Expanding Knowledge, Expanding Universe: How Mount Wilson Observatory and Hubble Changed Our View of the Universe

Our home, the Milky Way, is just one of trillions of galaxies in the universe. This is common knowledge today, but up until the 1920s, scientists believed that the Milky Way itself, accounted for the sum total of the universe.

It's thanks to the Mount Wilson Observatory, Edwin Hubble, and calculations provided by "human computer" Henrietta Swan Leavitt that we are aware of just how small of a chunk of space real estate we're renting. To take a look at what led to Hubble's famous discovery, we must peer, as telescopes do, into the past.

A History of Mount Wilson Observatory and its founder George Ellery Hale

In 1904, astronomer George Ellery Hale founded the Mount Wilson Observatory in the San Gabriel Mountains outside of Los Angeles with funding from the Carnegie Institution of Washington. In addition to being the founder of the Mount Wilson Observatory, Hale is also regarded as one of the pioneers in creating the field of astrophysics. Prior to his tenure at Mount Wilson, Hale founded The Astrophysical Journal in 1895, which is still in publication today. In 1899, Hale created the American Astronomical Society and the International Astronomical Union in 1904 – the same year he founded Mount Wilson.

The facility was originally dubbed the Mount Wilson Solar Observatory due to Hale's interests in solar astronomy. Hale, a longtime proponent of observatories (He built his first one at his family home at age 20.) and sun studies (He invented the spectroheliograph at MIT.), established Mount Wilson originally to aid in his studies of the sun. Hale bought Mount Wilson's original telescope, the Snow telescope, from the Yerkes Observatory in Wisconsin. In addition to the Snow telescope, the 60-foot solar telescope was completed in 1908 and the 150-foot solar telescope in 1910. Note that 'feet,' in this usage, refers to the focal length of the telescopes rather than the height of their towers.

The three solar telescopes are still present at Mount Wilson today. However, the 60-foot solar telescope is the only one of the three still used for solar research. The Department of Physics and Astronomy at USC uses it for helioseismology research, a field that investigates the internal structures of the sun.

The region of the Milky Way galaxy in the Eagle constellation taken by NASA Herschel | JPL, ESA/Hi-GAL Consortium

The arrival of 100-inch Hooker telescope

The addition of the 100-inch Hooker telescope to Mount Wilson in 1919 was a gamechanger for the observatory. With the arrival of the 100-inch, the observatory in today's terms 'rebranded.' The 'solar' was dropped from the name as more focus was placed on observing and photographing visible nighttime sky phenomena such as nebulae and individual stars.

The measure of 100 inches pertains to the diameter of the mirror used in the telescope. From when it was fully assembled in 1917 to 1949, the Hooker telescope was the largest in the world. Not only that, but this telescope would turn out to be the tool that would photograph the Andromeda galaxy and change our understanding of our place in the cosmos.

There are quite a few reasons why the 100-inch was and is regarded as unusual and quite special. First of all, it was not easy to build. Hale ordered the huge mirror from Saint Gobain Glass in France in 1906. In 1908, the 4.5-ton mirror left France and crossed the ocean to New Jersey. The disk then traveled by train to California and finally up the primitive mountain road with help from early model Mack trucks. However, when Hale inspected it, he initially ruled it unusable due to defects in the glass. In 1913, the mirror was re-examined and, thankfully, was deemed usable. The mirror itself, a $45,000 investment, was paid for by businessman John Hooker, the telescope's namesake.

Click right or left below to see more of the 100-inch telescope and its journey:

Transporting the 100-inch mirror to Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

Cleaning the mirror for the Hooker 100-inch telescope at Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

Mirror for the Hooker 100-inch reflecting telescope in its cell, Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

Hooker 100-inch reflecting telescope, Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

Secondary mirrors of the 100-inch and 60-inch telescopes. Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

Lower section of the Hooker 100-inch reflecting telescope, Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

Walter S. Adams, Edwin Powell Hubble and James Hopwood Jeans at the control panel of the Mount Wilson Observatory | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

In its hundred-plus year history, the Hooker telescope has been used by scores of scientists including, of course, Edwin Powell Hubble.

Before we look at Hubble's discoveries made by looking through the Hooker telescope, it's interesting to note that you, too, can use the 100-inch to view the cosmos. Mount Wilson makes the telescope available for groups to rent, and the observatory occasionally offers ticketed events to the public. Imagine looking out into the vastness of space using the same instrument that changed our understanding of it!

Edwin Powell Hubble and his discoveries

Edwin Hubble came to Mount Wilson in 1919 and was hired as a junior astronomer. Most other scientists, including those who worked at Mount Wilson, believed that all of the nebulae they were looking at through the 100-inch telescope existed in our galaxy. To test his theory that some stars might be farther away, in their own galaxies, Hubble used the Hooker telescope to take multiple photos of the same set of what were then regarded as nebulae. 

The photograph that would change everything was of what we now know as the Andromeda Galaxy. The galaxy is 2.5 million light-years away from Earth, and in October of 1923, Hubble noticed something particular in his comparison photos. Something in it was brighter than was expected. Over several months, Hubble calculated that the brightness of one particular star in his photograph had intensified.

Edwin Powell Hubble seated at the Newtonian focus of the 100-inch telescope on Mount Wilson  | Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

The calculations that Hubble used were based in part on the work of Henrietta Swan Leavitt, a "human computer," an individual who performed a series of complicated calculations. Leavitt figured out the mathematical relationship between period and brightness in certain types of stars, meaning that one can determine things like how far away a star is by observing its brightness over a period of time. Hubble's observations combined with Leavitt's Law allowed Hubble to prove that the Andromeda galaxy exists in space too far away to be included in the Milky Way.

As if proving that the universe is made up of more than just our galaxy, Hubble's research (based on Leavitt's mathematics) also proved that the universe is expanding, thus supporting the Big Bang theory. The theory states, more or less, that the universe started as a very small, dense single point and then approximately 13.8 billion years ago exploded very, very quickly and has been expanding outward ever since.

We now accept the Big Bang theory as scientific gospel, and our understanding of the universe and how it began would not have been possible in the same way without Mount Wilson Observatory's 100-inch Hooker telescope, Edwin Hubble's theory and photographic evidence, and the mathematical laws proven by Henrietta Swan Leavitt. Scientific discoveries are not made in a vacuum, and it's important to remember that all science is based on previous science. Isaac Newton said it best, "If I have seen further, it is by standing on the shoulders of giants."

In the case of Hubble's discoveries made at Mount Wilson, the giants are all those who came before him and paved the way for astrophysics as a field as well as those individuals who proved mathematical theories that the current research was based on. As Hubble made discoveries that made future discoveries possible – and so on­ – it's fitting that he is immortalized in his own telescope, which has made its own discoveries. In telescope terms, perhaps the current orbiting Hubble Space Telescope 'stands on the shoulders' of its predecessors including Mount Wilson's 100-inch Hooker telescope.

Whichever way you prefer to look at it, the fascinating fact remains that our current understanding of the universe is thanks to the work performed at Mount Wilson, an observatory which is located just twenty-five miles from the heart of Los Angeles. In SoCal gridlock terms, that might seem like light-years of distance ­— but in a galaxy of trillions, a trip to Mount Wilson Observatory is just a hop, skip and a jump away.

To learn more about Mount Wilson's history, current projects including events, and details on visiting, visit the observatory's website.

Top Image: The spiral galaxy M100 observed with Hubble's Wide Field Camera 3 | NASA, ESA and Judy Schmidt