galactic recession

astronomy

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July 16, 2026

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Galactic recession, also known as redshift, describes the phenomenon where distant galaxies are moving away from Earth. This observation is a cornerstone of modern cosmology, suggesting that the universe is expanding.12

The concept is based on the Doppler effect, where the wavelength of light from receding objects is stretched, shifting towards the red end of the spectrum. In 1929, astronomer Edwin Hubble observed that the farther a galaxy is, the faster it recedes, a relationship known as Hubble's law. This law implies that approximately 13.8 billion years ago, all matter in the universe was concentrated in a single point, leading to the big bang. Modern estimates for the Hubble constant, which quantifies this expansion rate, place it around 67 km/sec/Mpc.1324

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cosmology
Finite or infinite?
His discovery of the systematic recession of the galaxies provided an escape, however. At first people thought that the redshift effect alone would suffice to explain why the sky is dark at night—namely, that the light from the stars in distant galaxies would be redshifted to long wavelengths beyond the…
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His discovery of the systematic recession of the galaxies provided an escape, however. At first people thought that the redshift effect alone would suffice to explain why the sky is dark at night—namely, that the light from the stars in distant galaxies would be redshifted to long wavelengths beyond the…
Read More

astronomy
Determining astronomical distances
…the speeds with which those galaxies are receding from Earth (as determined from the Doppler shift in the wavelengths of their emitted light). This correlation is expressed in the Hubble law: velocity = H × distance, in which H denotes Hubble’s constant, which must be determined from observations of the…
Read More
…the speeds with which those galaxies are receding from Earth (as determined from the Doppler shift in the wavelengths of their emitted light). This correlation is expressed in the Hubble law: velocity = H × distance, in which H denotes Hubble’s constant, which must be determined from observations of the…
Read More