Science of Sunlight and Stars
SCI/151
May 16, 2011
Troy Mazely

Science of Sunlight and Stars
Light is used in many ways, and is a form of energy that can be created, travel through space, and be absorbed. Light can react as a particle, because it sends all its energy to one place. A particle of light is called a photon. Photons can be absorbed into objects, bounce off objects, or fly through space. Over the course of a million years, clumps of particles will grow into what is called a “protostar” and draw in more gases and grow even hotter. This is how stars are formed and is a point in a star’s life.
Astronomers determine composition, temperature, speed, and rotation rate of distant objects with a tool called a spectroscopy. When a star gives off light and the light splits by prism, the spectral pattern reflects a star’s composition. All stars are 95% hydrogen, so the variations in composition expose its age, luminosity, and origin. Composition of ages can be determined by observing the light of a star. The temperature of a star can be determined from its color and its spectrum. All stars have different colors because of its light radiation. Another way to determine the temperature of a star is to examine the spectral lines in the starlight. “Because we sometimes describe light as an electromagnetic wave, the complete spectrum of light is usually called the electromagnetic spectrum” (Bennett, Donahue, Schneider, and Voit, 2009). This is used to explain all types of electromagnetic energy that exist throughout the universe. Spectra consist of three different types: continuous, emission line, and absorption. Emission and absorption lines tells us that each type of atom, ion, or molecules obtain a rare set of energy levels. Every atom has its own rare spectral fingerprint because it has its own rare set of energy levels. If matter is made of hydrogen, it shines and absorbs light at specific wavelengths and makes it possible to detect its presence in distant objects. Electromagnetic waves are organized in the electromagnetic spectrum according to their wavelength from the shortest, which are known as gamma rays to the longest that are known as radio waves. Electromagnetic energy is created by vibration. It produces waves that carry energy. Each magnetic wave shines a different level of energy. These energies travel soundlessly at the speed of light and produce a signature wave with a rare range of length, energy and frequency that astronomers can identify and measure. Wave length and frequency are vice-versa related, meaning that the greater the length of the wave, the lower its frequency will be.
The H-R diagram (Hertzsprung - Russell diagram) is a tool to aid the understanding of the stellar evolution. Each star is represented by a dot. The position of each dot on the diagram tells one two things about each star: its luminosity (or absolute magnitude) and its temperature. The vertical axis represents the star’s luminosity, which is the amount of energy a star radiates in one second, meaning how bright or dim the star appears. The horizontal axis represents the star’s surface temperature, just the surface not the inside of it, labeled using the Kelvin temperature scale. The higher (hotter) temperatures are on the left, and the lower (cooler) temperatures one on the right. Reading an H-R diagram: a star in the upper left corner of the diagram would be hot and bright. A star in the upper right corner would be cool and bright. “The sun rests approximately in the middle of the diagram and it is the star which we use for comparison” (star life cycle 2003-10). A star in the lower left corner of the diagram would be hot and dim. A star in the lower right corner would be cold and dim.
The sun is the central point of our solar system and the largest star that we rely on for our survival and makes more than 90% of the solar systems mass. The sun is made up of six parts. The six parts starting from the inside out are: the core, the radiation zone, the convection zone, the photosphere, the chromosphere, and the corona. The core, reaches temperatures of 15 million Kelvin, hydrogen atoms are converted into helium through thermonuclear fusion. The pushes pressure out, while the gravity balances the force by pulling it back in. The photons from the nuclear reactions are taken in and released into the radiation zone. The currents of the gas are circulated and converted to the surface in the convection zone. The photosphere, brings 99% of the visible light, is the surface of the sun. The photosphere is about three hundred miles thick, with temperatures reaching five thousand eight hundred Kelvin. There can be side darkening visible in this layer, which can happen when the edge appears darker due to light being shined from higher, cooler regions, creating a possible shadow. The chromosphere reaches a few thousand miles above the surface and can vary in temperature from six thousand Celsius to fifty thousand Celsius. “It appears red because hydrogen atoms are in an excite state and emit radiation near the red part of the visible spectrum” (Enchanted learning, 2006). The outside part of the sun is the corona. The corona stretch millions of miles from the solar surface with temperature of two million Kelvin, which is hot enough to beam x-rays. The coronal layer also beams threatening waves. There are some scientists who are presently working out ways to study these layers.
The sun was formed about 4.57 billion years ago when the rapid collapse of hydrogen molecular cloud led to the formation of a third generation, the sun. Solar formation is dated in two ways: the sun’s current main sequence age, determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about the same amount of years the sun was formed. The sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than four million tons of matter is converted into energy within the sun’s core, producing neutrinos and solar radiation; at this rate, the sun will have converted around one hundred Earth-masses of matter into energy. The sun will spend a total of about ten billion years as a main sequence star.
Reference:

Bennett, J., Donahue, M., Schneider, N., & Voit, M. (2009). The cosmic perspective (5th ed.). San Francisco, CA: Pearson/Addison Wesley.
Taylor, R.j. (1994): The Stars: Their Structure and Evolution (2nd ed.). www.astro.unl.edu www.cosmic-ray.org www.universetoday.com www.enchantedlearning.com