Unit Content
The History of the Sun and Our Solar System
Our middle-aged star in the cosmos is estimated to be only 4.6 billion years old.3,4 This bright incandescent light is powered by the conversion of hydrogen to helium through nuclear fusion, in regions where conditions reach a temperature of at least 15 million Kelvin, hot enough to fuse protons in the nucleus of atoms.5,6 The total energy emitted by the Sun is estimated to be 1034 Joules every year.7 Our medium yellow dwarf is thought to of formed from a nebula of dust and gas with some heavy metals which formed in previous generations of stars. The sheer magnitude of the Sun and its impact on the celestial bodies which accompany it cannot be understated. It provides the anchoring gravitational force(s) that govern the orbits of the revolving planets due to its massive size. In fact, the Sun represents 99.5% of all matter in our solar system which is equivalent to 330,000 Earths.8
The Sun’s birth directly coincides with the formations of the surrounding planets in our solar system. As the Sun coalesced from a cloud of gas, the central parts became the raging furnace we see today, the disk around formed the planets. The heat from the Sun caused the lighter materials to be swept away from the inner part of the disk leaving rocks and metals close to its center.9 This explains why our four terrestrial planets (i.e., Mercury, Venus, Earth and Mars) are located closest to the Sun and the four gas giants (i.e., Neptune, Uranus, Saturn, and Jupiter) are substantially farther away. The galactic turbulence of the past has given rise to our very existence which we revel in today.
The Sun’s Energy and Emissions
EMR and the Anatomy of the Sun
Figure 1. The main five main features of the Sun are shown above from a NASA publication titled “Mysteries of the Sun”.
Throughout our history every generation has woken up to the ball of gas suspended along the horizon emitting light and welcoming a new day. Observations of solar phenomena have allowed us to determine how light is emitted through the numerous layers amongst the turbulent sea of hydrogen and helium. Since the Sun consists of vast quantities of only a handful of elements the Sun’s anatomy is primarily governed by its mass and size, and the subsequent density and temperature differentials that exist internally.10 All light energy in our solar system is produced from the Sun’s core where temperatures reach 15 million Kelvin.11 These extreme conditions of high pressure, density, and heat force four hydrogen nuclei to fuse together, through a chain of reactions that begin with two protons fusing together, creating a single helium nucleus. The overall net mass of the helium nucleus is less than the initial combined masses of the hydrogen nuclei which subsequently cause a significant amount of energy to be emitted. This phenomenon was explained by Einstein when he postulated that energy is equivalent to the mass times the speed of light squared (E=mc2).12 This release of energy is in the form of highly energetic photons, which are bundles of electromagnetic energy, that travel through the Sun, pass-through the vacuum of space and eventually enter our atmosphere to provide bath us in the warm light needed for life. However, before the photons can reach Earth, they must pass through 300,000 km of highly dense plasma in the radiative zone.13 In fact, the plasma is so dense light only travels a few centimeters at a time before being scattered, absorb, or re-emitted by atoms along their journey.14 Once photons pass through the radiative zone, they enter the convection zone which serves as a buffer circulating hot gas towards the surface, as seen in Figure 1. As the gas expands it subsequently cools and sinks back down closer to the radiative zone to then be heated again. As the photons travel through the Sun their overall energy state lowers due to the chaotic nature of being scattered, absorbed, and reemitted along their journey.15 Scientists estimate that a single photon may take as much as 100,000 to 1,000,000 years to reach the surface of the Sun also known as the photosphere.16 However, once the photons reach the Sun’s surface it takes approximately 8 minutes to travel 150,000,000 km.17 The observable light we see from our Sun is the result of the countless energy transformations that start in the Sun’s core and eventually the Earth’s atmosphere. The light which we see today is a direct result of past proton-proton chains and a collection of photons slowly escaping the dense plasma within the inner layers of the Sun.
Properties Electromagnetic Waves
Our continued existence as a species remains dependent on the reliable energy emitted by the Sun. This energy arrives as electromagnetic radiation (EMR) which consists of an electric field and a magnetic field that are fixed perpendicularly to each other. These transverse waves travel through the vacuum of space at the speed of light (i.e., 300,000,000 m/s) through particles called photons.18 EMR are generated from the change of an electric or magnetic field as such these wave types interact with other charged particles, exerting a force upon them. This phenomenon can be seen in the polar regions of Earth with highly charged particles form the Sun interact with Earth’s magnetosphere to create dazzling auras. The energy state of a single photon determines the strength of the accompanying electromagnetic fields however the speed of a photon remains the same in the vacuum of space.19 The properties of an EM wave are described by its wavelength and frequency. A wavelength is defined as the distance between corresponding points of two consecutive waves like two throughs or two crests (see Figure 2). Whereas frequency is simply the number of waves that pass a fixed point per unit of time. The function of a wave is to carry energy. An EM wave carries energy from one point to another and its energy depends on its frequency, the higher the frequency that higher the energy.20
Figure 2. This diagram from the OpenStax Astronomy taken from chapter 5.1, illustrates a wavelength, in this case the distance between crest to crest, in a transverse wave.
The EM spectrum categorizes EM waves based on their wavelengths and frequencies which subsequently determine how they interact with matter of varying densities and charge. The classification schema falls on a logarithmic scale to denote the seven EM waves; these include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays (See Figure 3).21 EMR can have varying effects on life depending on its frequency. EMR with frequencies less than the visible spectrum are classified as non-ionizing as they lack sufficient energy to break molecular bonds to cause cellular damage.22
Figure 3. This illustration taken from Phillip Gringer, depicts the eight classifications of electromagnetic radiation along the spectrum along with the ranges in frequency and wavelength. The lower panel is a zoom of the part of the EM spectrum that is visible to the human eye.
EM Waves and Interactions with Visible Light Spectra
Most of the Sun’s light that reaches Earth is within the frequencies of infrared, visible, and ultraviolet.23 Through the interactions with Earth’s atmosphere EM waves are either reflected, scattered, absorbed, or refracted depending on several factors – composition (e.g., the ozone layer absorbs a lot of the UV radiation, water vapor absorbs infrared), density of matter, charge of particles, reflectivity of material, energy state of photons, and angle of incidence.24 These interactions are responsible for our everyday reality; from brushing your teeth in front of the mirror, to getting a sunburn on a hot summer day, to listening to music on the radio.
Figure 4. These diagrams illustrate the four primary wave interactions that occur when electromagnetic radiation interacts with matter. Images were taken and modified from NASA’s “Wave Behaviors” supplemental material.
Reflection
Reflections can occur in two forms, both regular and diffuse, under specific conditions between the angle of incidence of light spectra and the properties of the mirror or material.25 A reflecting surface often forms between the boundary of two different mediums (i.e., a gas interfacing with a liquid, or in the case of household mirrors, a solid interfacing with gas). A classic example is when you view your self-image on a placid lake, which appears to be reversed along the vertical axis.26 The sharpness of the image is a function of the angle of the Sun as well as the smoothness of the water. This occurs because the visible EM spectra of light (380 – 750 nm) are all being bounced back at a similar angle as they encounter the interface between air and water.27 Regular reflection can also take place along curved surfaces which cause images to become magnified or demagnified which is the foundational principle of how telescopes work.28 Diffuse reflection occurs on rough surface which cause the incident rays of light to bounce a different angle resulting in an obscure image. It should be noted that not all light is reflected perfectly on a lake, some of the electromagnetic energy is absorbed by the water itself and some is refracted depending on the refraction index of the material which explains why the image often appear dimmer and not as sharp.29
Refraction
Refraction is the change in direction of EMR as it passes through one medium to another.30 How much the EMR bends is determined by a material’s refractive index which often is a function of temperature and density. Several atmospheric phenomena (i.e., rainbows and mirages) can be explained by the refraction of visible spectra interacting with gas molecules or suspended water droplets. Rainbows form when visible light bends while interfacing with droplets of water in the sky. As rays of light cross the boundary between air and water they refract. Since white light is a composite of all visible spectra, each color varying in wavelength and frequency refract at slightly different angles resulting in the colors of the rainbow. The colors of a rainbow are determined by the wavelength of light and the numbers of times it is reflected inside a water droplet. In ideal conditions a primary and secondary rainbow can been seen after a thunder shower. When viewing a primary rainbow, the red appears at the top of the rainbow’s arch with violet at the bottom.31 A secondary rainbow results when visible light is re-reflect causing colors to faintly appear in the inverse order. The incoming rays of light travel to the edges of the water droplet and are reflected within the droplet until they cause yet another instance of refraction.32 The degree to which light bends is a function of the refractive index of the media and subsequently how much the medium is slowing down light.33 A droplet of saltwater has a slightly high refractive index of 1.33 to 1.5 which form rainbows with smaller a smaller radius compared to freshwater droplets.34 To determine the refractive index of a given material a ratio between the angles of incidence and refraction are compared following Snell’s law or the law of refraction.35 Snell’s law states that the ratio of the sine of the angles of incidence and transmission is equal to the ratio of the refractive index of the materials at the interface.
Scattering
Scattering with regards to EMR occur when interacting with a nonuniform surface or medium causing the trajectory of the incoming wave to deviate from a predicted path.36 Our own perceptions of color are largely governed by scattering as well as spectral absorption. Some of the most mesmerizing phenomenon occur during sunrise and sunset where clouds will take on a red hue especially if smoke particles from forest fires are suspended in the air due to specific type of scattering known as Raleigh Scattering. This type of scattering occurs when visible EMR collide with particles smaller than its wavelength.37 According to the Raleigh model the particle must be at least 1/10 the diameter of the wavelength interacting with it.38 Let us examine a typical sunny day, as the Sun’s visible light passes through Earth’s atmosphere some of the photons are scattered when they interact with molecules such as oxygen (diameter of 300 picometers) and nitrogen (diameter of 252 picometers) of gas.39 As shown in Figure 2, visible light ranges from 380 nm to 750 nm and is comprised of red, orange, yellow, blue, green, and violet spectra. The diameter of a typical particle of dust can get as large a 10 nm which is substantially larger than the molecules of gas.40 As longer wavelengths of light (i.e., red and orange) pass through the earth’s atmosphere they have less of a chance being scatter amongst the gas a molecule compared to the shorter wavelengths of light (i.e., blue and violet). This is precisely why the sky appears blue rather than red on a typical sunny day, more of the blue wavelength is being scattered compared to the red wavelengths. However, during sunsets, the visible light passing through our atmosphere is at a shallow angle causing the visible light to travel through more of Earth’s atmosphere. Since the blue light is easily scattered away, the red wavelengths become more visible during this time of day.
Absorption
Absorption occurs in two types either by a charged free particle absorbing the EMR to a higher energy state or when the energy from the EMR is so great it causes electrons to be set free from an atom, also known as ionization.41 When EMR bombards matter it provides additional kinetic energy which manifests as heat. Why do some objects appear to have different colors? The colors of our clothes, cars, and shoes are a function of light being reflected and absorbed at different wavelengths of visible light. A blue shirt will appear blue as all colors with exception to the blue wavelength of light is being absorbed. Objects that absorb light often transform the energy into heat.42 If you have ever walked on a black sanding beach or a white sandy beach, there is a considerable difference in the experience. The elements that form black sandy beaches are such that they absorb all visible wavelengths generating an abundance of thermal emissions while the white sandy beaches reflect most of the visible light. Absorption can lead to deleterious effects on life through ionization. When sufficient EMR is applied to an atom an electron can become liberated from all its orbitals resulting in a positive ion.43 This process creates a charge differential between neighboring atoms and molecules that is hostile to DNA often leading to mutations or cancer.44 The extreme range of ultra-violet light can have this affect which is why sunburns occur during the peak of the day on sandy beaches. The EMR absorbed by your skin results in thermal emission causing your skin to burn by applying sunscreen you prevent the absorption of UV light and negate absorption at this frequency.
EM Theorical Discoveries
The modern technological era owes its prominence to the discovery of electromagnetism and electricity. The earliest documentation of electricity dates to 600 BCE from an ancient Greek philosopher and mathematician who described the phenomenon associated with rubbing animal fur on a variety of materials including amber.45 It took a thousand years for mankind to have a rudimentary understanding the relationship between electricity and magnetism. During the late 1700’s and early 1800’s considerable progress was made with respect to magnetic fields and voltaic electricity.46 In 1821 French physicist Andre Ampere discovered that electrical current produced an electrical force giving rise to his theory in electrodynamics.47 Initially physicist and scientists believed that electricity and magnetism were two phenomena independent from each other. In 1831 Michael Faraday investigated the effect electric fields had on magnets which established the concept of electromagnetic fields.48 James Maxwell further expanded upon the idea of electromagnetic fields by applying mathematics in 1873 which forms the basis for modern electromagnetic theory.49 These iterative and refinement of scientific principles spurred a booming technological revolution which began with the Industrial Revolution in the 18th century and continue to this day.
EM Spectra and Cell Phones
The prolific access to cellular devices has completely revolutionized communication. In an instant we can check in with family and friends across the globe. This has had a profound affect in the economy of developing countries and transformed popular culture. Students’ usage is typically confined to social media or texting. Further examination of the electrical engineering and the utilization of electromagnetic spectra may elicit greater appreciation for the technical marvel at their fingertips. This investigation will serve as a platform for critical thinking in the application of EMR interactions and the properties of EM waves.
Telecommunication
A cell phone is a two-way communication device that receives and sends radio signals at various frequencies.50 This can come in the form of directly speaking to a friend during a phone call or sending a message via a text. When you speak into a cell phone a microphone turns your voice into a set of electric signals. A microchip in the phone modulates radio waves to carry the electric signal over vast distances through a network of towers owned by your service provider.51 To prevent multiple carriers from broadcasting at the same frequency the Federal Communication Commission auctions off bandwidth every year to the highest bidder.52 These licensed frequencies are what the radio waves are transmitted along via the antenna in your phone. A person receives the electric signal from to these networks of towers which is subsequently modulated yet again to produce a sound wave. The speaker in your phone contains an electromagnet and permanent magnet that vibrates a diaphragm made of flexible material to create sound waves. 53 The frequency of the vibrations determines the overall pitch generated from the speaker. Cellphones transmit radio waves in all directions, in fact while on the phone with your friend over half of the emitted energy from your cellular device is absorbed by your head or body.54 However, since the EMR used in the transmission process is within the non-ionization portion of the EM spectrum few if any health sided effects result.
Touch Screen
Most of the electrical energy generated by the battery is used to provide ambient light to view content on screen. The display screen of a typical smartphone is made of three components, a liquid crystal display, a tiny grid of electromagnetically generating wires, and protective glass.55 The liquid crystal display uses an electric current and a backlight to adjust the color of each pixel on your screen. When a fingertip or stylus applies pressure on the screen several thin resistive layers send a localized electrical signal thus detecting the position and magnitude of pressure being exerted.56 There have been similar models that utilize infrared frequencies to yield a similar result.
Camera
As the evolution of cellphone and smart devices has progressed so too have their camera features which is a marketing strategy for every generation of cellular device. The camera on a cellphone operates like traditional digital single-lens reflex cameras with some key differences. Since the lens on a smartphone are relatively small an image is capture using a series of convex and concave lenses that work to focus visible light towards a sensor thus creating a digital image.57 Most cellphones sold today come with multiple cameras with lenses of varying focal lengths which allows users to capture wider angles-of-view or magnify the image depending on settings. Once the visible light interfaces with the system of lenses the EMR is refracted at varying angles which pass through a sensor. Most mobile devices utilize a Complementary Metal-Oxide semiconductor (CMOS) to digitize EMR as its extremely energy efficient.58 This sensor is made up of millions of light-catching cavities called photosites.59 The strength of the digital signal is dependent on exposure length and shutter speed. A gray scale composite image is formed from this process. The photosite will result as white with a large exposure of light and black with low exposure to EMR.60 An additional filter is needed for the sensor to interpret color. Most commonly digital cameras use a Bayer filter which consists of an array of red, green, and blue filters which captures light only within those bandwidths.61 Once the photosites relay the composite information of RGB a post processing calculates the color values for neighboring pixels resulting in a digital image.62 This complex sequence of events occurs every time your students take a selfie. The rapid advancement of digital technology is thanks to the fundamental understanding of electromagnetism and the constant source of electromagnetic radiation from the Sun. I truly hope we can appreciate the marvels of science by simply reflecting on the marvels of taking a digital photo with our classes.
Figure 5. This illustration from commons media shows the Bayer filter array which allows color values to be associated with pixels when taking photos on a cellular device.
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