Physics – Why is the Sky Blue and Sunsets Red?

why is the sky blue and sunsets red physics

As sunlight travels through the atmosphere, its light is scattered by air molecules and particles, with shorter wavelengths such as violet and blue being dispersed more widely than longer ones (red).

Sky blue color comes from sunlight which has passed through our atmosphere; lunar illumination does not have this same impact, since its beam hasn’t passed through it.

Light is a spectrum

Light from the Sun contains all of the colors of the visible spectrum and, when separated through a prism, adds up to white light. However, when sunlight travels through Earth’s atmosphere it doesn’t remain pure white due to molecules and dust particles in the atmosphere scattering and attenuating (removing) certain wavelengths faster) which means sky appears bluer while sunsets look redder than expected. This process is known as bulk attenuation – hence why sunsets appear red.

Light travels along a straight path until it strikes an object such as dust particles or gas molecules, then is scattered off in different directions – this process is called Rayleigh scattering and is what gives the sky its signature color.

As the sun moves lower in the sky, its light must traverse a thicker atmosphere than when it is overhead, scattering more blue light while leaving only red and orange to reach us; this explains why sunrises and sunsets appear red or orange instead of having been completely blue when seen overhead.

Space may appear white because there’s no atmosphere to scatter sunlight rays, yet atmospheric particles still scatter them to some extent, though not nearly as strongly due to being larger than their wavelength. Even so, blueish-violet light waves still get scattered by particles within our atmosphere at different frequencies and this has less of an effect here.

Reasons behind why the sky appears multicolored are because atmospheric particles contain particles made up of all of the colors of the rainbow, including fine dust particles dominated by blue hues (for instance from forest fires or volcanic eruptions), yet most times blue and violet come to dominate (at least frequency space) creating what we perceive to be blue skies.

Blue light is scattered more

Answers lie within our planet’s atmosphere, where light waves that hit Earth’s atmosphere are bent back by microscopic particles and molecules, scattering light waves according to wavelength and length; shorter wavelengths like blue and violet tend to be scattered more than long ones like red or orange – thus giving the sky its color.

If you shine a beam of white light through clear fluid that contains microscopic particles (such as water or milk), its sidelight will appear blue-tinted due to shorter wavelengths being more likely to be scattered by particles than longer red wavelengths – this phenomenon explains why skies appear blue during daylight hours.

John Tyndall first described this phenomenon in 1869. He observed that light passing through liquid with nanoparticle suspension produced a blue tint similar to how polarized sunglasses make sunlight look deeper and more intense. Furthermore, the hue of the sky depended upon ratio between frequencies of various light-absorbing particles in suspension.

As we observe the sky, we see an array of all the colors that comprise visible light – all primary hues plus blue and red; our brains interpret this mixture as white.

At midday, blue component of sunlight scatters more widely than red or orange components; therefore, its appearance dominates skyscape during daylight hours on cloudless days; at sunset/sunrise time however, its color fades towards red as closer it gets to horizon.

At these times of day, sunlight must travel further through the atmosphere than at other times of the day; it has thus been scattered more widely away from its source; this leaves less red, yellow and orange wavelengths reaching our eyes, creating an appearance of muted reddish-orange colouring.

Blue light is polarized

The sky is blue due to air molecules — predominantly oxygen and nitrogen — scattering blue and violet light more than red light, an effect known as Rayleigh scattering which gives our skies their signature hue in daylight hours despite pure sunlight looking white without interference from atmosphere and clouds.

Violet and blue wavelengths are more susceptible to being absorbed by gases in the atmosphere, thus decreasing their chances of reaching Earth. As light passes through multiple layers, its wavelength length gradually lengthens until eventually it reaches your eye without much or any blue remaining, giving rise to what we perceive as red sunsets.

Why does the sky seem blue in the first place? The story begins in the ocean where blue-green microbes known as cyanobacteria invented photosynthesis as an energy conversion technique and revolutionized life on Earth. Photosynthesis converts sunlight and carbon dioxide into plant energy while producing oxygen as a byproduct – something the ocean was full of thanks to these blooming cyanobacteria colonies which, over time, released more and more of this airborne oxygen into Earth’s atmosphere and contributed to giving its characteristic hue.

At midday, when sunlight passes through only a very thin layer of atmosphere, blue parts of the spectrum tend to scatter more than red ones; so our daytime view appears predominantly blue. But at sunset when sunlight has traveled through more atmospheric layers, its mixture of blue and red wavelengths appears as dark blue light that seems almost black in appearance.

Ideally, our atmosphere would contain only gases with wavelengths comparable to light wavelengths that acted as Rayleigh scatterers and created blue skies. Unfortunately, there are other particles like dust and aerosol larger than wavelengths which scatter all colors more or less equally (known as Mie scattering) giving an appearance of milky white skies.

Red light is polarized

As sunlight passes through the atmosphere, its energy gets scattered in various directions by air and gas molecules. This scattering is strongest at the blue end of the spectrum and accounts for why skies look bluer; this phenomenon is known as Rayleigh scattering.

Blue and violet light wavelengths tend to get absorbed by atmospheric particles, while red and yellow wavelengths pass through and reach our eyes – leading us to perceive a sunset as more orange or pink than it would normally appear.

Lower in the sky, sunlight has to travel through more atmosphere before reaching us – this means more blue and violet light is scattered off into space, leaving behind longer red wavelengths – giving sunset its characteristic red hue.

Dust, pollution and water vapor in the atmosphere can have an enormous effect on the colors of the sky. Particles such as these cause it to appear hazy or cloudy and lessen its intensity; such effects have even been witnessed on other planets like Mars where sunset has an orange tint due to permanent atmospheric haze.

Polarization patterns vary throughout the day and year. At its lowest point (the zenith), when the sun is at its lowest point (Q = 1) it is fully horizontally polarized while at its highest point (the horizon) only partially so (U = -1).

Reasons behind why the sky appears both blue near the horizon and red closer to the Sun are: As one ascends in elevation, scattering decreases due to less atmospheric molecules above you scattering blue light more intensely while reds and greens absorb less of it and get their own colors as a result of its absorption; however, reds and greens still absorb some blue light, contributing their own hue to its spectrum of colors.

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