ASTR 101 Lecture 8 Outline of Last Lecture I. Gravitational Potential EnergyII. Conservation of EnergyIII. The Force of GravityOutline of Current Lecture I. Light: The Cosmic MessengerII. Learning from Lighta. Chemical Fingerprintsb. Thermal RadiationCurrent LectureChapter 5Light: The Cosmic MessengerWavelength and Frequency- Wavelength x Frequency = speed of light = constant- l x f = c- l = wavelength, f = frequency, c = 3.00 x 108m/s = speed of light5.2 Learning from LightWhat are the three basic types of spectra?- Emission line spectrum- Continuous spectrum- Absorption line spectrum- spectra of astrophysical objects are usually combinations of these three basic typesHow does light tell us what things are made of?Chemical Fingerprints- Each type of atom has a unique set of energy levels- Each transition corresponds to a unique photon energy, frequency, and wavelength- Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths- Each type of atom has a unique spectral fingerprint- Observing the fingerprints in a spectrum tells us which kinds of atoms are presentThermal Radiation- Nearly all large or dense objects emit thermal radiation, including stars, planets, and you- An object's thermal radiation spectrum depends on only one property: its temperatureProperties of Thermal Radiation1. Hotter objects emit more light at all frequencies per unit area2. Hotter objects emit photons with a higher average energy17814524077Interpreting an actual spectrum- By carefully studying the features in a spectrum, we can learn a great deal about the object that created it.- Between blue and green on the spectrum: reflected sunlight. Continuous spectrum of visible light is like the Sun's except that some of the blue light has been absorbed - the object must look red- Thermal radiation: infrared spectrum peaks a wavelength corresponding to a temperature of 225K.- Carbon dioxide: absorption lines are the fingerprints of CO2 in the atmosphereMeasuring the Doppler Effect shif- Doppler shif tells us ONLY about the part of an object's motion toward or away from
View Full Document
Unlocking...