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[21] [22] Although not really a shortcoming, since the 1961 Hubble Atlas of Galaxies, [23] the primary criteria used to assign the morphological type (a, b, c, etc.) has been the nature of the spiral arms, rather than the bulge-to-disk flux ratio, and thus a range of flux ratios exist for each morphological type, [23] [full citation needed] [24 ...
(The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.) The Hubble distance would be the distance between the Earth and the galaxies which are currently receding from us at the speed of light, as can be seen by substituting D = cH −1 into the equation for Hubble's law, v = H 0 D.
Hubble confirmed in 1929 that the recessional velocity of a galaxy increases with its distance from Earth, a behavior that became known as Hubble's law, although it had been proposed two years earlier by Georges Lemaître. [10] The Hubble law implies that the universe is expanding. [11]
Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence , devised by Edwin Hubble and later expanded by Gérard de ...
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 ...
Hubble also demonstrated that the redshift of other galaxies is approximately proportional to their distance from Earth (Hubble's law). This raised the appearance of this galaxy being in the center of an expanding Universe, however, Hubble rejected the findings philosophically:
This method gave the distance to the Sombrero Galaxy as 29 ± 2 Mly (8,890 ± 610 kpc). [28] The second method is the surface brightness fluctuations method, which uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges appear very grainy, while more distant bulges appear smooth.
NGC 1357 has a Hubble classification of Sab, which indicates it is a spiral galaxy with no bar. It is moving away from the Milky Way at a rate of 2,018 km/s. Its size on the night sky is 3.2' x 2.4' which is proportional to its real size of the 85 000 ly.