Edwin Powell Hubble was an American observational cosmologist and father of modern cosmology whose radical discoveries changed our ideas about the universe. Hubble provided the first convincing evidence of the existence of external galaxies and of expansion of the universe. Before the discovery, the Milky Way galaxy was considered as the only galaxy in the universe and the concept of static universe was also predominant.
Early Life and Education
Hubble was born in Marshfield, Missouri on November 20, 1889. Soon after his birth, his family moved to Wheaton, Illinois where he attended Wheaton High School from 1902 to 1906. In 1906, he received a scholarship to University of Chicago, where he studied astronomy, mathematics, and philosophy before graduating in 1910. Apart from being good in studies, he was also a fine athlete. He was part of University of Chicago championship basketball team and also practiced boxing at times.
For the next three years he went to England as a Rhodes Scholar and studied law and Spanish at Queen’s College, Oxford. He moved back to U.S. in 1913 and taught mathematics, physics, and Spanish at a high school in New Albany, Indiana. He also coached the school’s basketball team. He practiced law in Louisville, Kentucky but soon he left it for his passion of astronomy, returning to University of Chicago in 1914. There he studied astronomy at Yerkes Observatory in Wisconsin and received his doctorate in 1917.
Edwin Hubble also volunteered during the war after completing his doctorate and even rose to the rank of a lieutenant colonel. He was then offered a staff position by George Ellery Hale at Mount Wilson Observatory, California. In 1919, he accepted Hale’s offer when he returned to U.S. after World War I.
Hubble’s arrival at Mount Wilson coincided with the completion of construction of 2.5-meter Hooker Telescope at the observatory. At that time, it was the world’s most powerful telescope that allowed Hubble to look into the sky with greater details. During the first two decades of 20th century, it was thought that Milky Way is the only galaxy in universe and all the stars, planets and nebulae were contained within that galaxy.
Hubble’s Discovery of External Galaxies
When Hubble joined Mount Wilson Observatory, the astronomers were trying to measure distances in space with the help of Cepheid variable star. Cepheid variable stars brighten and dim periodically and by measuring their brightness, their distance from earth can be calculated. After years of observation on nebulae, in 1923 Hubble made a momentous find. He found a Cepheid variable in outer area of a spiral nebula called Andromeda nebula and calculated the star’s actual brightness using period-luminosity relationship, an empirical relationship between the periods of light variation for Cepheid and their absolute brightness, from which he deduced that the nebula was far too distant to be a part of Milky Way. Almost within a year, he had gathered enough data from Cepheid variables and other such ‘distance indicators’ to convince other astronomers that the outer regions of the Andromeda nebula consisted of gigantic collections of stars and that the nebula was indeed another galaxy.
Hubble’s discovery ended a long dispute on the existence of external galaxies. His success was due in part to his skilled deployment of very powerful telescopes of his time. He then studied other galaxies in more detail and proposed a system to classify them into different groups depending on their shapes, this system is known as Hubble tuning fork diagram or Hubble sequence.
Hubble’s next big discovery was to show that the universe is expanding. In the late nineteen twenties, Hubble studied the movement of galaxies along with his assistant Milton Humason. He found that greater the distance between any two galaxies, the greater their relative speed of separation. He used the concept of redshift of galaxies, i.e., if an object is moving away from an observer, the visible light reflected or emitted by the object will move towards the red end of the electromagnetic spectrum. Based on his observations, in 1929, he stated his famous “redshift distance law of galaxies”, better known as Hubble’s Law which states that the more distant a galaxy, the greater the redshift.
The mathematical equation representing Hubble’s Law is:
Where v represents velocity, d is distance and is known as Hubble Constant. Hubble constant is one of the most important numbers in cosmology, indicating the rate at which universe is expanding.
Early research on the movement of galaxies was done by Vesto M. Silpher who observed that many of the spiral nebulae were moving away from us but he lacked enough resources to prove his observations. This discovery of Hubble also provided the observational support for the expanding universe theory which had been proposed by Alexander Friedmann in 1922 and George Lemaitre in 1927.
From 1942 to 1946, during the World War II, he served US Army as a head of ballistics at the Aberdeen Proving Ground. He also contributed in the design and construction of 200-inch Hale telescope at Palomar Observatory in California. In 1949, on the completion of Hale Telescope, Hubble was the first to use it. To admire his contributions in astronomy and during the war, he was awarded various medals and awards including Bruce Medal in 1938, Gold Medal of the Royal Astronomical Society in 1946 and Medal of Merit for outstanding contributions to ballistic research in 1946.
Hubble Space Telescope
In April 1990, Hubble Space Telescope, named after Edwin Hubble was launched into orbit. It is the first major optical telescope to be placed in space. One of the major purposes of Hubble Telescope was to figure out the value of Hubble Constant. Since then the telescope is helping us to explore the Universe and has made many major discoveries, from the acceleration of the Universe to the existence of dark energy and dark matter.
Hubble’s Last Days
On September 28, 1953 Hubble died of a blood clot in his brain, in San Marino, California. Before his death, he was planning to spend some nights with his telescope to gaze over the horizon once again. He remained at Mount Wilson Observatory till his death. Hubble gave birth to modern cosmology and his work transformed our understanding of the universe.
From our home on Earth, we look out in the distances and strive to imagine the sort of world into which we are born.