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The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A direct distance measurement of an astronomical object is possible only for those objects that are "close enough" (within about a thousand parsecs ) to Earth.
Instead of working with Hubble's constant, a common practice is to introduce the dimensionless Hubble constant, usually denoted by h and commonly referred to as "little h", [29] then to write Hubble's constant H 0 as h × 100 km⋅s −1 ⋅Mpc −1, all the relative uncertainty of the true value of H 0 being then relegated to h. [46]
It relates the proper distance (which can change over time, unlike the comoving distance which is constant and set to today's distance) between a pair of objects, e.g. two galaxy clusters, moving with the Hubble flow in an expanding or contracting FLRW universe at any arbitrary time to their distance at some reference time . The formula for ...
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 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 .
This video clip shows a visualization of the three-dimensional structure of the Pillars of Creation. Closer view of one pillar. Pillars of Creation is a photograph taken by the Hubble Space Telescope of elephant trunks of interstellar gas and dust in the Eagle Nebula, in the Serpens constellation, some 6,500–7,000 light-years (2,000–2,100 pc; 61–66 Em) from Earth. [1]
Hubble features a 2.4 m (7 ft 10 in) mirror, and its five main instruments observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. Hubble's orbit outside the distortion of Earth's atmosphere allows it to capture extremely high-resolution images with substantially lower background light than ground-based ...
[18] [19] The research team used Hubble's Wide Field Camera 3 to measure the distance to GN-z11 spectroscopically, measuring the redshift caused by the expansion of the universe. [20] The findings, which were announced in March 2016, revealed the galaxy to be farther away than originally thought, at the distance limit of what the Hubble ...