Science of the Stars Essay

        Stars, to the naked eye are just twinkling dots in the night sky providing a picture of awe inspiring beauty, but in reality they are more than just that.  Astronomers have been able to determine the composition, temperature, speed, and rotation rate of these distant space objects.  Using the H-R diagram these properties that make up the stars can be explained to anyone that is not a scientist.  Astronomers have also used these tools to determine the lifecycle of the Sun and just where it is in the lifecycle.  Understanding the stars can help astronomers better understand the beginning of the Universe, as well as help us understand our own large star the Sun.

        Astronomers use a process called spectroscopy, which studies the light of distant objects such as stars, to determine their compositions, temperatures, speeds, and rotations.  It was discovered that different objects give off and absorb different spectrums of light, and spectroscopy uses that information to determine the properties of object in space.  William Higgins, an English astronomer in the 1800s, first used to spectroscopy in 1863 to study celestial objects. This process helped him discover that the primary composition of the Sun and most stars was hydrogen gas.  An object’s peak intensity at each wave length of light helps to determine its position on the light spectrum.  The objects determine position on the light spectrum leads to a determination of its composition, temperature, and rotation.  Absorption spectrum, emission spectrum, and continuous spectrum, are the three different types of spectra used to evaluate the light given off by the objects in space.  Objects, such as stars, planets, and galaxies, fall in the absorption spectrum because these objects absorb light and appear as dark lines on a rainbow of colors (Kulesa, 2000).  Objects like comets, nebula, and certain types of stars, due to the atoms and molecules found in the hot gases that they are composed of fall in the emission spectrum because they give off light at different wavelengths and produce bright lines on a black background (Kulesa, 2000).   Objects that fall into the continuous spectrum give off a rainbow of colors without interruption.  Spectroscopy has been an important tool in helping astronomers determine the physical properties of the objects found in outer space, and helping us better understand the universe around us.  

        By utilizing a technique called the Inverse Square Law of Light a stars distance can be inferred by whether or not it is dimmer or brighter than other stars around it.  This is because a stars luminosity and distance from Earth is what makes it dimmer or brighter than other stars.  A Danish astronomer by the name of Ejnar Hertzsprung and an American astronomer by the name of Henry Noris Russell identified the relationship of the star’s surface temperature and its luminosity, and they used the identified relationship to develop a type of graph called the H-R Diagram to identify where a star is in its lifecycle.  The graph uses two different properties, a stars surface temperature, and its luminosity, to infer the star’s stellar properties.  The surface temperature of the star is plotted on the x-axis. Examining the wavelength of a star’s peak intensity, astronomers are able to determine its temperature in order to plot the star correctly in the graph. Stars that give off a blue tint are known to be hotter, while white tinted stars are cooler, and red tinted stars are the coolest.  The luminosity, the amount of energy radiating from the star, is plotted on the y-axis of the graph. Luminosity is determined “either as a ratio compared to that of the Sun or as absolute magnitude” (Australia Telescope National Facility, n.d.).  On this graph it is seen that stars fall into three group’s white dwarfs, main sequence stars, and super giants. The majority of stars including the Sun fall into the main sequence, and “vary widely in effective temperature, but the hotter they are, the more luminous they are, hence the main sequence tends to follow a band going from the bottom right of the diagram to the top left” (Australia Telescope National Facility, n.d.).  The giants and super giants fall in the top right corner of the graph, and are luminous stars that have evolved off the main sequence. The white dwarves are found in the lower left corner of the graph, are hotter than the other stars as well as have a smaller radius.  Plotting the surface temperature and luminosity of stars has helped astronomers greatly in determining a stars lifecycle as well as its other properties.