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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.
This is the farthest distance that any photon can freely stream. Similarly, there is a "neutrino horizon" set for the farthest distance a neutrino can freely stream and a gravitational wave horizon at the farthest distance that gravitational waves can freely stream. The latter is predicted to be a direct probe of the end of cosmic inflation.
Let be a metric space with distance function .Let be a set of indices and let () be a tuple (indexed collection) of nonempty subsets (the sites) in the space .The Voronoi cell, or Voronoi region, , associated with the site is the set of all points in whose distance to is not greater than their distance to the other sites , where is any index different from .
It overtook Pioneer 11 in 1981, [13] and then Pioneer 10—becoming the probe farthest from the Sun—on February 17, 1998. [14] Voyager 2 is moving faster than all other probes launched before it; it overtook Pioneer 11 in the late 1980s and then Pioneer 10 — becoming the second-farthest spacecraft from the Sun — on July 18, 2023. [15] [16]
GN-z11 is a high-redshift galaxy found in the constellation Ursa Major.It is among the farthest known galaxies from Earth ever discovered. [5] [6] The 2015 discovery was published in a 2016 paper headed by Pascal Oesch and Gabriel Brammer (Cosmic Dawn Center).
It is described by the equation v = H 0 D, with H 0 the constant of proportionality—the Hubble constant—between the "proper distance" D to a galaxy (which can change over time, unlike the comoving distance) and its speed of separation v, i.e. the derivative of proper distance with respect to the cosmic time coordinate.
On this usage, comoving and proper distances are numerically equal at the current age of the universe, but will differ in the past and in the future; if the comoving distance to a galaxy is denoted , the proper distance () at an arbitrary time is simply given by = where () is the scale factor (e.g. Davis & Lineweaver 2004). [2]
Phobos 2: First flyby. Distance of 860 kilometres (530 mi). USSR 21 February 1989 Neptune: Voyager 2: First flyby. Distance of 40,000 kilometres (25,000 mi). USA 25 August 1989 Moon: Hiten: First lunar probe launched by a country other than the USA or USSR. Japan 18 March 1990 951 Gaspra: Galileo: First asteroid flyby. Distance of 1,600 ...