Science of the Stars

 Science of the Stars

Casie Thibeault

SCI 151

August 10,2015

Sushruth Mehta

 Science of the Stars

        In this paper we will be discussing the science of the stars. I will talk about how astronomers determine the composition, temperature, speed, and rotation rate of distant objects. I will briefly explain the properties of stars in "What is a Hertzsprung-Russell diagram?" section in Ch. 11 of the textbook “The Essential Cosmic Perspective” and I will also describe the lifecycle of the Sun and determine where the Sun is in its lifecycle.

Studying Distant Objects

        Astronomers study light that comes from distant objects to determine its composition, temperature, speed, and rotation of distant objects. This process of determining its composition is called spectroscopy. Spectroscopy was first used to study celestial objects in 1863 by William Higgins. By using this process Higgins discovered that the Sun and most stars are primarily composed of hydrogen gases. By using spectroscopy it was also noted that different objects give off different spectrums of light and absorb different spectrums of light. Where an object falls in the spectrum of light can be determined by examining its peak intensity at each wave length of light. The spectrum is the band of colors that white light is composed of, in the order: red, orange, yellow, green, blue, indigo, violet from long to short wavelength. The light helps us to determine an objects composition, temperature, and rotation as well (Col, 2015).

        There are three types of spectra used to evaluate light. The absorption spectrum  is when objects  absorb light at different wavelengths.. The intensity of this kids of light drops in objects which absorb light and appear as the darker lines on a rainbow of colors. Stars and planets that have atmospheres, and galaxies absorb light and are put into the absorption spectra. (Col, 2015).

        Another type of spectrum that gives off light at different wavelengths is called the Emission spectrum. The atoms and molecules in hot gases create extra light and produce bright lines up against a black background. Comets, nebula and some types of stars fall in these spectra called the Emission spectrum or bright line spectrum (Col, 2015).

        Objects whose light gives off a rainbow of colors like a prism without interruption fall in the spectrum called the Continuous spectrum. One measures a star’s brightness based  off of  its luminosity and its distance from us. This measurement is done by using Inverse Square Law for Light. In other words, the farther away you are from an object the less light will appear.

Hertzsprung-Russell Diagram

        Astronomer Ejnar Hertzsprung and astronomer Henry Noris Russell noticed the relationship of the stars surface temperature and its luminosity. They used this relationship to develop a type of graph to identify where each star is in its lifecycle. The graph is essentially based on two properties of the stars. One property is the star’s surface temperature, also known as its spectral type. The surface temperature is plotted on the x-axis or horizontally. Red stars have the hottest temperature where as blue stars have a cooler temperature. We are able to tell a star’s surface temperature by examining the wavelength of its peak intensity. This is known as  Wien's law. Wien's Law tells us that objects of different temperature emit spectra that peak at different wavelengths (Cornell.edu, 2015). The second property of the star graphed on the Hertzsprung-Russell diagram is the star’s luminosity or amount of energy radiating from it. This property is plotted on the y-axis and is usually based on a ratio-scale with the main reference point being the Sun. By graphing these two properties we are able to map out where most stars are in their lifecycle at  that point in time.