5.5.2: Electromagnetic radiation from stars Flashcards
(11 cards)
Luminosity
Total radiant power output of a star
Hertzsprung-Russell diagram
A graph of log L (luminosity in multiples of solar luminosity) on the y-axis and log T (temperature in kelvin) on the x-axis
Electron energy level
A discrete energy that an electron in an atom is allowed to possess. Energy levels in atoms are negative
Ground state
The lowest electron energy level of an atom
Emission spectrum
A set of electromagnetic frequencies produced by excited atoms and visible as bright coloured lines on a black background. Each emission is unique to an atom
Continuous spectrum
A spectrum containing all visible electromagnetic frequencies are present, for example produced by a lamp filament or other heated solid metal
Absorption spectrum
A set of electromagnetic frequencies that are missing from an otherwise continuous spectrum and shown as dark lines. The missing frequencies have been absorbed and re-emitted in all directions by atoms or molecules present in between the source and detector. The absorbed frequencies correspond to the energy levels present in the absorbing atoms or molecules
Black body
A black body absorbs all EM radiation incident on it and when in thermal equilibrium, emits a characteristic distribution of wavelengths at a given temperature
Peak wavelength of a black body
The wavelength at which the intensity is maximum for black body emission
Wien’s law
The peak wavelength is inversely proportional to the absolute temperature of a black body
λmax x T = constant
Stefan’s law
The luminosity of a star is related to its surface area, 4πr^2 and T by L = 4πr^2σT^4
