25.1 Standard Candles
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Luminosity: Luminosity is the total power of radiation emitted by a star.
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Inverse Square Law: The inverse square law for radiant flux intensity F in terms of the luminosity L of the source is F = L /(4πd²).
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Standard Candle: An object of known luminosity is called a standard candle.
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Distance Determination: Standard candles are used to determine distances to galaxies.
25.2 Stellar Radii
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Wien’s Displacement Law: Wien’s displacement law λ max ∝ 1 / T is used to estimate the peak surface temperature of a star.
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Stefan–Boltzmann Law: The Stefan–Boltzmann law L = 4πσr²T⁴ is used to estimate the radius of a star.
25.3 Hubble’s Law and the Big Bang Theory
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Emission Spectra: The lines in the emission spectra from distant objects show an increase in wavelength from their known values.
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Redshift Formula: The redshift of electromagnetic radiation from a source moving relative to an observer is given by ∆λ / λ . ∆f/f . v / c.
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Expansion of the Universe: Redshift leads to the idea that the Universe is expanding.
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Hubble’s Law: Hubble’s law v = H0d is used to explain how the Universe is expanding and to support the Big Bang theory.