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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 ...
Hubble radius, Hubble sphere (not to be confused with a Hubble bubble), Hubble volume, or Hubble horizon is a conceptual horizon defining the boundary between particles that are moving slower and faster than the speed of light relative to an observer at one given time. Note that this does not mean the particle is unobservable; the light from ...
Selected distance estimates to the Pleiades Year Distance Notes 1999 125 Hipparcos [67] 2004 134.6 ± 3.1 Hubble Fine Guidance Sensor [59] 2009 120.2 ± 1.9 Revised Hipparcos [2] 2014 136.2 ± 1.2 Very-long-baseline interferometry [63] 2016 134 ± 6 Gaia Data Release 1 [64] 2018 136.2 ± 5.0 Gaia Data Release 2 [65] 2023 135.74 ± 0.10 pc
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 .
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]
Distance moduli are most commonly used when expressing the distance to other galaxies in the relatively nearby universe.For example, the Large Magellanic Cloud (LMC) is at a distance modulus of 18.5, [2] the Andromeda Galaxy's distance modulus is 24.4, [3] and the galaxy NGC 4548 in the Virgo Cluster has a DM of 31.0. [4]
It differs from the “light travel distance” since the proper distance takes into account the expansion of the universe, i.e. the space expands as the light travels through it, resulting in numerical values which locate the most distant galaxies beyond the Hubble sphere and therefore with recession velocities greater than the speed of light c.
where is the curvature density and is the value of the Hubble parameter today. In the currently favoured geometric model of our Universe, the "angular diameter distance" of an object is a good approximation to the "real distance", i.e. the proper distance when the light left the object.