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