15 The brightness of spectral lines depend on conditions in the spectrum’s source Law 1 A hot object or a hot, dense gas produces a continuous spectrum -- a complete rainbow of colors with without any specific spectral lines. (This is a black body spectrum.)
16 The brightness of spectral lines depend on conditions in the spectrum’s source Law 2 A hot, rarefied gas produces an emission line spectrum - a series of bright spectral lines against a dark background.
17 The brightness of spectral lines depend on conditions in the spectrum’s source Law 3 A cool gas in front of a continuous source of light produces an absorption line spectrum - a series of dark spectral lines among the colors of the rainbow.
20 But, where does light actually come from? Light comes from the movement of electrons in atoms
21 An atom consists of a small, dense nucleus surrounded by electrons
22 Atomic Vocabulary The nucleus contains protons and neutrons All atoms with the same number of protons have the same name (called an element)Atoms with varying numbers of neutrons are called isotopes.Atoms with a varying numbers of electrons are called ions.
23 Spectral lines occur when an electron jumps from one energy level to another
30 What can we learn by analyzing starlight? A star’s temperatureby peak wavelengthA star’s chemical compositionby spectral analysisA star’s radial velocityfrom Doppler shifts
31 What did you think?How hot is a “red hot” object compared to objects glowing with other colors?Of all objects that glow from heat stored or generated inside them, those that glow red are the coolest.What color is the Sun?The Sun emits all colors (wavelengths of electromagnetic radiation). The colors it emits most intensely are in the blue-green part of the spectrum.
32 Self-Check1: State the Stefan-Boltzmann law and Wien’s law and explain their meaning in the context of blackbody radiation and temperature determination.2: Describe the evidence for the particle nature of light and indicate how the energy per photon is related to the wavelength and frequency in the wave model.3: State Kirchhoff’s three laws of spectral analysis and indicate what information is derived about the nature of the light source in each case.4: Describe the Bohr model of the atom in terms of its constituents and their distribution. Explain how spectral lines can be produced by a low-density gas.5: Describe how spectroscopic analysis provides information about the chemical composition of celestial objects and indicate for which part of the object the information is valid.6: Indicate how the numbers of protons, neutrons, and electrons are used to define elements, ions, and isotopes.7: Describe the origin of line series in the hydrogen atom and explain why the Balmer lines occur at visual wavelengths but the other line series do not.8: Define excitation and ionization in the context of the Bohr model of atoms.9: Describe how the Doppler shift reveals the radial motion of the stars.