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Welcome, my name is Phil, and in this video I explain how the Hubble constant is calculated.
The Hubble Constant, a foundational parameter in cosmological studies, denotes the rate at which the universe undergoes expansion. One method employed to determine this critical constant involves the analysis of galactic redshifts. As light emitted by distant galaxies traverses the expanding cosmos, its wavelength is stretched, leading to a shift towards longer, redder wavelengths—a phenomenon commonly referred to as redshift. This spectral alteration arises as a consequence of the universe's expansion, reminiscent of the Doppler effect observed in waves. By measuring the redshift of light emitted by galaxies, astronomers can determine the velocity at which they from Earth.
The relationship between a galaxy's redshift and its distance from Earth serves as the cornerstone of Hubble's Law. According to this fundamental law, a galaxy's recessional velocity is directly proportional to its distance from the observer. Mathematically, this relationship is expressed as v = H0 × d, where v represents the galaxy's recessional velocity, d denotes its distance, and H0 signifies the Hubble Constant. Thus, by analysing the redshifts of numerous galaxies and correlating them with their established distances, astronomers can calculate the value of the Hubble Constant.
Employing advanced methodologies, astronomers meticulously analyse the spectra of galaxies to determine their redshifts. This process entails measuring the shift of characteristic spectral lines—such as those emitted by hydrogen, towards longer wavelengths. By quantifying this redshift, astronomers can precisely determine the recessional velocity of each galaxy. When combined with accurate distance measurements—often derived from additional cosmological indicators like Type Ia supernovae or the cosmic microwave background—these redshift determinations facilitate the derivation of the Hubble Constant, thereby offering profound insights into the underlying mechanisms governing the universe's expansion.
