Electromagnetic radiation from Stars Flashcards
Define luminosity.
Total radiant power output of a star, measured in W.
What is the Hertzsprung-Russell diagram?
A graph log (L/Lsolar) on the y-axis and log(T) on the x-axis. The log(T) axis runs from high values on the left to low values on the right.
Define electron energy level.
A discrete energy that an electron in an atom is allowed to possess. Energy levels in atoms are negative.
Define the ground state.
The lowest electron energy level of an atom.
Define emission spectrum.
A set of electromagnetic frequencies produced by excited atoms and visible as bright lines in spectroscopy. Each atom has a characteristic emission spectrum that represents its unique set of energy levels.
Define a continuous spectrum.
A spectrum containing all visible electromagnetic frequencies are present, for example produced by a lamp filament or other heated solid metals.
Define absorption spectrum.
A set of electromagnetic frequencies that are missing from an otherwise continuous spectrum and therefore show as dark lines on the spectrum. The missing frequencies have been absorbed and re-emitted in all direction by atoms or molecules present in between the source and detector.
Define blackbody.
A blackbody absorbs all of the EM radiation that is incident on it and when in thermal equilibrium, emits a characteristic distribution of wavelengths at a given temperature.
Define Peak wavelength.
The wavelength at which the intensity is maximum for blackbody emission.
Define Stefan’s Law.
The luminosity of a star is related to its surface area, 4πr^2, and temperature, T, by: L=4 πr2σT4, where σ= Stefan’s constant = 5.67x10-8Wm^-2k^-4.
