Edwin Powell Hubble (Marshfield, November 20, 1889 – San Marino, September 28, 1953) was an American astronomer.
Hubble played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects previously thought to be clouds of dust and gas, classified as “nebulae,” were actually galaxies beyond the Milky Way. He also used the strong direct evidence between the luminosity and pulsation period of a classical variable cepheid (discovered in 1908 by Henrietta Swan Leavitt) to scale galactic and extragalactic distances.
Hubble provided evidence that the recessional velocity of a galaxy increases with its distance from the Earth, a property now known as “Hubble”s law,” despite the fact that it was proposed and demonstrated observationally two years earlier by Georges Lemaître. The Hubble-Lemaître law implies that the universe is expanding. Ten years earlier, the American astronomer Vesto Slipher had evidence that the light from many of these nebulae was strongly red-shifted, indicative of high recession velocities.
Edwin Hubble”s name is easily recognized because of the Hubble Space Telescope, which was put into orbit in 1990 to study space without the distortions caused by the atmosphere.
Hubble was born in the town of Marshfield, Missouri, on November 20, 1889. He was the son of Virginia Lee Hubble (1864-1934) and John Powell Hubble, an insurance executive. In 1900, the family moved to Wheaton, Illinois. In his youth, Hubble was known more for his talents in athletics, although he got good grades in almost every subject in school except spelling. Hubble was an athlete, playing baseball, soccer, and running track at school and college. In basketball, he played various positions. In 1907, he even captained the University of Chicago basketball team and broke the Illinois state high jump record.
Hubble”s studies at the University of Chicago were concentrated in the area of law, which led him to earn a Bachelor of Science degree in 1910. As a promise to his father, he continued his studies in law, spending three years studying jurisprudence at The Queen”s College with a Rhodes Scholarship, one of the first at the university. He then studied literature and Spanish language in order to obtain a master”s degree.
In 1909, Hubble”s father moved with his family from Chicago to Shelbyville, Kentucky, later settling in the city of Louisville, also in Kentucky. His father died in 1913 while Hubble was still studying in England, and in the summer of 1913 he returned home to care for his mother, two sisters, and younger brother, along with his other brother, William. In order to accommodate William and Edwin in the same house, the family moved to another address in Louisville.
Hubble was also a dutiful son who, despite his intense interest in astronomy from childhood, agreed to his father”s request to work in the field of law, although he did manage to take some math and science courses. After his father”s death, Hubble saw no motivation to work in the field of law. So he went on to teach Spanish, physics and mathematics at New Albany High School in New Albany, Indiana, where he was also the coach of the basketball team. After a year of teaching, he entered graduate school with the help of a former University of Chicago professor to study astronomy at Yerkes Observatory, where he received his doctorate in 1917. His thesis was entitled “Photographic Investigations of Faint Nebulae”. At Yerkes, he had access to one of the most powerful telescopes of the time, which had a 61 cm reflector.
After the United States declared war on Germany in 1917, Hubble rushed to finish his thesis so that he could enlist. He then enlisted in the United States Army and was assigned to the 86th Infantry Division, where he served in the 2nd Battalion, 343 Regiment, reaching the rank of lieutenant colonel. Considered fit to serve overseas on July 9, 1918, his division never participated in combat. With the end of World War I, he spent a year at Cambridge University, where he resumed his astronomy studies.
In 1919, Hubble received an invitation to a position at the Mount Wilson Observatory of the Carnegie Institution near Pasadena, California, from George Ellery Hale, the observatory”s founder and director. Hubble remained a member of the Mount Wilson staff until his death in 1953. Shortly before his death, Hubble became the first astronomer to use the new, giant reflector on the Hale telescope at Palomar Observatory near San Diego.
Hubble also worked as a civilian for the Army, Aberdeen Proving Ground in Maryland during World War II, as head of the ballistics division of the special ballistics research laboratory. His work was facilitated by the development of several pieces of external ballistics instrumentation, the most notable development being the high-speed camera, which made it possible to study the characteristics of bombs and low-velocity projectiles in flight. The results of his studies were credited with greatly improving the design, performance, and military effectiveness of bombs and rockets. For his work there, he was awarded the Legion of Merit medal.
From the known relationship between the period and luminosity of cepheids in general, and the apparent brightness of Andromeda”s cepheids, in 1923 Hubble was able to calculate the distance between it and the Milky Way, obtaining a value of almost 1 million light-years. Even though this was an incorrect value for the distance of Andromeda, because the value is currently a little over 2 million light-years, Hubble showed that it was well beyond the limits of our galaxy, which is one hundred thousand light-years in diameter. Thus it was proven that Andromeda was an independent galaxy. The discovery went unnoticed by the press, but the following year he shared with a public health researcher a $1,000 prize given by the American Academy for the Advancement of Science. Hubble proved the existence of extragalactic nebulae consisting of independent star systems. The following year he discovered several galaxies and showed that several of them are similar to the Milky Way. The bright spot in the sky was actually a star system as large as the one in which the Sun and the Earth are situated. They were then called galaxies, by analogy with the name of our Milky Way.
After these discoveries, he began to research the structure of galaxies and classify them by shape, such as spiral or elliptical. Later, he would begin to study the distances that galaxies are from the Milky Way and their speeds in space. In 1929 he demonstrated that galaxies move apart at a great speed, and that this speed increases with distance. The relationship between speed and distance from Earth is known as Hubble”s Law, and the ratio between the two values is known as Hubble”s Constant.
This shift of galaxies would serve as the basis, in 1946, for George Gamow to establish the Big Bang theory. Analyzing the redshift in his observations, he developed the theory of the expansion of the universe and announced that the speed of one nebula relative to another is proportional to the distance between them (the so-called Hubble constant). In other words, Hubble studied the light emitted by distant galaxies, noting that the wavelength in some cases was greater than that obtained in the laboratory. This phenomenon occurs when the source and the observer move: when they move away from each other, the wavelength seen by the observer increases, and decreases when the source and observer move closer together. If a galaxy is approaching, the light shifts to the color blue, and if it is moving away, the light shifts to the color red (Doppler Effect). In each case, the relative change in wavelength is proportional to the speed with which the source is moving.
After being awarded the gold medal of the Royal Astronomical Society of London in 1940 and the United States Presidential Medal of Merit in 1946, Hubble began using the Hale telescope, completed in 1948 on Mount Palomar in Pasadena, to study faint stellar objects.
Galaxies differ greatly from each other, but the vast majority have more or less regular shapes when observed as a projection against the sky, and fall into two general classes: spirals, barred spirals, and ellipticals. Some galaxies have no definite shape, and are called irregular.
Spiral Galaxies (S): Spiral galaxies, when viewed from the front, have a clear spiral structure. Our own Galaxy is a typical spiral. They have a nucleus, a disk, a halo, and spiral arms. They are subdivided into the categories Sa, Sb, and Sc, according to how developed and coiled the spiral arms are, and how large the nucleus is compared to the disk.
Barred Spiral Galaxies (SB): About half of all discoidal galaxies have a bar-shaped structure running through the nucleus. They are called barred, and in Hubble”s classification they are identified by the initials SB. Barred galaxies are also subdivided into the SB0, SBa, SBb, and SBc categories. In barred spirals, the arms usually start from the ends of the bar. The formation phenomenon of the bar is not yet well understood, but the bar is believed to be the system”s response to some type of periodic gravitational disturbance (such as a companion galaxy), or simply the consequence of an asymmetry in the mass distribution in the galaxy disk. Some astronomers also believe that the bar is at least partly responsible for the formation of the spiral structure, as well as for other evolutionary phenomena in galaxies.
Elliptical Galaxies (E): Elliptical galaxies are spherical or ellipsoidal in shape, and have no spiral structure. They have little gas, little dust, and few young stars. They resemble the nucleus and halo of spiral galaxies. Elliptical galaxies vary greatly in size, from supergiants to dwarfs. The largest ellipticals have diameters of millions of light-years, while the smallest are only a few thousand light-years in diameter. Giant ellipticals, which have masses of up to 10 trillion solar masses, are rare, but dwarf ellipticals are the most common type of galaxy. Hubble subdivided the ellipticals into classes from E0 to E7, according to their degree of flattening. Imagine looking at a circular plate from the front, this is what an E0 galaxy looks like. Now tilt the plate so that it looks more and more elliptical and less circular, this gradual flattening represents the sequence from E0 to E7. Note that Hubble based his classification on the appearance of the galaxy, not on its true shape. For example, an E0 galaxy can either be a really spherical elliptical or a flatter elliptical seen from the front, while an E7 has to be a flatter elliptical seen from the side. But no elliptical will ever appear as flat as a spiral seen in profile.
Irregular Galaxies: Hubble classified as irregular galaxies those that were deprived of any circular or rotational symmetry, and had a chaotic or irregular structure. Many irregulars appear to be undergoing relatively intense star formation activity, their appearance being dominated by bright young stars and irregularly distributed clouds of ionized gas.
Hubble”s classification, despite all the years that have passed, continues to be used. In the 1930”s a regular at the Hubbles residence in Pasadena informed Hubble that there was movement in England, on the part of the Nobel Prize Committee, toward a possible amendment of the statutes governing the award to enable Hubble to be legally eligible for the highest honor in the natural sciences. As the 1940s approached, Hubble”s Nobel Prize situation was not resolved; by the time it was resolved that Hubble would receive the Nobel Prize, it was too late, as he had just died.
Hubble married Grace Lillian Leib (1889-1980) on February 26, 1924. Grace was the daughter of John Burke, vice president of the First National Bank and an important member of the local community. Grace studied English literature at Stanford University. Her first husband was geologist Earl Leib, who died in a tragic accident in 1921. That same year, while accompanying a friend to the Mount Wilson Observatory, she met the young astronomer Edwin Hubble, whom she married in a simple ceremony at home. The couple had no children.
Hubble had a heart attack in July 1949 while on vacation in Colorado. His wife intensified his care and changed his diet so that he could continue working. Edwin Hubble died on September 28, 1953, at the age of 63, in San Marino from a cerebral venous thrombosis. No funeral was held for him and his wife never revealed where he was buried.
Astronomers from the United States of America
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