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Hubble's law is considered the first observational basis for the expansion of the universe, and is one of the pieces of evidence most often cited in support of the Big Bang model. [8] [17] The motion of astronomical objects due solely to this expansion is known as the Hubble flow. [18]
Selected distance estimates to the Pleiades Year Distance Notes 1999 125 Hipparcos [66] 2004 134.6 ± 3.1 Hubble Fine Guidance Sensor [58] 2009 120.2 ± 1.9 Revised Hipparcos [2] 2014 136.2 ± 1.2 Very-long-baseline interferometry [62] 2016 134 ± 6 Gaia Data Release 1 [63] 2018 136.2 ± 5.0 Gaia Data Release 2 [64] 2023 135.74 ± 0.10 pc
The observational result of Hubble's law, the proportional relationship between distance and the speed with which a galaxy is moving away from us, usually referred to as redshift, is a product of the cosmic distance ladder. Edwin Hubble observed that fainter galaxies are more redshifted. Finding the value of the Hubble constant was the result ...
The distance to the open cluster Pleiades is 130 ± 10 pc (420 ± 30 ly) from us per Hipparcos parallax measurement. The centre of the Milky Way is more than 8 kiloparsecs (26,000 ly) from the Earth and the Milky Way is roughly 34 kiloparsecs (110,000 ly) across.
The Hubble volume is approximately equal to 10 31 cubic light years (or about 10 79 cubic meters). The proper radius of a Hubble sphere (known as the Hubble radius or the Hubble length ) is c / H 0 {\displaystyle c/H_{0}} , where c {\displaystyle c} is the speed of light and H 0 {\displaystyle H_{0}} is the Hubble constant .
The 2007 new Hipparcos reduction gives a statistically more accurate parallax of 8.51 ± 0.28 mas, indicating a distance of 118 ± 4 pc. [2] Analysis of Gaia parallaxes for the whole Pleiades cluster give an average distance of 136.2 ± 5.0 pc , [ 18 ] while VLBI measurements of multiple members give a distance of 136.2 ± 1.2 pc .
The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred; the Hubble law established that the further away an object is, the faster it is receding. The unexpected result was that objects in the universe are moving away from one another at an ...
This would be the "light travel distance" (see Distance measures (cosmology)) rather than the "proper distance" used in both Hubble's law and in defining the size of the observable universe. Cosmologist Ned Wright argues against using this measure. [75] The proper distance for a redshift of 8.2 would be about 9.2 Gpc, [76] or about 30 billion ...