Chapter 4

4.1 Spectral Lines NO radiation emits a perfect blackbody spectrum All spectra deviate from this ideal by a lot or just a very small amount These deviations tell us the about the physical conditions

4.1 Spectral Lines Spectroscope- a device used to analyze radiation Consists of an opaque barrier with a slit, a prism, and an eyepiece

4.1 Spectral Lines Continuous spectra- spectrum in which the radiation is distributed over all frequencies Example: the black body radiation emitted by a hot dense body

Emission Lines- narrow “slices” of the continuous spectrum 4.1 Spectral Lines

4.1 Spectral Lines Absorption lines- dark lines that interrupt a continuous spectrum- representing wavelengths “absorbed” by gases present in the outer layers of the sun, or Earth’s atmosphere Now referred to as “Fraunhofer Lines”

spectroscopy- the analysis of the ways in which matter emits and absorbs radiation 4.1 Spectral Lines

4.1 Spectral Lines Kirchhoff’s Laws: A luminous solid or liquid, or a sufficiently dense gas, emit light of all wavelengths and so produces a continuous spectrum of radiation A low-density hot gas emits light whose spectrum consists of a series of bright emission lines. These lines are characteristic of the chemical composition of the gas A cool, thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place

4.2 The Formation of Spectral Lines Bohr Model

4.2 The Formation of Spectral Lines Photons- a particle of electromagnetic radiation

4.3 Molecules Molecule- tightly bound group of atoms held together by interactions among their orbiting electrons

4.4 Spectral Line Analysis Spectrographs are attached to telescopes and galactic clouds and stellar dust replace the atmosphere in intervening with the spectral lines

4.4 Spectral Line Analysis Spectral lines seen from looking at stars are compared to laboratory spectra of known atoms, ions, and molecules to determine the chemical composition of the star