Mount Wilson Observatory measured the size of the Universe, found the first evidence in favour of the Big Bang and this month celebrates its 100th birthday.
By Simon Singh
Science writer and broadcaster
Although astronomers are usually only interested in the latest, greatest and biggest telescope, they are all raising a glass and fondly reminiscing about the most important observatory of the 20th Century.
The observatory found the first evidence to support the Big Bang
It was 20 December, 1904, when George Ellery Hale first received news that the Carnegie Institution was prepared to fund his new observatory in the sum of $150,000.
This was a huge relief to Hale, who had already spent $27,000 of his own money financing his dream.
In fact, when the Carnegie Institution telephoned with the good news, Hale was at Martin's Camp, a small mountain resort about one mile below the summit of Mount Wilson, where he was planning the next stage of construction.
Mount Wilson, in the San Gabriel Mountains outside Los Angeles, would become home to the largest telescopes in the world for the next four decades.
Motor vehicles struggled to climb the steep road to the observatory, so hundreds of tonnes of material would have to be hauled to the mountaintop by mules in an effort to satisfy Hale's obsession with building telescopes.
Unfortunately, Hale's craving for perfection and the responsibility of managing big projects became self-destructive. The overwhelming stress resulted in periods of psychosis that ultimately forced him to spend months in a sanatorium in Maine.
His mental health deteriorated, particularly after he embarked on constructing the gigantic 100-inch (254cm) telescope.
As the basis for his mirror, Hale ordered a five-tonne glass disc from France, which the newspapers called the single most valuable piece of merchandise to cross the Atlantic.
George Ellery Hale and Andrew Carnegie
When it arrived, however, there was huge concern because the glass contained tiny air bubbles.
The telescope was eventually completed in 1917, and on the night of 1 November, Hale had the honour of being the first person to stare into the eyepiece. He was shocked to see Jupiter overlapped by six ghost planets!
Blame was immediately attributed to the bubbles in the glass, but calmer minds pointed out that the roof of the observatory had been open all day, so the mirror had been warmed and had possibly become distorted.
The astronomers disbanded until 3am to allow a cooling-off period. In the chill of the night, Hale's next view of the heavens was clearer than any previous observation in history.
The man who best exploited the power of the Mount Wilson telescopes was Edwin Hubble, whose first great discovery was to show in 1923 that the faint smudges that populated the heavens were in fact remote galaxies, each one consisting of billions of stars.
By measuring the distances to these galaxies, Hubble could estimate the scale of the Universe. Mount Wilson became famous and Hubble became a celebrity.
Tourists began to trek up to the mountaintop; the Hollywood glitterati would spend nights gazing at the sky and Hubble became a much sought after guest on the Los Angeles party circuit.
Edwin Hubble exploited the power of the Mount Wilson telescopes
In 1929, Hubble made an even greater discovery while working with his assistant Milton Humason, who had been promoted from mule driver to the most accomplished astronomical photographer in the world.
They used the 100-inch telescope to show that the other galaxies were moving away from our own Milky Way galaxy. Furthermore, the speeds of recession were consistent with what would be expected if the Universe had started with a Big Bang.
In other words, Hubble's observation supported the maverick theory that the Universe was created a finite time ago, as opposed to being an eternal cosmos.
As the years progressed, Mount Wilson became a site of pilgrimage for astronomers and cosmologists from around the world, all of them keen to see for themselves the incredible view of the cosmos provided by the giant telescopes.
But Mount Wilson's dominance began to diminish after the Second World War, when rival telescopes were constructed and the lights of an expanding Los Angeles began to pollute the skies above the San Gabriel Mountains.
Today's astronomers prefer to head to places such as Chile and Hawaii, where observatories are sited on even more remote and higher mountaintops.
Mount Wilson still conducts research, but its astronomers tend to use specialised instruments to study nearby stars (including the Sun) rather than stare at the distant galaxies through the giant telescopes, which still remain as monuments to the extraordinary discoveries that were made between the wars.
Tourists with an interest in the history of science drive up to the observatory, but the Hollywood stars no longer seem interested in the celestial stars.
However, the spirit of Edwin Hubble, George Ellery Hale and Mount Wilson lives on. For example, the Hubble Space Telescope, in name and ambition, proves that astronomers continue to push the limits of astronomy.
Earlier this month, the space Telescope showed that I Zwicky 18 is the youngest known galaxy.
This discovery elegantly linked present and past astronomy, as Fritz Zwicky first catalogued this galaxy back in the 1930s while working at Mount Wilson's base camp in Pasadena.
A telescope launched into orbit by a space shuttle might seem far removed from one hauled to a mountaintop by mules, but both are the result of an insatiable curiosity and a never-ending obsession about the Universe.
Simon Singh's latest book, Big Bang, is a history of cosmology.