Edwin Hubble was an American astronomer who played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology.
In the cover you can see a portrait of Edwin Hubble in 1931. Credit: Wikipedia. Photographer: Johan Hagemeyer.
Hubble is the man who made us see that our galaxy is not the only one in the Universe, but that there are thousands of galaxies and that the Universe is expanding.
The discovery of the expansion of the Universe led to the conclusion that there was an initial moment in which what we now call the Big Bang occurred.
Hubble’s name is most widely recognized for the Hubble Space Telescope, which was named in his honor.
Childhood and education of Hubble
Edwin Hubble was born in Marshfield, a city in the Missouri state, in the American Midwest, on November 20, 1889. He was son of a lawyer.
Hubble won a scholarship to study law at Oxford, where he stayed for three years.
However, he became more interested in astronomy and returned to the United States to study mathematics and astronomy at the University of Chicago.
He graduated in 1910.
Hubble started work at the Yerkes Observatory
In 1917, Hubble joined the Yerkes Observatory and obtained his doctorate in Physics there, in the same year 1917.
The Yerkes Observatory is an astronomical observatory installed in Williams Bay, Wisconsin, belonging to the University of Chicago.
It was inaugurated in May 1897, thanks to the fact that the astronomer George Hale had convinced his President of the need to build an astronomical observatory in the vicinity from their university.
The work was funded by magnate Charles Tyson Yerkes (1837-1905), whose body is buried at the base of the pylon of the main telescope mount.
Many of the most important astronomers, astrophysicists, and cosmologists of the 20th century worked at the Yerkes Observatory, including George Hale.
At the Yerkes Observatory, Hubble built a solid reputation as an intelligent and tireless researcher.
Mount Wilson Observatory
The Mount Wilson Observatory (near Los Angeles, California) was founded in 1904 by George Hale (1868-1938), an American astronomer who, like William Herschel, was always trying to build ever-larger telescopes.
In 1917, the Hooker telescope, the most powerful in the world in those years, with a 2.54 m diameter mirror, began operating on Mount Wilson.
George Hale knew of Hubble’s brilliant career as an astronomer, and immediately offered him a position at Mount Wilson.
But, Hubble could not join Mount Wilson until 1919, having had to serve in the First World War.
From the beginning, Hubble was the main user of the Hooker telescope.
The Hooker is a 60-inch (1.50 m) telescope, George Hale received, cast by Saint-Gobain in France, in 1896 as a gift from his father, William Hale.
From the beginning of his career at the Mount Wilson Observatory, Edward Hubble focused his attention on nebulae.
When Hubble arrived at Mount Wilson he was impressed by the skill and full dedication of Milton Humason, assistant telescope observations, and put him to work measuring the velocities of galaxies.
Together they made a highly effective team.
Humason published numerous research papers and discovered a comet named after him.
Cepheids are pulsating stars with periods ranging from several days to several months.
The brighter the star, the longer its period, so by measuring the period, a measure of the star’s luminosity can be obtained.
Once the luminosity of the star is known, it can be compared with the apparent brightness in the sky to obtain a measure of the distance to the star.
The Cepheids are thus like beacons that clearly indicate the distances at which they are.
Henrietta Leavitt was the American astronomer who discovered the Cepheids in 1904.
In 1925, Hubble found several Cepheids in the Andromeda nebula and found that they were about 900,000 light-years away.
He repeated the Cepheid measurements of other nebulae and also obtained distances greater than 100,000 light-years, which is the estimated size of the Milky Way.
Hubble deduced that such nebulae are outside the Milky Way, very far from it. He called them “extragalactic nebulae.”
Cepheids In those years it had been established that some nebulae were in the galaxy and that, basically, they were gas illuminated by stars located within.
But the Hubble findings showed that the Andromeda Nebula was much further away than the most remote known stars and that it was another world, another galaxy independent of ours.
In the following years, similar findings were repeated with many other nebulae, making it clear that our galaxy was one of a multitude of isolated galaxies, indicating that the Universe was much larger than previously believed.
Hubble then turned to classifying the galaxies. He identified spirals, ellipticals, lenticulars, and irregular ones.
In 1926, Hubble defined a sequence that is still known today as the ‘Hubble sequence’.
Hubble had transformed the image of the universe, but it did more still: in the half Century, since Huggins recorded the redshift of the spectrum of the star Sirius, numerous other redshifts and blueshifts had been recorded for various objects in the sky.
The expansion of the known universe
In 1929, Hubble published an analysis of the radial velocity of nebulae whose distance he had calculated.
It was about their speeds relative to Earth.
He claimed that although some extragalactic nebulae had spectra indicating that they were moving toward Earth, the vast majority showed redshifts.
This phenomenon could only be explained by assuming that these nebulae were moving away.
Even more surprising was the discovery that there is a direct relationship between the distance of a nebula and its speed of rebound.
That is, if Galaxy A is twice as far away as Galaxy B, the former is moving away from us at a speed that is twice the speed of the latter.
This linear relationship is known as Hubble’s Law.
Hubble concluded that the only consistent explanation was that, leaving aside a local group of nearby galaxies, all the extragalactic nebulae were moving away; and that the farther away they were, the faster they moved away.
This only made sense if the universe itself, including the space between galaxies, was expanding.
Honors given to Hubble
During his lifetime, Hubble received many medals and accolades.
He was a member of the Royal Astronomical Society, the American Astronomical Society, and many other scientific societies.
Due to the multiple discoveries of him, the Hubble space telescope is known throughout the world.
In 1953, at the age of 64, Hubble died suddenly of a heart attack in San Marino, California.
Shortly before his death, he had the opportunity to be the first to use the Hale telescope at the Monte Palomar Observatory.