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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 ...
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 .
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.
Merope is too bright for Gaia to have a reliable parallax for it, but calculations of the overall distance to the Pleiades cluster using Hipparcos, Gaia, Hubble Space Telescope, and other methods repeatedly show that the Hipparcos parallaxes suffered from some kind of systemic error, and the distance to the Pleiades is most likely around 135 ...
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 ...
The Gaia Data Release 1 team were cautious about their result, and the VLBI authors assert "that the Hipparcos-measured distance to the Pleiades cluster is in error". The most recent distance estimate of the distance to the Pleiades based on the Gaia Data Release 3 is 135.74 ± 0.10 pc. [65]
H 0 is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent and which can be expressed in terms of the scale factor) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving ...
The core radius is 2.7 parsecs (8.8 light-years, a little more than the distance between the Sun and Sirius), while the half-mass radius, within which half the cluster's mass is contained, is 5.7 parsecs (19 light-years). The tidal radius of ten parsecs (33 light-years) represents the Hyades' average outer limit, beyond which a star is unlikely ...