The American astronomer Edwin Hubble, whose 135th birthday is celebrated on 20 November, is most commonly associated with the expansion of the Universe. In 1925, he proved that space is not limited to our galaxy. Later, he discovered the law according to which star systems fly apart in space the faster they are located the further away from each other.
How large is the Universe?
On 1 January 1925, the American Astronomical Society held a meeting. It considered a report by the little-known astronomer Edwin Hubble. It was devoted to determining the distance to the cepheid he had observed in the Andromeda Nebula.
Cepheids are giant variable stars that decrease in size and then increase again at regular intervals. At the same time, their luminosity is directly related to the pulsation period. Therefore, observing them, you can always determine the absolute magnitude of the star, and from it calculate the distance to the object.
At the time of Hubble’s report, it was a new method, but there was nothing sensational about it. But the number named by the astronomer really impressed everyone – 2 million light years. This meant that the entire Andromeda Nebula lies far beyond the Milky Way, and is a star system that is as large as our own Galaxy.
Thus, Hubble put an end to a great debate that had been going on between astronomers much more famous than him for several years. It’s hard to believe, but 100 years ago, astronomers didn’t know whether the Milky Way was the only galaxy in the universe, measuring just 300,000 light-years across, or whether it was actually much larger.
At the time of the discovery that made him famous, Hubble is usually described as a young astronomer who had just begun his journey that led him to discover the vast world of galaxies beyond the Milky Way. However, at the time of the presentation, he was already 35 years old. So, what did he do before he became an expander of the Universe?
Childhood and youth
20 November 2024 marks the 135th anniversary of Edwin Hubble’s birth. He was born in Mississippi into the family of a poor insurance agent and spent his entire childhood in the American outback. At school, Edwin was known primarily as an athlete. He played football, baseball, and ran track. It would seem that he was an ordinary guy. However, Hubble had excellent grades in all his subjects.
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So, he had no trouble getting into the University of Chicago. His studies there were quite peculiar. On the one hand, Hubble continued to play sports and was quite popular. But then again, at the behest of his father, who had been earning money through hard work all his life, he persistently studied law in order to, as they say, ‘go out into the world’. And somewhere between all this, he is also taking courses in physics and mathematics, which he has been fond of since childhood.
Edwin Hubble received his bachelor’s degree in 1910 at the age of 21. He went to Europe, to King’s College, to continue his studies there under a special programme. Interestingly, it was again related to law. You would think, what about astronomy?
However, in 1913, Hubble’s father dies and he has to return from Europe to take care of his family, which is left without money. Edwin had to teach Spanish, physics, mathematics and even coach a volleyball team at school. He also had to work in his main specialty, which is law.
The path to astronomy
After about a year of teaching, Hubble managed to stabilize his family’s financial situation. He was finally able to quit studying law, which he had been doing solely at the behest of his father, and finally devote himself to what he had always been interested in astronomy. At the age of 25, he returned to his native University of Chicago, but this time to the Yerkes Observatory at the same university.
Here he is working on his own dissertation on photographic research of distant nebulae. The very ones that have been the subject of a controversy: whether they are inside the Milky Way or far beyond it.
However, Hubble did not manage to finish the work on it. In 1917, the United States entered the First World War and he found himself in the army, where he was promoted to the rank of major. It would seem that he was once again extremely far from astronomy.
However, Hubble’s life is full of strange twists and turns. His battalion is sent to Europe but kept in reserve. So, he never gets to the front line. The war ended and Edwin returned to his scientific work.
And then he got his lucky break. The Mount Wilson Observatory had just completed the construction of the largest telescope at the time, with a mirror diameter of 254 cm. And Hubble was invited to work with it. In 1921, he defended his dissertation and delved into the study of cepheids, which ended with the discovery that made him famous all over the world.
The conclusion that the Andromeda Nebula is not part of the Milky Way is an interesting story. Usually, the date of discovery is the publication of research results in a scientific journal.
However, Hubble first published the results in a newspaper in the autumn of 1924. They looked too dubious from the point of view of many American astronomers. A report followed, but he did not publish an article with the research until 1929.
Extragalactic astronomy
After his discovery, Hubble became world famous, and new horizons opened up for him. Beyond the Milky Way lay a vast world filled with tens of millions of galaxies of various shapes. And it was Hubble who created the first classification of them.
Meanwhile, the main work of the scientist focused on determining the distances to galaxies and their speeds. Back when Hubble was a schoolteacher, astronomer Vesto Slipher noticed that the spectra of many nebulae were heavily skewed towards the red. A few years later, an explanation was found – they were moving away from us at a high speed.
Hubble compared his estimates of the distance to these star systems with their redshift, and made another surprising discovery. Their velocities are generally proportional to their distances. This pattern was called Hubble’s law, and the value that related distance to velocity was called Hubble’s constant.
They are the basis of modern ideas about the Big Bang and the time when it occurred. However, Hubble himself was much more skeptical. The fact is that due to the insufficient study of cepheids, as well as due to the absorption of light from them by dust, at that time he estimated the distance to many galaxies to be 7 times less than it actually was. This led to the conclusion that the Big Bang happened only 2 billion years ago, which was clearly nonsense.
In addition, Hubble was very concerned about the fact that galaxies were too evenly distributed in space. After another large-scale observation confirmed this fact in 1941, he expressed the opinion that such a picture could not be observed as a result of the explosion. It was only later that scientists found that his first conclusion was absolutely correct, and his later doubts were not.
Edwin Hubble did a lot to popularize astronomy. He fought all his life to ensure that it was recognized as a part of physics and that scientists who study the stars could be awarded the Nobel Prize, just like physicists.
Although he did not receive the most prestigious scientific award, the Prize Committee eventually began to give it to astronomers. But Hubble was honored in another way. The most famous space telescope is named after him. A crater on the Moon and an asteroid are also named after him.
