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  2. Etherington's reciprocity theorem - Wikipedia

    en.wikipedia.org/wiki/Etherington's_reciprocity...

    The Etherington's distance-duality equation has been validated from astronomical observations based on the X-ray surface brightness and the Sunyaev–Zel'dovich effect of galaxy clusters. [ 4 ] [ 5 ] The reciprocity theorem is considered to be true when photon number is conserved, gravity is described by a metric theory with photons traveling ...

  3. Distance measure - Wikipedia

    en.wikipedia.org/wiki/Distance_measure

    Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe.They are often used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the cosmic microwave background (CMB) power spectrum) to another quantity that is ...

  4. Luminosity distance - Wikipedia

    en.wikipedia.org/wiki/Luminosity_distance

    The object's actual luminosity is determined using the inverse-square law and the proportions of the object's apparent distance and luminosity distance. Another way to express the luminosity distance is through the flux-luminosity relationship, = where F is flux (W·m −2), and L is luminosity (W). From this the luminosity distance (in meters ...

  5. Cosmic distance ladder - Wikipedia

    en.wikipedia.org/wiki/Cosmic_distance_ladder

    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.

  6. Comoving and proper distances - Wikipedia

    en.wikipedia.org/wiki/Comoving_and_proper_distances

    In standard cosmology, comoving distance and proper distance (or physical distance) are two closely related distance measures used by cosmologists to define distances between objects. Comoving distance factors out the expansion of the universe , giving a distance that does not change in time except due to local factors, such as the motion of a ...

  7. Category:Physical quantities - Wikipedia

    en.wikipedia.org/wiki/Category:Physical_quantities

    This page was last edited on 24 October 2023, at 01:11 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.

  8. Astronomical unit - Wikipedia

    en.wikipedia.org/wiki/Astronomical_unit

    Distance of the outer limit of Oort cloud from the Sun (estimated, corresponds to 1.2 light-years) — Parsec: 206 265 — One parsec. The parsec is defined in terms of the astronomical unit, is used to measure distances beyond the scope of the Solar System and is about 3.26 light-years: 1 pc = 1 au/tan(1″) [6] [61] Proxima Centauri: 268 000 ...

  9. Planck units - Wikipedia

    en.wikipedia.org/wiki/Planck_units

    In any system of measurement, units for many physical quantities can be derived from base units. Table 2 offers a sample of derived Planck units, some of which are seldom used. As with the base units, their use is mostly confined to theoretical physics because most of them are too large or too small for empirical or practical use and there are ...

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