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current understanding of nature of light emerged


showed that light sometimes behaves as particles and sometimes as waves

wave model

wavelengths of radiation vary

white light

consists of several wavelengths corresponding to the colors of the rainbow

particle model

exert a pressure called radiation pressure on matter



particle model

shorter wavelengths correspond to more energetic photons

light comes from

movement of electrons in atoms


contains protons and neutrons


atoms with the same number of protons


atoms with varying numbers of neutrons


atoms with varying numbers of electrons

spectral lines

when electron jumps form one energy level to another

186,000 m/s

speed of light

visible light

only one small part of an array of energy

electromagnetic radiation

gamma rays, x-rays, UV light, visible light, infrared light, radio waves

visible light

only one type of electromagnetic radiation emitted by stars

each type of EM radiation

travels at exactly the same speed (speed of light)

peak color (wavelength)

shifts to shorter wavelengths as an object is heated


inversely proportional to temperature


emits all colors


most intensely emits blue-green part of spectrum


learned by analyzing starlight

chemical composition

learn by analyzing starlight


study of properties of light that depend on wavelength


light pattern produced by passing light through a prism which spreads out the various wavelengths

continuous spectrum

produced by an incandescent solid, liquid, or high pressure gas

continuous spectrum

uninterrupted band of color

dark-line (absorption) spectrum

produced when light is passed through a comparatively cool, low pressure gas

dark-line (absorption) spectrum

appears as a continuous spectrum but with dark lines running through it

bright-light (emission) spectrum

produced by a hot (incandescent) gas under low pressure

bright-light (emission) spectrum

appears as a series of bright lines of particular wavelengths depending on the gas that produced them

dark-line (absorption) spectrum

most stars have


instrument used to spread out the light

emission and absorption spectra

allow astronomers to determine the elements present in a distant star

each chemical element

produces its own unique set of spectral lines when it burns

brightness of spectral lines

depend on conditions in spectrum's source

continuous spectrum

produced by a hot,dense gas or object - is a complete rainbow of colors without any specific spectral lines

emission line spectrum

produced by hot, rarefied gas - series of bright spectral lines against a dark background

absorption line spectrum

produced by a cool gas in front of a continuous light - series of dark spectral lines among the colors of the rainbow


learned by analyzing starlight

doppler shift

allows astronomers to measure radial velocity

spectral lines

shift due to relative motion between the source and the observer

doppler effect

apparent change in wavelength of radiation caused by the relative motions of the source and observer

doppler effect

used to determine increasing distance (wavelength stretches)

doppler effect

used to determine decreasing distance (wavelength compresses)


larger doppler shifts indicate higher velocities

red shift

distance between the observer and the sources is increasing

blue shift

distance between the observer and the source is decreasing

radial velocity

learned by analyzing starlight

different types of EM radiation

require different types of telescopes

refracting telescope

uses a lens to concentrate incoming light

reflecting telescope

uses mirrors to concentrate incoming starlight

not all EM radiation

can penetrate earth's atmosphere

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