams coming from either end.

Blue light from the Sun travels through our atmosphere and is mostly reflected back to us, while other colors scatter more or are absorbed less; this gives the sky its typical blue hue. However, at sunrise or sunset the Sun must traverse further through a thicker layer that contains more dust; this decreases violet and blue light being deflected away from our eyes, hence why the sky appears red at these times.


The Earth’s atmosphere is an amazing feat of creation that provides many essential services: oxygen to breath, water vapour that brings rain and air conditioning, carbon dioxide that allows plants to flourish, and beautiful hues in the sky. Because gases and particles in its upper layer are small compared to wavelengths of light, they scatter sunlight differently; blue hues tend to be scattered more widely, leading to its appearance during daylight hours as the sky appears bluer than other hues.

Red and orange wavelengths tend to scatter less, leading to red sky during sunsets. This phenomenon happens due to the sun being lower in the sky at dusk than during day, forcing light through longer pathways through our atmosphere – it increases chances that longer wavelengths like red and orange may get scattered by nature.

Mie scattering explains why clouds appear white: water vapor scatters light more effectively than nitrogen and oxygen molecules do, spreading light throughout its visible spectrum from blue to red simultaneously resulting in clouds appearing white.

Sunset skies may appear redder when volcanic eruptions or forest fires emit sulphate aerosols; these microscopic particles scatter red and orange light more readily than blue light wavelengths, creating reddish sunsets and sunrises even though there may still be plenty of blue in them.

At home, you can conduct this experiment by shining a beam of white light through clear liquid with small quantities of soap or milk mixed in. From the side, this beam appears bluish-white; when looked directly from its end though, it becomes reddish-orange due to more strongly scattered short wavelengths being blue than longer red wavelengths, giving rise to blue transmission during daytime hours and yellowish orange reflection during sunset and sunrise hours.


Light appears blue because its photons pass through air molecules and get scattered, but light can also be reflected off water droplets in clouds and open water, with this reflection having different results from scattering: it bends sunlight into different hues and subtly alters its hue, producing what gives blue skies their hue as well as sunsets with their distinct red or orange tints.

Sunlight that has been scattered blue through the atmosphere appears yellowish-orange on bodies of water because its wavelengths more closely match up with their absorption spectrum – this phenomenon accounts for why seas and oceans appear blue even without blue skies overhead.

At sunset and sunrise, when the sun travels lower in the sky it must travel through an increased thickness of atmosphere, which causes its shorter blue wavelengths to dissipate into yellowish-orange wavelengths instead. As a result, its color appears more yellowish-orange during these times of day.

The Sun is a yellow dwarf star, meaning that it has less mass than larger stars of its class and therefore can be more easily observed with telescopes and spacecraft. Due to Rayleigh Scattering, most of the light that reaches our eyes from it appears blue-tinged; however, all colors in its rainbow spectrum are present in its spectrum of light rays.

If you were floating through space or the Moon, the sun would appear white as its light would not be scattered by any atmosphere to scatter. On Earth however, its atmosphere causes its light to appear yellowish-orange at sunset and red at sunrise.

At its heart, blue skies occur because violet and blue wavelengths scatter more widely than any other colors. This explains why sunset light appears yellow while sunrise illumination seems redr. Other colors travel straight through our atmosphere from sunlight source to eyes without deviating, creating less striking results than their counterparts would suggest.

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