Spectroscopy Lecture

Standards Explain how objects in the universe emit different electromagnetic radiation and how this information is used Describe how waves are used for practical purposes (e.g., Doppler effect) Understand how knowledge about the universe comes from evidence collected from advanced technology (e.g., telescopes)

Spectroscopy How do we know what objects out in space are made out of without directly examining them? Spectroscopy – is the way in which astronomers can determine the chemical composition of objects such as stars and planets This is done by observing the object’s spectrum (plural, spectra)

Spectroscopy Spectroscopy is the study of how atoms absorb and emit electromagnetic radiation This happens when electrons move to different energy levels within an atom.

Spectroscopy Absorption – an electron gains energy from an incoming photon and it jumps to a higher energy level. Emission – occurs when the electron returns to a lower energy level and gives off (emits) a photon (light).

Spectroscopy Spectroscope – instrument used to determine the composition, temperature and speed of objects. Spectroscopes that are used to observe objects in space are made of a prism combined with a telescope

Types of Spectra There are 3 types of spectra: Continuous spectrum Emission spectrum Absorption spectrum

Continuous Spectrum Unbroken band of colors Ex: Rainbow Comes from 3 sources: Glowing (hot) solid Glowing liquid Hot, compressed gases deep inside a star

Emission or Bright Line Spectrum Spaced series of lines of different colors and brightness Comes from a glowing, thin gas or vapor Ex: neon gas Each element has a unique bright line spectrum This is like the element’s fingerprint, and allows us to identify it in distant objects!

Emission Spectra Photo: http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap04/FG04_03.jpg

Absorption or Dark Line Spectrum Series of dark lines within a continuous spectrum Occur where light is absorbed Dark lines are in same places as bright lines for a particular element Form when source passes through a cool gas

Absorption Spectra Photo: http://www.tam.gov.tw/ vtam/EN/show.asp?XH16

Absorption or Dark Line Spectrum The sun’s spectrum is an absorption spectrum: Hot, compressed gases in sun’s center radiate a continuous spectrum Gases pass through outer, cooler layers and are absorbed The sun’s spectrum has 1000’s of dark lines 67 elements have been identified on the sun

Solar Spectrum

Absorption or Dark Line Spectrum Absorption spectra are used to determine the composition of planets’ atmospheres Planets shine by reflecting light from the sun If spectrum shows dark lines that are not part of sun’s spectrum, then they are caused by substances in the planet’s atmosphere

Doppler Effect in Spectra Doppler effect – a motion-induced change in observed wavelength (car ex.)

Doppler Effect in Spectra Dark lines in stars’ spectra are shifted slightly right (towards blue) or left (towards red) of the bright line spectrum of the element

Doppler Effect in Spectra Red shift – if shifted toward the red end, means longer wavelengths coming from star and star is moving away Blue shift – if shifted toward the blue end, means shorter wavelengths coming from star and star is moving toward us