During sunrise and sunset, people may witness a blanket of different colors that intricately blend with each other to fill the sky. But why exactly is the sky this colorful during these times of the day?
Blue Sky During the Day
To get to the bottom of this, it is first crucial to understand why the sky stays blue throughout the day.
The mechanism responsible for this is a kind of light scattering known as Rayleigh scattering. The phenomena was named after Lord John Rayleigh, who was the one to describe it first during the 1870s.
Cody Braud, a FOX Weather meteorologist, says that there are various kinds of scattering. However, the domination of Rayleigh scattering covers the majority of daytime. It mainly depends on sunlight wavelength.
The Rayleigh scattering equation is proportional to the wavelength's inverse. A wavelength that is shorter would boost dispersion as air molecules first absorb sunlight. Scattering then follows.
Braud says that blue has the wavelength that is shortest in the spectrum scale that is visible. In the day, the Sun is nearest to the surface of the Earth regardless of where a person is all over the planet. With this, light scattering will be at its maximum, offering vibrant blue tones.
ALSO READ : Is the Sky Blue? Nature of Light, Molecules and Quirky Atmosphere Reveal Why It Has More Than One Color
Colors of Sunrise and Sunset
When the sun begins to set, the opposite takes place. During this time, the visible light wavelength goes up. Braud explains that this makes sense as the sun goes further away.
Though the wavelength of the color red is longer compared to that of blue, more red light gets scattered as the Sun moves further away from the Earth.
While some clouds do not add to the vibrance of colors, air particles and dust do. Larger pollution amounts in the atmosphere boost the amount of particle scattering.
There are also other weather phenomena, such as volcanic chemicals, wildfire smoke, and Saharan dust, that could increase particles that are available in the atmosphere. Like pollutants, the particle increase could offer increased scattering changes, resulting in sunsets and sunrises that are more vivid.
Braud explains that when aerosol is compared with air molecules, the aerosol has an irregular and much larger shape. This leads to a novel scattering type known as Mie scattering.
Gustav Mie, a German physicist, found out that such a type of scattering could boost colors. Rather than having an equal scatter in every direction, Mie scattering will be at its greatest in the direction where the visible light comes from.
Braud explains that as the sun sets and hits every aerosol, the light ends up scattering the most in its traveling direction. This leads to colors that are very vibrant.
Moreover, due to how the color red has the longest wavelength of light that is visible, the sun appears red at the horizon. This is where its long path across the atmosphere ends up blocking other colors.
Check out more news and information on Environment & Climate in Science Times.
