ASTR 2000 1st EditionLecture 2Light Spectra ReviewConservation of Energy Radiative Kinetic Potential How can we know about objects so far away?Studying its effect on light- Emission –matter releases energy as light- Absorption –matter takes energy from light- Transmission –matter allows light to pass through it- Reflection –matter repels light in another direction (H2O/mirrors)- Scattering –light redirected in many directions (movie screens, paper, snow)Wave Particle Duality of Light- Light can behave like a waveo Frequency, wavelength, amplitude- Light can behave like a particleo Photons –little bundles of energy*shorter the wavelength, higher the frequency*f = frequency λ = wavelength c = speed E = energy of photonLight as a Particle Energy is “proportional to” frequency - What we see as colors are different wavelengths/frequencies of lightRed~700nmYellow~550nmBlue~450nmInvisible ~outside of 350-750- Different types of light show different aspects of the UniverseRadio: longest wavelength (passes through people/buildings)Microwaves: boundary of infrared and radioInfrared: redder than red; warm objectsVisible light: what our eyes seeUltraviolet: beyond violet, produced by the hottest starsX-rays: absorbed by atoms, emitted by extreme situations/hot gas/nuclear radioactivityGamma-Rays: shortest wavelengths, intense nuclear reactions (energy not wavelength)Doppler Shif- “blue shif” –waves compressed shorter wavelength/higher frequency (moving towards you)- “red shif” –waves stretched, longer wavelength/lower frequency (moving away)Δλ = change in wavelength Δf = change in frequency v = velocity of source c = speed of waveSpectroscopy - How much light from each wavelength is emitted by an objectSpectroscope –separates out different colors/wavelengthsRefraction –depends on change of wavelength Diffraction gratings dispersion –light is bent different amounts depending on the change of wavelengthSpectrograph –main tool of astronomy Continuous Spectrum –thermal emission –opaque object with a temperatureEmission –thin hot gas –electronic transitions in atomsAbsorption –thin gas in front of a thermal source –electronic transitions + blackbody continuumElectronic transitions- Electrons occupy quantized energy levels (only certain energies are allowed)- Higher or further from the nucleus, the more energy that level has-Conservation of energy means that the change in energy has to go somewhere photons!- Emission –electron moves to a lower energy level emits photon- Absorption –photon of the right energy hits atom, electron moves up to higher energy level- The energy unit is the electron volt (eV)The -line of a series is usually brightestHydrogen –pinkHelium –peachMercury –blueSodium –yellow Barium –greenTitanium –whiteSpectra of gas clouds =chemical composition of the gasthe electrons need to be in a higher energy level - If photon energy is greater than a certain level, the electron is stripped from the atom= IONIZATION (doesn’t need to be a quantized energy anymore)Fluorescence –an atom is pumped by a high-energy photon to a higher state-electron then cascades
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