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Spiral galaxy UGC 12591 is classified as an S0/Sa galaxy. [1]The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. [2] [3] It is often known colloquially as the “Hubble tuning-fork” because of the shape in which it is traditionally represented.
Edwin Powell Hubble (November 20, 1889 – September 28, 1953) [1] was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology .
[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 ...
Two years later, Hubble showed that the relation between the distances and velocities was a positive correlation and had a slope of about 500 km/s/Mpc. [10] This correlation would come to be known as Hubble's law and would serve as the observational foundation for the expanding universe theories on which cosmology is still based.
Along with Philip Keenan he developed the MK system for the classification of stars through their spectra.He also developed several galaxy morphological classification systems, including the first systems to use the physical, quantifiable properties of galaxies, as opposed to simple, qualitative, eyeball estimates favoured by Edwin Hubble.
The giant elliptical galaxy ESO 325-4. An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, [1] along with spiral and lenticular galaxies.
Later in the 1920s, Edwin Hubble showed that Andromeda was far outside the Milky Way by measuring Cepheid variable stars, proving that Curtis was correct. [6] It is now known that the Milky Way is only one of as many as an estimated 200 billion (2 × 10 11) [7] to 2 trillion (2 × 10 12) or more galaxies in the observable Universe.
1923 – Edwin Hubble measures distances to a few nearby spiral nebulae (galaxies), the Andromeda Galaxy (M31), Triangulum Galaxy (M33), and NGC 6822. The distances place them far outside the Milky Way, and implies that fainter galaxies are much more distant, and the universe is composed of many thousands of galaxies.