Geo Chp.28 Notes for Website NEW 2017-2018.doc - 28.1 A...

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28.1- A Closer Look at Light (p.612-616) *Astronomers analyze light from objects in space in order to learn about the composition and movement of the objects. After today’s lecture, you should be able to : - Describe the characteristics of electromagnetic radiation . - Explain ways of analyzing light in order to get information about stars. - Explain the Doppler Effect and how it gives information about the motion of stars. *Light is a form of electromagnetic radiation, which is energy that travels in waves. The Electromagnetic Spectrum of Radiation *There are several different forms of radiation . -These are arranged on a spectrum by the size of their wavelengths , from longest to shortest -A wavelength is the distance from 1 wave crest to the next wave crest. Types of Radiation (from longest to shortest) (p.613) Radio Waves = longest waves *least energy (1000-1 m) Microwaves (10 -1 – 10 -4 m) Infrared (Heat ) (10 -4 – 10 -6.5 m) Visible Light = ROYGBIV → Red (longest) to Blue (shortest) (10 -6.5 – 10 -7 m) Ultraviolet (10 -7 – 10 -8 m) X-Rays (10 -8 – 10 -11 m) Gamma Rays = shortest waves * most energy (10 -11 m and smaller) *All of these travel at the speed of light ! The Spectroscope *White light = All colors of visible light Can be broken down into the visible spectrum using a spectroscope - a tool which uses a prism to separate light into its different colors! o ROYGBIV = red, orange, yellow, green, blue, indigo, violet o Spectrum can be used by astronomers to learn more about distant stars ! Spectroscopes break light into 3 types of spectra: Types of Visible Spectra (p.614) 1) Continuous Spectrum Shows an unbroken band of the colors of the visible spectrum Indicates that its source is emitting light of all visible wavelengths. Source is a form of glowing solid, liquid, or compressed gas o Examples: hot filament of an electric light; molten iron; compressed gas inside stars 2) Emission Spectrum Shows a series of unevenly spaced lines of different colors & brightnesses Indicates that the source is only emitting light of certain wavelengths . Used to identify elements found in the source object, since: wavelength
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o Each element has its own unique emission spectrum! Like a fingerprint! 3) Absorption Spectrum Shows a continuous spectrum crossed by dark lines. o This forms when light from a glowing object passes through a cooler gas - (Like that of its atmosphere or outer layers.) o The lines represent the composition of the gas (or the star’s outer layers!) Comparing emission and absorption spectra, scientists can determine what elements are present in the cooler gas . The SUN as an Example: Interior = hot , compressed gases = continuous spectrum Outer Layers = chromosphere & photosphere o These are cooler than the interior.
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