ASTR 001 Lecture Notes - Lecture 9: Inverse-Square Law, Incandescent Light Bulb, Kelvin
15 Jul 2020
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Document Summary
The motion of a light source toward or away from us changes our perception of wavelength of the waves reaching us. Light from approaching objects is blueshifted: the waves crowd together. Light from receding objects is redshifted: the waves are spaced farther apart. Temperature is a measure of internal energy and the average kinetic energy (speed) of atoms and molecules. The temperature of an object (such as a planet) is the result of an equilibrium between energy absorbed and energy emitted. Kelvin scale: water freezes at 273 k and boils at 373 k. Absolute zero is when thermal motion stops. Luminosity: amount of light leaving a source. The amount and type of light leaving a source changes as an object heats up or cools down. The hotter an object is, the more luminous it is. The hotter an object is, the bluer it is. Dense objects emit a blackbody (or planck) spectrum.
