The main aim of cosmology is to give a unified scientific description of the whole universe. Long ago, at the origin of human civilization, the sky and the earth were considered as the only two constituents of the universe, and they were given the status of Father and Mother, respectively. With the increase in our knowledge, the sky was found to be largely populated by increasingly larger entities, consigning the earth to the position of a tiny speck in the vast universe. The earth is a part of the huge solar system, which is million times larger than the earth. The solar system itself occupies a small corner of the great system of stars known as the Milky Way. Finally, the Milky Way itself is only one among the billions of galaxies, which make up the whole universe. Modern cosmology deals with this universe. Some difficulties of cosmology arise from the fact that there is only one entity of universe at our disposal for study and further, there are limitations to complete observation of this entity itself.
Edwin Hubble Powell, born on November 20, 1889, was a distinguished American astronomer. His relevant discoveries were path-breaking contributions in the field of astronomy. He was the first person who changed our thorough view of the universe. His profound intellectual skills and ineffable abilities in science were par excellence which determined that our ‘universe is expanding’.
BIRTH AND FAMILY BACKGROUND
Edwin was born in the village of Marshfield in Missouri, USA. On the visit to their native place, enroute, he was born before his parents and grandparents. His mother, Virginia Lee James, was from Virginia City in Nevada and father, John Powell Hubble from Missouri. John was a strong Christian, who attended Drury College, Springfield. He later studied law at the Washington University and eventually became an insurance executive. John had met Virginia when he was injured in a farm accident. Being the daughter of a doctor, she cared for John during his recovery and they fell in love. They married on August 10, 1884. John and Virginia had six children : Henry, Lucy, Edwin, William, Virginia and Helen.
CHILDHOOD
He had a happy childhood, though one incident left a deep scar on his mind. Edwin and William would often become frustrated with Virginia, as she would knock down every block tower they built. As a punishment, they would step firmly on her fingers. Days later she became ill with a childhood disease and soon died. Edwin went into a deep depression, thinking her death was due to his fault. Although his understanding mother helped relieve the burden, Edwin was deeply affected by the incident.
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At a young age, Edwin had an uncanny intellect and a great liking for books, especially novels by Jules Verne and H Rider Haggard. He was especially impressed by King Solomon’s Mines. Right from childhood, Hubble had a peculiar interest in astronomy. Young Edwin corresponded with his grandfather, who once wrote to his 12-year-old grandson for questions about Mars. Edwin’s reply astonished him. His grandfather was so pleased that he had it printed in a Springfield Newspaper. This was the first glint of Hubble’s profound knowledge and interest in astronomy, which he possessed by sheer inclination. With an eye to Edwin’s personal nature, it is said, "Edwin was active and vigorous who never stepped behind, even in straits of life."
SCHOOLING
Edwin’s first big move came in 1898, when his father’s company, Old American Insurance, offered him a position in Chicago. They first moved to Evanston, but when his father obtained a pamphlet titled "Wheaton and Its Homes," their destiny was settled. This made the Hubbles move to suburban Wheaton, Illinois in 1898, where Edwin was raised. He attended high school in Chicago, Illinois, where he was promising though not an exceptional pupil. Like many youngsters, Edwin earned his first money by delivering morning papers in Wheaton. He kept abreast of academic and athletic records at school. He was probably more recognized for his athletic than academic ability. At Wheaton High School, he excelled both, as a student and as an athlete, for he actively participated in athletics and sports. At school, he had earned the reputation of a 'smart aleck' as he continually challenged and corrected his teachers. Miss Harriet Grote, his teacher appreciated his zeal for learning and adventure and had predicted that he would become one of the most brilliant man of the generation. His favorite sport at school was football. He excelled in basketball and track events in Chicago. Although he was very famous for breaking the Illinois State high jump record at High School, he earned such an excellent reputation as a boxer that a sports promoter wanted him to train for a fight with Jack Johnson, the then world heavyweight champion.
On his high school commencement day in 1906, the principal said, "Edwin Hubble, I have watched for four years and I have never seen you study even for ten minutes." It was the most embarrassing moment for Edwin, but after the brief pause he continued, "Here is a scholarship to the University of Chicago." This was his first great achievement in life. By mistake this high school scholarship was awarded to another student, thus the money had to be halved and Hubble had to fend for the rest. He paid his expenses by tutoring and carrying out summer jobs. Hubble also worked as a laboratory assistant to Robert Millikan who was well known for determining the value of the charge of an electron in his Nobel Prize winning ‘oil-drop experiment’.
UNIVERSITY OF CHICAGO
Hubble’s interest in astronomy flowered at the University of Chicago, where he was much inspired by astronomer George E Hale and probably through his contacts with the group of able teachers and research astronomers there, and at the Yerkes Observatory. At the University of Chicago, Hubble matriculated and received the degree of Bachelor of Science in 1910. A tall, elegant, dynamic and powerfully built young man, his combination of academic and athletic prowess earned him a Rhodes scholarship to Oxford in the same year when he earned his BS degree from the University of Chicago.
AT OXFORD
Hubble accepted the Rhodes Scholarship and traveled to Oxford University, England. Here, he continued his practice in athletics and sports, as he hadn’t lost his fitness or love for it. He involved himself in track events, boxing and actively participated in the baseball game, which was never played before in the British Isles. In an exhibition match of boxing against the French champion, Georges Carpentier, he performed very well. However, he planned to enter the profession of law when he was selected as Rhodes Scholar and the reason to shift his academic focus was the promise made to his dying father that he would definitely study law. He studied jurisprudence, literature, Spanish, Roman and English rather than science at Queen’s College, Oxford for two years. His time at Oxford greatly changed Hubble’s entire personality : he developed a love for tweed jackets, Dunhill pipes, sundry British pronunciations and eruptions of "bah Jove" – all of which stayed with him for the rest of his life. Hubble creditably earned his degree of Bachelor of Arts and Jurisprudence in 1912. He remained for an additional year at Oxford as a Rhodes Memorial Lecturer.
BACK TO AMERICA
On his return to the United States after completing graduation, he was admitted at the bar where he practised law half-heartedly in Louisville Kentucky. His family had already moved over there. He also took a position as a high school Spanish teacher in New Albany, Indiana. According to Hubble’s biographer Gale Christianson, though Hubble was very popular with students – especially with girls, who were evidently charmed and fascinated by his sound British diction and "Oxford mannerisms" – Hubble longed to return to science. Hubble did creditably in his job, but felt sick at heart because of his love for astronomy. His interest in astronomy however, remained with him and he had determined to chuck law for astronomy. He discontinued his practice at Kentucky bar soon after, finding himself bored with law and decided that his future lay in astronomy.
WORLD WAR I
Hubble abandoned his job and came back to the University of Chicago for post-graduate work leading to his doctoral degree in astronomy. Before he could complete the requirements for a higher degree, World War I had broken out and he joined the Officer’s Training Corps. As opportunity came his way. He completed his thesis during this period, and received the degree of Doctor of Philosophy in Astronomy in 1917.
Dr Hubble’s abilities and record as a student at Chicago and Oxford had attracted the attention of Dr Hale, the founder and director of Carnegie Institution owned Mount Wilson Observatory near Pasadena, California. Hubble’s intellect and skills as an astronomer were impressive enough to earn him a offer from the prestigious observatory. Later he became a line officer in the American Expeditionary Forces in France, and by the close of the war, had attained the rank of Major.
HUBBLE AT WILSON
After earning his Ph D degree and serving as a Major in France Ballistics, Dr Hubble returned to America and accepted the Mt Wilson appointment. The completion of the 100-inch telescope necessitated fresh operating force. Hale offered Hubble a position on the research staff in 1919 and thereby Hubble started his long, fruitful and future oriented career at Mt Wilson studying faint, hazy blobs of light called nebulae that would one day make him famous.
Hubble made his debut on the mountain above Pasadena just three weeks after the unveiling of 100-inch Hooker telescope, the biggest on the planet, which had taken more than a decade to build and install. He invariably introduced himself – arrived at observatory headquarters, still in uniform but ready to start observing with the just completed Hooker Telescope, the most powerful telescope on earth. This telescope employed the most advanced technologies of that time.
Hubble had to share the Hooker telescope with other staff members, but whenever his turn came around, he spent frigid nights below the open observatory dome photographing nebulae. Perched in a small viewing platform high above the concrete floor, the "assistant astronomer" tipped his chair precariously forward as he looked into the eyepiece, little puffs of smoke rising from his pipe towards the heavens.
Hubble encountered his greatest scientific rival, Shapely for the first time at observatory, where the sprawling sky was not obscured by radiant ground light and automobile smog. Hubble was new on the staff, a 29-year-old Major back from World War I, while Shapely was an old hand who at 33 was already ranked as one of the country’s leading explorers of the Milky Way.
HUBBLE AND SHAPLEY
It is said that, Hubble had built his reputation on the ruins of one of Shapley’s most famous theories. Hubble was a native Missourian like Shapely. Like him, he was highly ambitious, but otherwise he was his opposite. He was the son of an insurance executive while Shapely was the son of a hardscrabble farmer. Hubble was a square-jawed, aristocratic snob, tall and reserved while Shapely was a salt-of-the earth type, round faced and smiley. Being a Rhodes Scholar at Oxford, Hubble was addicted to the high life. But schooling at Princeton had not erased Shapely’s countrified accent nor his disdain for high-hats. The rivalry between the two was always on its personal edge.
Harlow Shapely already made his reputation by measuring the size of the Milky Way. Using the bright stars called Cephied variables as standardized light sources, he gauged the galaxy as being an astounding 300,000 light years across, 10 times as big as anyone had thought. Yet, Shapely claimed that the Milky Way was the whole cosmic ball of wax. The luminous nebulae were, he insisted, just what they look like : clouds of glowing gas that were relatively nearby. He disputed suggestions dating from William Herschel in the 18th century that nebulae, the faint, gassy-looking blobs in the sky, might be other galaxies. Shapely argued that the Milky Way was the universe entire. Among those who were unconvinced was Hubble, who studied nebulae at the University of Chicago and proclaimed in his doctoral dissertation that discovery of their nature awaited more powerful telescopes.
In 1921, Shapely departed from Hubble to take over the Harvard Observatory as he made a calamitous career move. He left the Mount Wilson Observatory for the Harvard faculty and directorship of Harvard College Observatory. The job was plum, but its cost was relocating 3,000 miles away from Mount Wilson’s new telescope, the biggest on the planet.
REDEFINING UNIVERSE
In October 1923, Hubble spotted what he thought were several novae (stars flaring up dramatically) in the Andromeda Nebula. Upon examining photo plates of the same region made years earlier by other astronomers, including Shapely, he found that one "nova" was actually a Cepheid. As such, its distance from earth could be calculated by the same method Shapely had used to gauge the size of the Milky Way. Spotting a Cepheid variable star in the Andromeda Nebula, Hubble used Shapley’s technique to show that the nebula was nearly a million light years away, far beyond the bounds of the Milky Way. It’s now known to be the full-fledged galaxy closest to our own in a universe that contains tens of billions of galaxies. Now, Hubble knew that if the Andromeda Nebula was a galaxy, countless other nebulae were likely galaxies as well. He continued to observe the Cepheid to make sure he had made no error.
And in 1924, three years after Shapely took over the Harvard Observatory, Hubble found proof to the contrary. Hubble measured the distance to the Andromeda Nebula, a faint patch of light with about the same apparent diameter as the moon and showed it was about a hundred thousand times as far away as the nearest stars. It had to be a separate galaxy, comparable in size to our own Milky Way but much further away. Consequently, Hubble was now confident enough to write to Shapely, taunting him with the evidence contradicting his theories : "You will be interested to hear that I have found a Cepheid variable in Andromeda Nebula. I have a feeling that more variables will be found by careful examination of long exposures. Altogether, next season should be a merry one." After Shapely read Hubble’s letter, he handed it to a colleague, conceding : "Here is a letter that has destroyed my universe." In reply to Hubble, Shapely wrote in a letter : "I do not know, whether I am sorry or glad to see this break in the nebular problem. Perhaps both." Biographer Christianson quoted this from Shapley’s letter to Hubble. However, Shapely called Hubble’s letter, "the most interesting piece of literature I have seen for some time."
He went on to raise critical questions about the sightings. Months later, Hubble wrote to Shapely again to report more Cepheids in Andromeda and in other nebulae : "The straws are all pointing in one direction." The New York Times carried the word to the masses in a 30-lined story headlined : "Finds Spiral Nebula Are Stellar Systems. Doctor Hubble confirms view that they are ‘island universes’ similar to our own."
Whether or not the light pinpoints on Hubble’s photographic plate were really stars, Shapely and other members of the island universe hypothesis dismissed them as curds in a Laplacian nebulae. Henrietta’s Cepheid variable stars provided the needed mileposts. Henrietta also knew very little that the mileposts were already there. Cepheids are bright enough to be seen across intergalactic distances. Using the new 100-inch telescope at Mount Wilson, Hubble photographed the spirals again and again comparing the plates to find stars that had been varied in brightness. Hubble deduced that Andromeda lies about one million light years away, but it was really about million and one light years away. He estimated half the distance of later ones but clearly sufficient to establish that the spiral was well beyond even Shapley’s "big galaxy".
MARRIAGE
On February 26, 1924, Hubble was married to beautiful Grace Burke whom he met on Mount Wilson Observatory, Pasadena, California, for the first time. Mrs Hubble said that the first description of her future husband was given to her by W H Wright, at that time an astronomer in the Lick Observatory. Grace was the widow of Warren Russel Leib, a businessman killed in a mining accident. Edwin wanted to take up law again so that Grace could continue her high standard of living. But she disliked the idea as it meant that Edwin had to forsake his love for stars. Later they had a three-month long honeymoon in Europe. They built a house at Pasadena and enjoyed their life among the Hollywood stars.
HUBBLE AND CEPHEID VARIABLES
The same year Hubble announced the discovery of the presence of Cepheid variables in extra-galactic nebulae. Hubble’s scientific reputation was made almost overnight by his discovery that the universe is vast and the Milky Way insignificant. The discovery of extra-galactic nebulae required the full light-gathering power and resolution of the 100-inch telescope, and Dr Hubble at once recognized its vital importance.
Before 1924, Hubble’s earlier investigations were made chiefly with the 60-inch telescope and consisted of studies on monetary nebulae, nebulous stars, novae, and stars variable in light. All these objects are within our own galaxy, and it is interesting to trace the development of Hubble’s methods and conceptions as he went further and further outward, and finally arrived at the extra-galactic nebulae, the study of which formed the major portion to his life’s work. Through his photometric and spectroscopic observations, Hubble was able to draw important conclusions regarding the source of luminosity in diffused nebulae in addition to the discovery of many new planetary nebulae and various stars. In a series of publications between 1924 and 1930, Hubble applied the Cepheid criterion to several of the well-observable nebulae, obtained over relatively accurate distances, and settled once and for all, the vexed question whether these objects are independent galaxies in space or not.
Soon after discovering the existence of these external galaxies, Hubble creditably undertook the task to classify them. With the help of his sufficiently accumulated observational material, Hubble was able to establish a classification of nebulae, including both galactic and extra-galactic objects, into groups according to luminosity, degree of concentration of diffuseness, brightness, and form, whether elliptical, spiral or irregular.
DOPPLER EFFECT
Hubble began to measure the distance from earth to the galaxies that he classified. He used information provided by Cepheid stars with their respective galaxies to measure their distance from earth. He compared these distance measurements to measurements of the galaxy's movement with respect to earth. The great progress in the determination of the distances of the brighter extra-galactic nebulae through the use of the Cepheid variables discovered in them, and certain features such as size, luminosity, and physical nature, which were found to provide approximate distances for the fainter nebulae, lent exceptional interest to the study of their motions. Because of the enormous distances of even the nearest of these objects, no certain cross-motion can be measured, but the spectrograph can of course give the motion in the line of sight or radial velocity. Several astronomers, in particular, American astronomer Vesto Slipher, studied the speed of the galaxies in the 1910s and 1920s, before Hubble classified them as galaxies. The astronomers measured the galaxy’s speed by measuring the red shift of the galaxy. Red shifts result from radiation that an object emits. The radiation will appear to shift in wavelength if the object is moving with respect to the observer. If the object is moving away from the observer, each wave will leave slightly further away from the wave than it did before, increasing the distance between the waves. The wavelength of an object’s radiation will seem shorter if the object is moving towards the observer. This is called the Doppler Effect.
Dr Slipher, an astronomer at the Lowell Observatory, some years ago succeeded in measuring the radial velocities of a moderate number of the brighter extra-galactic nebulae he had observed that were receding from the earth with high average velocities. This was the earliest evidence for the theory of the ‘expanding’ universe.
In 1927, Belgian scientist George Lemaitre had developed a model of the universe that incorporated the general theory of relativity of German American physicist Albert Einstein. Lemaitre’s model showed an expanding universe, but Hubble’s measurements were the first real evidence of this expansion. Hubble was able to measure the distances to only a handful of other galaxies, but he realized that as a rough guide he could take their apparent brightness as an indication of their distance.
The speed with which a galaxy was moving toward or away from us was relatively easy to measure due to the Doppler Shift of their light. Just as a sound of a racing car becomes lower as it speeds away from us, so the light from a galaxy becomes redder. Though our ears can hear the change of pitch of the racing car engine, our eyes can’t detect the tiny red shift of the light, but with a sensitive spectrograph, Hubble could determine the red shift of light from distant galaxies.
Hubble realized the importance of this investigation to our views of the nature of the universe and theories of cosmogony. Dr Hubble and his assistant Milton Humason began measuring the radial velocities of extra-galactic nebulae down to as faint a limit as possible. Dr Mayall of the Lick Observatory also joined in the plan. Conditions seemed almost to be favorable. Much more accurate distances of these nebulae were now known. The observational data available to Hubble by 1929 was sketchy, but whether guided by inspired instinct or outrageously good fortune, he correctly defined a straight line fit between the data points showing the red shift was proportional to the distance. Hubble discovered the most interesting result that out of the limits of the observations, the radial velocity was related directly to the distance of the nebula observed, and that this relationship was a linear one. The more distant the nebulae, the faster it was moving.
HALE TELESCOPE
The 100-inch telescope was available, especially for the fainter objects, and the construction of the 200-inch Hale Telescope was in progress. The early investigation of Slipher attained a limit of somewhat less than 2,000 km/s in the radial velocities of the nebulae observed. Humason reached 45,000 with the 100-inch telescope, and so far somewhat more than 60,000 with the 200-inch Hale Telescope. Whether the linear relationship of velocity and distance will persist out to the observable limit of this telescope is still uncertain, but the evidence for its reality seems to be conclusive up to a distance of half-a-billion light years. Hubble’s greatest discovery came in 1929, when he determined that further a galaxy is from the earth, the faster it appears to move away. This notion of an ‘expanding’ universe formed the basis of the Big Bang theory, which states that the universe began with an intense burst of energy at a single moment in time – and has been expanding ever since. The same year he wrote a paper, A Reflection on the Distance and Radial Velocity among Extra-galactic Nebulae.
HUBBLE AND EINSTEIN
The conclusion of Hubble’s discovery that the universe is expanding was almost extraordinary, mind-blowing, and yet seemed inescapable. When Einstein heard of Hubble’s discovery, he was elated. More than a decade earlier his general theory of relativity told him that the universe must either be expanding or contracting, yet some astronomers had told him it was doing neither. Against his better judgment, Einstein had argued his elegant equations with an extra-factor he called the cosmological constant – a sort of antigravity force that kept the universe from collapsing in on it. But suddenly, the cosmological constant was unnecessary. Einstein’s instincts had been right, after all. Einstein’s great blunder had been to doubt himself but Hubble’s discovery had repaired what Einstein referred to as "the greatest blunder of my life." During a visit to Caltech, the great and grateful physicist traveled to the top of Mount Wilson to see the telescope and thank Hubble personally for delivering him from his folly.
It is perhaps not altogether certain that, whether Dr Hubble reserved judgment on the question whether the huge displacements observed in the lines of the extra-galactic nebulae are due to actual motion, or whether to some hypothetical cause such as a possible fatigue of light in its passage through space : is perhaps not altogether certain. Hubble was mostly impressed by two considerations. First, that motion producing the Doppler Effect is the only known cause of any considerable bodily displacements of spectral lines; secondly that the systematic displacements of all lines is the spectra of stars in our galaxy, which are universally ascribed to motion, indicate a range in radial velocity of some 700 km/s, a considerably larger value than that of numerous extra-galactic nebulae. Therefore, there was no particular necessity for introducing a different cause for the displacements observed in these distant nebulae from that operating among the stars of our own galaxy. This view was adopted and mentioned by Hubble in several publications relating to the expanding universe.
THE REALM OF THE NEBULAE
In 1936, Hubble wrote the book on his discoveries, The Realm of the Nebulae which cemented his public reputation. During the period preceding the World War II, problems relating the physical nature and the distribution of nebulae, the direction of rotation of spirals, the motion of our galactic system among the nebulae, and several other allied investigations indicate the extent of Hubble’s activities and efforts. At this time, he reached a very important conclusion that on a large scale the extra-galactic nebulae are distributed fairly uniformly throughout space, a valuable contribution to theories of cosmogony. In his book many of the results of his investigations were summarized in detail. Tourists and Hollywood luminaries alike would drive up the mountain to marvel at the observatory where Hubble had discovered the universe, and he and his wife Grace were embraced by the elite of California society. Hubble was not universally admired among his peers as some considered him arrogant. But Hubble’s findings made him an overnight scientific authority and a celebrity. Hubble was a close confidant of Aldous Huxley, a friend to Charlie Chaplin, Helen Hayes and William Randolph Hearst. Hubble and his wife were also friends with Anita Loos, author of Gentlemen Prefer Blondes.
MEDAL OF MERIT
Hubble worked at the Mount Wilson observatory until the summer of 1942, when he left to do war work at the Aberdeen Proving Ground. His scientific career was punctuated by service in both the World Wars. Hubble’s last contribution to astronomy was a key role in the construction of the Hale telescope. Four times as powerful as the Hooker, the Hale would be the largest telescope on Earth for over 40 decades. It would have been even longer but its completion was interrupted by World War II, as the ex-major was signed on as head of ballistics at Aberdeen Proving Ground, in Maryland. For his valuable service during the war, his country awarded him the Medal of Merit, in 1946.
BACK TO WILSON
Hubble returned from the Ballistics Research Laboratory at Aberdeen after World War II. He returned to his position at the Wilson Observatory. He devoted much time on plans relating to the 200-inch telescope and its program of research. The construction of this instrument was very well advanced, and Hubble was placed upon the committee, as the project incharge. He also took very deep interest in the 48-inch Schmidt Telescope, which was planned as an adjunct to the large reflector : his wide experience having shown the value of a powerful instrument of large angular field and great light-efficiency for studies of the fainter nebulae. Hubble was wholly responsible for conceiving and working out the details of the major project of a survey with this telescope. This survey covers the whole area of sky observable from the latitude of Palomar mountain. This survey was financed by the National Geographic Society and known as the National Geographic Society – Palomar Observatory Sky Survey. These observations required the photography on pairs of glass plates, suitably curved, and with emulsions sensitive to blue light and red light, respectively of adjoining areas of sky. This investigation made considerable progress, and required few years for completion.
Hubble had looked far into space as the Hooker telescope could. Further exploration had to await the 200-inch Hale telescope at Mount Palomar, which was not completed until 1948, near the end of his life. Hubble needed to be one-up on everyone else, so he hungered for more knowledge. He once chafed when an old adversary, Adriaan Van Maneen, was slated to sit at the head of the dining table on Mount Wilson. It was his due as the astronomer using the Hooker telescope that night Hubble strode into the hall early and swapped napkin rings, leaving his own in the prime spot. Van Maneen, visibly perplexed, took the lesser seat without any protest. Hubble’s another trick was to memorize obscure facts from the Encyclopaedia Britannica and then deftly steer the conversation to that very topic. After his companions showed their ignorance, he would impress them with his expertise and casually reach for the Britannica for verification. In 1951, even Pope Pius XII mentioned Hubble’s work favorably. The Vatican, which had long since made peace with astronomy, viewed the expanding universe as compatible with religious creation scenarios.
HALE TELESCOPE
The 100-inch telescope was available, especially for the fainter objects, and the construction of the 200-inch Hale Telescope was in progress. The early investigation of Slipher attained a limit of somewhat less than 2,000 km/s in the radial velocities of the nebulae observed. Humason reached 45,000 with the 100-inch telescope, and so far somewhat more than 60,000 with the 200-inch Hale Telescope. Whether the linear relationship of velocity and distance will persist out to the observable limit of this telescope is still uncertain, but the evidence for its reality seems to be conclusive up to a distance of half-a-billion light years. Hubble’s greatest discovery came in 1929, when he determined that further a galaxy is from the earth, the faster it appears to move away. This notion of an ‘expanding’ universe formed the basis of the Big Bang theory, which states that the universe began with an intense burst of energy at a single moment in time – and has been expanding ever since. The same year he wrote a paper, A Reflection on the Distance and Radial Velocity among Extra-galactic Nebulae.
HUBBLE AND EINSTEIN
The conclusion of Hubble’s discovery that the universe is expanding was almost extraordinary, mind-blowing, and yet seemed inescapable. When Einstein heard of Hubble’s discovery, he was elated. More than a decade earlier his general theory of relativity told him that the universe must either be expanding or contracting, yet some astronomers had told him it was doing neither. Against his better judgment, Einstein had argued his elegant equations with an extra-factor he called the cosmological constant – a sort of antigravity force that kept the universe from collapsing in on it. But suddenly, the cosmological constant was unnecessary. Einstein’s instincts had been right, after all. Einstein’s great blunder had been to doubt himself but Hubble’s discovery had repaired what Einstein referred to as "the greatest blunder of my life." During a visit to Caltech, the great and grateful physicist traveled to the top of Mount Wilson to see the telescope and thank Hubble personally for delivering him from his folly.
It is perhaps not altogether certain that, whether Dr Hubble reserved judgment on the question whether the huge displacements observed in the lines of the extra-galactic nebulae are due to actual motion, or whether to some hypothetical cause such as a possible fatigue of light in its passage through space : is perhaps not altogether certain. Hubble was mostly impressed by two considerations. First, that motion producing the Doppler Effect is the only known cause of any considerable bodily displacements of spectral lines; secondly that the systematic displacements of all lines is the spectra of stars in our galaxy, which are universally ascribed to motion, indicate a range in radial velocity of some 700 km/s, a considerably larger value than that of numerous extra-galactic nebulae. Therefore, there was no particular necessity for introducing a different cause for the displacements observed in these distant nebulae from that operating among the stars of our own galaxy. This view was adopted and mentioned by Hubble in several publications relating to the expanding universe.
THE REALM OF THE NEBULAE
In 1936, Hubble wrote the book on his discoveries, The Realm of the Nebulae which cemented his public reputation. During the period preceding the World War II, problems relating the physical nature and the distribution of nebulae, the direction of rotation of spirals, the motion of our galactic system among the nebulae, and several other allied investigations indicate the extent of Hubble’s activities and efforts. At this time, he reached a very important conclusion that on a large scale the extra-galactic nebulae are distributed fairly uniformly throughout space, a valuable contribution to theories of cosmogony. In his book many of the results of his investigations were summarized in detail. Tourists and Hollywood luminaries alike would drive up the mountain to marvel at the observatory where Hubble had discovered the universe, and he and his wife Grace were embraced by the elite of California society. Hubble was not universally admired among his peers as some considered him arrogant. But Hubble’s findings made him an overnight scientific authority and a celebrity. Hubble was a close confidant of Aldous Huxley, a friend to Charlie Chaplin, Helen Hayes and William Randolph Hearst. Hubble and his wife were also friends with Anita Loos, author of Gentlemen Prefer Blondes.
MEDAL OF MERIT
Hubble worked at the Mount Wilson observatory until the summer of 1942, when he left to do war work at the Aberdeen Proving Ground. His scientific career was punctuated by service in both the World Wars. Hubble’s last contribution to astronomy was a key role in the construction of the Hale telescope. Four times as powerful as the Hooker, the Hale would be the largest telescope on Earth for over 40 decades. It would have been even longer but its completion was interrupted by World War II, as the ex-major was signed on as head of ballistics at Aberdeen Proving Ground, in Maryland. For his valuable service during the war, his country awarded him the Medal of Merit, in 1946.
BACK TO WILSON
Hubble returned from the Ballistics Research Laboratory at Aberdeen after World War II. He returned to his position at the Wilson Observatory. He devoted much time on plans relating to the 200-inch telescope and its program of research. The construction of this instrument was very well advanced, and Hubble was placed upon the committee, as the project incharge. He also took very deep interest in the 48-inch Schmidt Telescope, which was planned as an adjunct to the large reflector : his wide experience having shown the value of a powerful instrument of large angular field and great light-efficiency for studies of the fainter nebulae.
Hubble was wholly responsible for conceiving and working out the details of the major project of a survey with this telescope. This survey covers the whole area of sky observable from the latitude of Palomar mountain. This survey was financed by the National Geographic Society and known as the National Geographic Society – Palomar Observatory Sky Survey. These observations required the photography on pairs of glass plates, suitably curved, and with emulsions sensitive to blue light and red light, respectively of adjoining areas of sky. This investigation made considerable progress, and required few years for completion.
Hubble had looked far into space as the Hooker telescope could. Further exploration had to await the 200-inch Hale telescope at Mount Palomar, which was not completed until 1948, near the end of his life. Hubble needed to be one-up on everyone else, so he hungered for more knowledge. He once chafed when an old adversary, Adriaan Van Maneen, was slated to sit at the head of the dining table on Mount Wilson. It was his due as the astronomer using the Hooker telescope that night Hubble strode into the hall early and swapped napkin rings, leaving his own in the prime spot. Van Maneen, visibly perplexed, took the lesser seat without any protest. Hubble’s another trick was to memorize obscure facts from the Encyclopaedia Britannica and then deftly steer the conversation to that very topic. After his companions showed their ignorance, he would impress them with his expertise and casually reach for the Britannica for verification. In 1951, even Pope Pius XII mentioned Hubble’s work favorably. The Vatican, which had long since made peace with astronomy, viewed the expanding universe as compatible with religious creation scenarios.
EDWIN HUBBLE
In Britain, Punch versified,
" When life is full of trouble,
And mostly froth and bubble,
I turn to Dr Hubble,
He is the man for me."
Dr Edwin Powell Hubble, an aesthetic American astronomer is universally acknowledged as having been one of the foremost astronomers of the modern era.
Astronomers have discovered pulsars, quasars, black holes and planets that orbit the distant suns. But all these prove to be a shade paler in comparison to the discoveries that Edwin Hubble made in the few remarkable years during the 1920s. Most of his colleagues believed that the Milky Way is a swirling collection of stars, a few hundred thousand light years away, that made up the entire cosmos. But his deep search into space from the chilly summit of Mount Wilson, in southern California, helped him determine that the Milky Way is just one of millions of galaxies that dot an incomparably larger setting.
From his central role, in the so grand a problem, Hubble has become a legend. He possessed the most remarkable ability to cut the core of unsolved problems concerning the field of astronomy. From 1824 to 1936, he had set down the significant foundations upon which observational cosmology rests today. He is best remembered as the founder of observational cosmology and explorer of the distant cosmos.
November 20, 1889
Edwin Hubble was born in the village of Marshfield, Missouri, USA.
1898
Hubble’s family moved to Chicago.
1910
Hubble earned an undergraduate degree in mathematics and astronomy and a reputation as a fine boxer.
1912
Hubble turned away from both, athletics and astronomy, preferring to study law as a Rhodes Scholar at the Oxford University.
1913
Hubble returned to the United States and was admitted to the bar where he practiced law briefly in Louisville, Kentucky.
1914
Hubble began studies for an astronomical career at the Yerkes Observatory.
1917
Received the degree of Ph D in Astronomy.
1919
Hubble began to work at Mount Wilson Observatory in California, making discoveries concerning extra-galactic phenomena.
February 26, 1924
Hubble married Grace Burke whom he met on Mount Wilson, California.
1931
Einstein thanked Hubble for making his discovery of expanding universe leading to the abandonment of the Universal Constant, and visited him at Mount Wilson.
1935
Hubble teamed with R C Tolman in Astronomical Research.
Two methods of investigating the nature of the Nebular Red Shifts written by Edwin Hubble and Richard Tolman was published.
1936
Hubble wrote the book The Realm of Nebulae.
1937
The Observational Approach to Cosmology was published.
1942
The Problem of Expanding Universe was published.
1942
Hubble left Mount Wilson.
1943
Hubble becomes temporary head of Army Ballistics.
1946
Hubble was awarded the Medal of Merit for his valuable service to his country.
1948
Hubble was elected Honorary Fellow of Queen’s College, Oxford, for his notable contributions to Astronomy.
September 28, 1953
Hubble died of cerebral thrombosis.
HUBBLE’S APPROACH TO SOLUTIONS
The most interesting personal aspects of the life of the world’s greatest scientists are in understanding how they approach at solutions. The solutions themselves must be independent of the personality, otherwise, the results have no objective reality. Yet, the internal excitement in arriving at solutions is never this cold within the personality itself. It is said that, "Every scientist lives in a world of imagination." The grander the problem, the more wonderful must be the imagination. And Hubble lived with an ineffable problem – the discovery of the structure of the world on the largest scale. It is widely believed that, the work by him and by others of his generation, some faint transient appearance of a "creation event of the universe," became available to science by an objective method, not as in other times, by metaphysics or speculation. Hubble must have understood more clearly than anyone else, what he was dealing with and what he had accomplished. The realization that an understanding had finally been reached on the way the universe is organized, and above all, the discovery of its expansion, must have borne influence in some way as to how Hubble lived with everyday events.
FOUR CENTRAL ACCOMPLISHMENTS
From 1922 to 1936, Hubble put forth the solution of four central and overwhelming problems, any one of which would have guaranteed him a position of the first rank in history.
(a) From 1922 to 1926 Hubble proposed a classification system for nebulae, both galactic and extra-galactic. The galaxy classification system has become the Hubble morphological sequence of galaxy types.
(b) In 1924, with the discovery of Cepheids in NGC 6822, with parallel work in M33 and M31, Hubble settled decisively the question of the nature of the galaxies, whose correct solution, to be sure, had previously been given using what many believed to be inconclusive arguments, by Curtis, Lundmark and Opik.
(c) From 1926 to 1936, the distribution of galaxies that averaged over many solid angles, was determined to be homogeneous in distance. The test was made by showing that the coefficient of the log N(m) count distribution with magnitude has a value of about 0.6 at bright magnitudes. Thus, it is proved that galaxies truly mark a space which is significant to the universe itself. Mount Wilson 100-inch telescope were then used to attempt a measurement of the radius of curvature of space by finding deviations of the coefficient from the Euclidean value of faint magnitudes.
(d) In 1929, the linear velocity–distance relation was set out in a discovery paper. This was followed by a series of papers with Humason between 1931 and 1936 that verified and extended the relation of large Red shifts. This discovery lead to the notion of the expanding universe, which is the center-piece for the cosmological models of the present day.
THE PUBLISHED PAPERS
(a) THE HUBBLE CLASSIFICATION SEQUENCE
Before 1926, no satisfactory classification system for galaxies existed. At that time, two similar systems appeared in the literature, following discussions at the 1925 meeting of the International Astronomical Union in Cambridge, England. Before 1925, a purely descriptive system set up by Wolf in 1908 had been used. This system was generally considered to be in need of revision as the classification showed no continuity between the Wolf types. In his Ph D thesis, Hubble had remarked that the Wolf classification “while admittedly formal, offers an excellent scheme for temporary filing until a significant system shall be constructed”, and later in the same publication “the Wolf system is wholly empirical and probably without physical significance, yet offers the best available system of filing away data and will later be on great service when a significant order is established”.
One can note that, the construction of these two quotations shows, that Hubble already possessed the confidence to accomplish what lay ahead when he entered the field. The surety of language characterized many of his later writings – a surety that was intended to conquer the field by prose as well as by the technical results. Hubble’s mastery of the language was so excellent, that gave some of his papers much dominance over prior work by others. Often, Hubble solved the problem, without the same elegance of style, power of presentation, and excellence of summary possessed by him when he was at his best.
Hubble gave the barest outline of a new classification scheme in his fundamental paper on the nature of diffuse galactic nebulae. Four years later, the scheme was expanded and illustrated by photographic panels. Clarifying comments by Hubble in 1927 that answered criticisms by Reynolds, and a slightly expanded explanation set out in Chapter V of The Realm of Nebulae, was the intent to which Hubble amplified his 1926 discussion of the galaxy classification system. But the Hubble classification sequence has become so widely used that it is a curiosity to note that Hubble, in his reply to the comments by Reynolds, describes his principal announcement of the 1926 system merely as “a preface to some general statistical investigations”.
Yet, Hubble never took his ‘preface’ seriously. He gave it priority in a revealing footnote in part I of his 1926 paper. There, he comments on a classification system proposed at about the same time by his contemporary, Lundmark. Some of Hubble’s complaints were unfounded, which he rarely made public, showing a sensitivity he generally kept hidden. Some of Hubble’s accusations are addressed in a partially justifiably acerbic reply by Lundmark. These accusations are addressed also in a footnote, in Lundmark’s near great but largely neglected paper.
CLASSIFICATION OF GALAXY
From 1925, Hubble studied the structure of these external galaxies and classified them according to their shape and composition into regular and irregular forms. The regular galaxies, 97 per cent of the total, had elliptical or spiral shapes. Hubble further divided the spiral galaxies into normal spiral galaxies and barred spiral galaxies.
Hubble’s work classifying galaxies is hardly unimportant, yet it pales in comparison with his far-reaching discoveries. Hubble grouped galaxies into three main categories :
SPIRALS – with arms winding around a central nucleus; our Milky Way for instance, is a spiral.
ELLIPTICALS – found in a variety of rounded shapes.
IRREGULARS– come in plenty of peculiar forms.
There are no distinct boundaries between the types of galaxies – some galaxies have the characteristics of both spiral and elliptical galaxies, and some spiral galaxies could be classified as either normal or barred.
Irregular Galaxies – galaxies that seem to have no regular shape or internal structure – made up only three per cent of the galaxies that Hubble found.
(b) CONFIRMATION ON EXPANDING GALAXIES
In the early 20th century, before Hubble began his extensive work, there was an intense debate raging in the field of astronomy over great clusters of stars, called ‘nebulae’. At the time, there were galaxies in the universe that lay beyond the Milky Way. The issue then was, whether these ‘nebulae’ were a part of the Milky Way or some other star formations beyond our galaxy. In some ways, it is more difficult to comprehend that the existence of other galaxies was uncertain in such recent years than to believe that Copernicus was doubted in the 16th century for proposing the idea of a solar system.
Hubble discovered many other nebulae that contained stars and were located outside of the Milky Way. He found that they contained objects similar to those within the Milky Way. These objects included round, compact groups of stars called globular clusters and stars called novas that flare suddenly in brightness.
In 1924, Hubble finally determined that these ‘nebulae’ are indeed other galaxies because they are moving away from the earth. In fact, he concluded that these star systems are each ‘island universe’, not part of our own galaxy. This was an enormously important discovery, for it opened up a great new realm of research and provided an important base for the theory of the expanding universe.
(C) DISTRIBUTION OF GALAXIES IN SPACE
From the very beginning of his fruitful career, Hubble was intrigued with the distribution of nebulae. His work on the problem began with his Ph D research, elementary as this now appears. With the final proof that galaxies are beyond the Milky Way, the major problem then became whether they are fair makers of the universe, or if they are merely part of a hierarchical structure in a next rung, up in the organization of matter. The solution rested on the way galaxies are distributed in distance. If they increase in numbers in proportion to the surveyed volume, they would then clearly be the basic unit of the distribution.
The obvious test could be made using galaxy counts to various magnitude limits. From his work on the galaxy luminosity function, Hubble knew that galaxies have spread in absolute magnitude. Nevertheless, as long as the luminosity function does not diverge at the faint end, the counts to different limits of magnitude will exhibit a distribution that varies regardless of the form of the luminosity function, provided that the objects are distributed homogeneously in distance.
With the help of this knowledge, the early aim of Hubble’s work on counts was to determine the numerical value of the coefficient of the magnitude term. In the first discussion in his remarkable 1926 paper, Hubble shows that the data were consistent indicating homogeneity. But it was very clear that the data could be fundamentally improved and carried to fainter magnitudes by using the enormous power of the 100-inch reflector. Hubble began a massive observation program and the results began to appear in a series of papers that was to culminate in the attempt to measure the curvature of space.
After some years, the detailed paper on the distribution appeared. As in the Cepheid work few years earlier, this paper was so thoroughly convincing that it brought the problem of the mean galaxy distribution. The paper has become a classic. Its power lies in the large amount of new data presented and in Hubble’s straightforward, seemingly simple analysis of them – a characteristic of much of Hubble’s work.
(d) THE RED SHIFT – DISTANCE RELATIONS
As with Hubble’s Cepheid paper no. 5 before and his space distribution paper to come five years in the future, Hubble’s discovery paper of the expansion was written so convincingly that it was believed almost immediately. Despite its astonishing content and its few data points, Hubble must have been quite certain of the result. In the paper immediately preceding Hubble’s, Humason had reported the very large red shift, far larger than any red shift known before. From this result, Hubble must have been certain that an important phenomenon was at hand which would be useful in future.
On Mount Wilson, Hubble made all his best possible efforts to confirm and to extend the astounding possibility that the universe expands. In 1930, Humason had obtained red shifts of galaxies in clusters whose ‘velocities’ were as high as 20,000 km/s. Hubble and Humason showed in the most important paper beyond doubt : (a) the existence of the effect (b) that it was linear with distance, and (c) that the brightest members of clusters are predominantly E galaxies.
After showing the generality of the phenomenon, the work was extended to field galaxies. By 1936, the work had been completed as far as it was to be done with the Mount Wilson reflector, reaching red shifts for Ursa Major No. 2 cluster. He summarized the work finally in his Darwin Memorial Lecture.
HUBBLE’S INFLUENCE ON MODERN ASTRONOMICAL CULTURE THROUGH OTHER WORKS
(1) Hubble solved the problem of the source of radiation and the nature of the spectra of diffuse nebulae recognizing the difference between reflection and emission nebulae, and proving that the source of radiation of reflection nebulae is an associated star. His work was given an elegant appreciation by Greenstein.
(2) Hubble measured accurately for the first time, the surface brightness profiles of external galaxies providing the basic model from which modifications and extensions of the profile laws would be derived later by others.
(3) Hubble began the detailed study of the stellar content of the nearby galaxies. Besides the identification and measurements of Cepheids and very bright irregular variables in members of the Local Group, he made the unprecedented identification of the Global clusters in M31, starting a scientific activity that occupies many present-day astronomers.
(4) He discussed the sense of rotation of the spiral arms in individual galaxies.
(5) In one of the most important paper, Hubble and Baade found the nature of the Sculptor and Fornax dwarf E galaxies – which had been announced by Shapely in 1938.
HUBBLE’S LAW
Astronomers had observed for many years that light emitting from the nebulae was moving towards the red band of the color spectrum. In physical terms it was known as red shifts in the color spectrum of the light emitting nebulae. To study and analyze this effect in detail, Hubble attached a sensitive spectrometer to his telescope and showed that this red shift was caused by the Doppler Effect : the motion away from the observer caused the light to have a longer wavelength, therefore appearing more red.
Using his data, Hubble defined a straight line fit between the data points showing that the red shift was proportional to the distance. Hubble’s Law states that the galaxy’s recessional velocity (v) is proportional to its distance from Earth. That is : v = Hr where H is a constant of proportionality, named Hubble’s Constant.
Hubble’s researches and works successfully provided the first evidence for the Big Bang theory, which describes the origin and evolution of the universe. He discovered the fundamentals of cosmos, and while doing so founded the new science of cosmology.
HUBBLE CONSTANT
There is quite an uncertainty in the exact value of the Hubble’s constant, but it is generally believed to be between 50 and 100 kilometers per second for every megaparsec in distance. Essentially, the Hubble’s constant sets the rate at which the universe is expanding.
HUBBLE FLOW
The continuous movement of the galaxies away from us caused by the expansion of the universe is called Hubble Flow.
LUNAR CRATER HUBBLE
The Lunar Crater Hubble is a circular depression 80 kilometers in diameter located on the moon at latitude 22.1 N, longitude 86.9 E. In 1946, it was adopted by the International Astronomical Union General Assembly and named in his honor.
HUBBLE’S SIGNIFICANT DISCOVERIES
In astronomical community, his name is attached to a long string of significant discoveries – Hubble’s Zone of Avoidance, the Hubble Galaxy Type, the Hubble Sequence, the Hubble Luminosity Law for Reflection Nebulae, the Hubble Luminosity Profile for E galaxies, the Hubble Constant, the Hubble Time, the Hubble Diagram, the Hubble Red Shift Distance Relation, the Hubble Radius for the Universe, and now the Hubble Space Telescope.
1924
Edwin Hubble found Cepheid variables in the Andromeda and other nebulae.
1925
Created the first useful scheme for classifying galaxies.
1926
Hubble proposed the system of classifying galaxies according to their apparent shape and structure.
1927
Hubble discovered that the external galaxies are apparently receding from the Milky Way.
1929
Hubble established that the radial velocities of the galaxies increase proportionately with their distance.
1931
Hubble and Humason determine the brightness of Cepheid variable starts in the local group of galaxies and other stars.
1935
Hubble while studying the red shifts of nebula, estimated them to be 240 million light years away.
HUBBLE’S REVIEW WITH BBC
Before the Hale 200-inch reflecting telescope was completed at Mount Palomar, once in a BBC interview, Edwin Hubble was asked, "What do you expect to find with the 200-inch ?" Hubble replied, "We hope to find something we hadn’t expected."
HUBBLE’S SPACE TELESCOPE
When we usually speak of telescope, Galileo’s name frequently surfaces, for he popularized the instrument for astronomical purposes. All the incredible discoveries of Hubble are discussed in this biography, particularly his proof of the very existence of galaxies outside the Milky Way. His discoveries implicate that the leaps in astronomy’s understanding of the universe made by Hubble’s work are comparable to those made by the studies of Galileo or Copernicus.
The earth’s atmosphere obscures ground based telescopes by absorbing and distorting the light. Therefore, the United States Congress authorized the construction of a sophisticated optical observatory to be placed in earth’s orbit. The Hubble’s Space Telescope was constructed by NASA and went into orbit, about 600 kilometers above the earth on April 25, 1990. It consists of two solar panels to supply power, a 2.4 meter primary mirror, a smaller secondary mirror, and various recording instruments that can detect visible, ultraviolet, and infrared light, with far more accuracy than any ground-based telescopes with the same specifications.
Hubble’s variable nebulae is 25,000 light years away from earth. It is a fan shaped cloud of gas and dust, which is illuminated by R Monocerotis, the bright star at the bottom end of the nebulae. Dense condensations of dust near the stars cast shadows out into the nebulae and as they move, the illumination changes, causing the variations first noted by Hubble. The star itself is thought to be 10 times the mass of the sun, and only 3,00,000 years old.
Today the best telescope we have, not on earth, but a satellite observatory orbiting our planet carries Hubble’s name. This is because NASA named its largest, most complex and capable orbiting telescope in his honor and dedicated his namesake to discovering the true age and size of the universe.
MISSION STATISTICS
LAUNCH : April 24, 1990 from Space Shuttle Discovery (STS-31)
DEPLOYMENT : April 25, 1990
MISSION DURATION : Up to 20 Years
1st Servicing Mission : December 1993
2nd Servicing Mission : February 1997
LENGTH : 43.5 ft (13.2 m)
WEIGHT : 24,500 lb. (11,110 kg)
MAXIMUM DIAMETER : 14 ft (4.2 m)
Hubble is nearly the size of a large school bus – but it can fit inside a space shuttle cargo bay.
• The universe is unforcing as it should.
• Equipped with his five senses, man explores the universe around him and calls the adventure science.
• Thus, the explorations of space end on a note of uncertainty. And necessarily so. We are, by definition, in the very center of the observable region. We know our immediate neighborhood rather intimately. With increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary – the utmost limits of our telescopes. There we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial.
• The search will continue. Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.
• Every action of our lives touches on some chord that will vibrate in eternity.
• It was not that the galaxies were expanding to fill empty space as that space itself was stretching outwards, uniformly, in all directions.
• No one, should go into astronomy without a genuine call, and the only way to test a call is by having another calling to be called away from.
• The history of astronomy is a history of receding horizons.
• We find them smaller and fainter, in constantly increasing numbers, and we know that we are reaching into space, farther and farther, until, with the faintest nebulae that can be detected with the greatest telescopes, we arrive at the frontier of the known universe.
• The field is new, but it offers rather definite prospects not only of testing the form of the velocity – distance relation beyond the reach of the spectrograph, but even of critically testing the very interpretation and prefers the colorless term ‘apparent velocity’.
• Hubble was awarded a Rhodes Scholarship to study at the Oxford University in England, where he earned a law degree in 1912.
• Hubble was elected Honorary Fellow of Queen’s College, Oxford in recognition of his notable contributions to astronomy is 1948.
• Edwin Hubble was born in 1889 and died in 1953. Near the peak of his scientific career the 200-inch telescope was dedicated. Hubble was present at the dedication of the observatory commemorated with a stamp.
• Harlow Shapely, who lived till 1972, ultimately acknowledged in an interview that "Hubble was an excellent observer, better than I."
• NASA named the world’s first space-based optical telescope after American astronomer Edwin P Hubble in 1990.
• In April 2000, the United States Postal Services issued a set of five stamps commemorating discoveries from the Hubble Space Telescope.
• The May 2000 issue of Sky and Telescope has an article "Beyond the Hubble Sequence", by G D Bothun, which discusses the work of Hubble in a more modern context. It is interesting to note that Hubble’s classification of galaxies has been with astronomers for over 70 years and will remain so for long time to come.
