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These were the most remote objects discovered at the time. The pair of galaxies were found lensed by galaxy cluster CL1358+62 (z = 0.33). This was the first time since 1964 that something other than a quasar held the record for being the most distant object in the universe. [135] [138] [139] [136] [133] [140] PC 1247–3406: Quasar 1991 − ...
Apparent magnitude, the brightness of an object as it appears in the night sky. Absolute magnitude, which measures the luminosity of an object (or reflected light for non-luminous objects like asteroids); it is the object's apparent magnitude as seen from a specific distance, conventionally 10 parsecs (32.6 light years).
An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly 10 parsecs (32.6 light-years), without extinction (or dimming) of its light due to absorption by interstellar matter and cosmic dust. By hypothetically placing all objects at a standard ...
For objects within the Milky Way with a given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object. For objects at very great distances (far beyond the Milky Way), this relationship must be adjusted for redshifts and for non-Euclidean distance measures due to general relativity. [29] [30]
The astronomical system of units, formerly called the IAU (1976) System of Astronomical Constants, is a system of measurement developed for use in astronomy. It was adopted by the International Astronomical Union (IAU) in 1976 via Resolution No. 1, [ 1 ] and has been significantly updated in 1994 and 2009 (see Astronomical constant ).
One astronomical unit (au), the distance from the Sun to the Earth, is just under 5 × 10 −6 pc. The most distant space probe, Voyager 1, was 0.000 7897 pc from Earth as of February 2024. Voyager 1 took 46 years to cover that distance. The Oort cloud is estimated to be approximately 0.6 pc in diameter
The astronomical unit is typically used for stellar system scale distances, such as the size of a protostellar disk or the heliocentric distance of an asteroid, whereas other units are used for other distances in astronomy. The astronomical unit is too small to be convenient for interstellar distances, where the parsec and light-year are
The branch of astronomy that studies objects and phenomena outside of the Milky Way galaxy, i.e. all objects not covered by galactic astronomy. extrasolar object Any astronomical object that exists outside the Solar System. The term is generally not applied to stars or any objects larger than a star or the Solar System itself, such as galaxies.