The sun emits radiation across a wide range of wavelengths, with the majority of its energy falling within a narrow bandwidth. The percentage of solar radiation emitted at different wavelengths is:
Ultraviolet (UV)
About 7% of the sun's radiation is in the UV range, from 100–400 nanometers (nm).
Visible light
About 42–43% of the sun's radiation is in the visible light range, from 380–780 nm.
Near infrared (NIR)
About 52–55% of the sun's radiation is in the NIR range, from greater than 780 nm.
Infrared
About 49% of the sun's radiation is in the infrared range, from 700 nm–1 mm.
X-rays, gamma rays, and radio waves
Less than 1% of the sun's radiation is emitted as these types of radiation.
The ozone layer absorbs most of the sun's UV radiation, protecting Earth. The hole in the ozone layer over the Antarctic allows more UV radiation to reach the Earth, which can be harmful to habitats.
*The sun emits all colors of visible light*, and, *in fact, emits all frequencies of electromagnetic waves*. This includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays.
The sun emits all of the colors of the visible spectrum because it is a hot thermal body that emits light through the process of thermal radiation.
*Why is the sun yellow color ?*
It may be tempting to examine the color content of sunlight and identify the brightest color (the peak frequency) as the actual color of the sun.
The sun's actual color is white, but it appears to have different colors due to the Earth's atmosphere:
White light
The sun emits light across the entire visible spectrum of colors, from red to violet, in roughly equal amounts. This combination is perceived as white light.
Scattering
The Earth's atmosphere scatters blue light more than red light, which makes the sun appear yellow. This phenomenon is called *Rayleigh scattering*.
Sun position
The sun appears white at noon because it's directly overhead, so its light has less air to travel through and less scattering from dust and other particles.
Sunrises and sunsets
During sunrises and sunsets, the sun's light passes through more atmosphere, causing even more blue light to scatter. This means that the sun's spectrum has a greater percentage of red light during these times.
Close examination of the visible-light spectrum from our Sun.
Patterns are also evident in a graph of an object's reflectance. Elements, molecules, and even cell structures have unique signatures of reflectance.
A graph of an object's reflectance across a spectrum is called a spectral signature.
Spectral signatures of different Earth features within the visible light spectrum ARE shown below.
*This is how light interacts with atoms*
https://dept.harpercollege.edu/chemistry/chm/100/dgodambe/thedisk/spec/5back4.htm
*Absorption* and *Emission*
An atom changes from a ground state to an excited state by taking on energy from its surroundings in a process called absorption.
The electron absorbs the energy and jumps to a higher energy level.
In the reverse process, emission, the electron returns to the ground state by releasing the extra energy it absorbed.
The test tube in the figure contains an orange solution. The solar spectra is white light. When sunlight shines through an orange solution, the violet, blue and green *wavelengths are absorbed*. The other colors pass through. The transmitted light or reflected is the light we see, and *it looks orange.*
When sunlight is shined on a green leaf, the violet, red and orange wavelengths are absorbed. The reflected wavelengths appear green. ( Second image above mentioned )
*Why black and white in light ?*
Black and white objects are just the extremes of colored objects. Black objects absorb all the light shined on them. There is no reflected light, so we see black (the absence of color). If all of the light is reflected, we see all the wavelengths, which means we see white light
Then you may ask.. what aboUt other colors happens 🤔
*Why do objects emit complementary colors?*
The excited electrons absorb certain wavelengths of light. What humans see is the complementary color of the absorbed wavelengths,
i.e., the remaining wavelengths of light that are not absorbed. For example, if an object absorbs the red wavelengths of light, we will perceive it as green (red's complementary color).
*Complementary colors* are *pairs of colors* which, when combined or mixed, cancel each other out (lose hue) by producing a grayscale color like white or black. When placed next to each other, they create the strongest contrast for those two colors. Complementary colors may also be called "opposite colors".
*Ok simple question:*
Why does the pink color happen in the sun's refection of an object?
*Notice*: that we also don't see pink as a color on the visible light spectrum.
This is because pink is also a mixture of colors. *We see pink when both red and violet light are reflected.*
When we see color, we see the wavelength of light reflected, or not absorbed, by the object.
https://dept.harpercollege.edu/chemistry/chm/100/dgodambe/thedisk/spec/complem.htm
Thermal radiation happens because excited state electrons jump ground states and emit thermal energy.
*Is molecules radiating or reflecting the colors ?*
*In a general sense :*
Molecules reflect light to create color, but molecules themselves do not have color:
Reflection
The electrons on the outside of an atom or molecule absorb light and then emit some of it back. The color we see is determined by the wavelengths of light that are reflected. For example, an apple appears red because its surface reflects red wavelengths and absorbs the rest.
*Deep sense:*
Light reflects off molecules when the light waves' frequencies don't match the natural vibration frequencies of the molecules' atoms.
When this happens, the electrons in the atoms vibrate briefly, then re-emit the energy as a reflected light wave
Here are some other things to know about light and molecules:
*Light absorption*
When light waves' frequencies match the energy levels of the electrons in a material, the electrons absorb the light's energy and change their energy state. The energy can be re-emitted as a photon, or it can be retained by the material, which heats up.
*Light scattering*
Light scatters in all directions when it hits small particles, like gas molecules, or larger particles, like dust or water droplets. The amount of scattering depends on the size of the particle compared to the wavelength of light.
*Chromophores*
Chromophores are regions in molecules where the energy difference between two molecular orbitals is within the visible spectrum. When light hits a chromophore, an electron can be excited from its ground state to an excited state.
*Angle of incidence and reflection*
When light reflects off a surface, the angle at which it comes in (the angle of incidence) always equals the angle at which it reflects.
*Visible Light Reflection and Transmission*
Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural frequencies of vibration of the objects. When light waves of these frequencies strike an object, the electrons in the atoms of the object begin vibrating. But instead of vibrating in resonance at a large amplitude, the electrons vibrate for brief periods of time with small amplitudes of vibration; then the energy is reemitted as a light wave.
If the object is transparent, then the vibrations of the electrons are passed on to neighboring atoms through the bulk of the material and reemitted on the opposite side of the object. Such frequencies of light waves are said to be transmitted. If the object is opaque, then the vibrations of the electrons are not passed from atom to atom through the bulk of the material. Rather the electrons of atoms on the material's surface vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of light are said to be reflected.