Humanity’s Most Mind-Bending Cosmic Discovery in the 1920s Happened at This Remote California Mountain

Mount Wilson Observatory

Before Edwin Hubble, most scientists believed the universe was a fixed, unchanging place.

Then came the 1920s at Mount Wilson Observatory, where Hubble’s careful observations through the world’s largest telescope revealed something incredible.

Here’s how this remote California observatory became ground zero for modern cosmology.

Mount Wilson Observatory

George Ellery Hale built Mount Wilson Observatory in 1904 with money from the Carnegie Institution of Washington. He picked a spot 5,000 feet up in the San Gabriel Mountains near Los Angeles where the air was clear for stargazing.

The observatory’s crown jewel, the 100-inch Hooker telescope, was finished in 1917. Businessman John Hooker paid $45,000 for the mirror. This massive instrument remained the world’s largest telescope for over 30 years.

Its unprecedented light-gathering power let astronomers see deeper into space than ever before.ution. He picked a spot 5,000 feet up in the San Gabriel Mountains near Los Angeles for its clear skies.

Edwin Hubble Arrives at Mount Wilson

Edwin Hubble joined Mount Wilson in 1919 after serving in World War I. Born in Missouri, he had studied at the University of Chicago and Oxford before the war interrupted his career.

His timing was perfect. The brand-new Hooker telescope was ready for use, and Hubble wanted to study mysterious spiral nebulae – fuzzy patches of light in the night sky.

Back then, most astronomers, including Mount Wilson’s Harlow Shapley, believed these nebulae were inside our Milky Way galaxy, which they thought made up the entire universe.

Hubble set out to test this idea.

The Andromeda Discovery

On October 5-6, 1923, Hubble took a photograph of the Andromeda Nebula. Looking at the plate labeled H335H, he spotted what he first thought was a nova star.

Comparing it with other images, he realized it was actually a Cepheid variable star – a star that brightens and dims in a regular pattern. He crossed out “N” and excitedly wrote “VAR!” on the plate.

This was crucial because Cepheid variables act like cosmic yardsticks. By measuring this star’s brightness cycle, Hubble calculated Andromeda was 900,000 light-years away – far outside our galaxy.

Hubble had found the first confirmed galaxy beyond our own.

Redefining the Universe

Throughout 1924, Hubble photographed more nebulae and found additional Cepheid variables in them. Each discovery confirmed these objects were separate galaxies far beyond our Milky Way.

The New York Times announced his findings in November 1924, and Hubble presented his evidence to fellow astronomers on New Year’s Day, 1925.

His work completely transformed our view of the cosmos. What was once thought to be a single galaxy became a universe filled with countless galaxies.

Hubble organized these galaxies into a classification system based on their shapes – elliptical, spiral, or irregular – that astronomers still use today.

Measuring the Redshift

Hubble next investigated how these galaxies moved relative to Earth by studying their light patterns. He built on work by Vesto Slipher, who had shown most galaxies display “redshift” – their light waves stretched toward the red end of the spectrum.

This redshift works like a train whistle dropping in pitch as it moves away. When a light source moves away from us, its wavelengths stretch out, shifting toward red.

Slipher’s data suggested most galaxies were moving away from Earth. Hubble realized if he combined redshift measurements with his distance calculations, he might discover how galaxies move through space.

This was his next breakthrough.

Milton Humason’s Crucial Role

Milton Humason took an unusual path to astronomy. He started as a mule driver hauling supplies up Mount Wilson, then became a janitor at the observatory before joining the scientific staff in 1919.

Despite having no formal education, Humason developed exceptional skill at operating the telescope and capturing spectra from faint galaxies. He would spend entire nights keeping stars centered in the telescope’s view for eight-hour exposures.

Between 1929 and 1936, Hubble and Humason measured nearly 140 galaxies together. Humason’s technical expertise perfectly complemented Hubble’s theoretical mind.

Without this partnership, the expanding universe might have remained undiscovered.

The 1929 Breakthrough

In 1929, Hubble published his groundbreaking paper showing the relationship between galaxy distances and speeds. His simple graph revealed a clear pattern: the farther a galaxy was from Earth, the faster it moved away.

Using data from 24 galaxies, Hubble showed this relationship was consistent. For each additional million light-years of distance, a galaxy’s speed increased by about 500 kilometers per second.

This pattern became known as Hubble’s Law. It provided the first solid evidence that the universe is expanding in all directions, like a balloon inflating.

This seven-page paper completely changed how we understand the cosmos.

The Hubble Constant

The mathematical relationship Hubble found is written as v = H₀d. The velocity (v) of a galaxy equals its distance (d) multiplied by a number called the Hubble constant (H₀).

This constant describes how fast the universe expands. Hubble’s 1929 calculation put this value at about 500 kilometers per second per megaparsec.

The Hubble constant works like a cosmic ruler. Once measured, astronomers can determine any galaxy’s distance just by checking its redshift.

It also tells us the universe’s age. The inverse of the Hubble constant roughly equals how long the universe has been expanding since the Big Bang.

Scientific Implications of an Expanding Universe

Hubble’s discovery aligned perfectly with Albert Einstein’s theory of relativity. Einstein’s equations had actually predicted an expanding universe, but he added an extra term to keep the universe static because he thought that made more sense.

A Belgian priest and mathematician named Georges Lemaître had already mathematically predicted in 1927 what Hubble would observe two years later.

When Einstein learned of Hubble’s findings, he called his modification his “biggest blunder.” The evidence now supported his original equations.

The expanding universe suggested everything started from a single point – the foundation of the Big Bang theory.

Extending the Research

Hubble and Humason continued their work through the 1930s, measuring hundreds more galaxies. Each new observation strengthened their original findings.

For extremely distant galaxies where Cepheid variables were too faint to see, Hubble developed new methods. He used the brightest stars in these galaxies as alternative distance markers.

By 1936, they had measured 140 galaxies. Some distant ones moved away at thousands of kilometers per second – a significant fraction of light speed.

Hubble kept refining these measurements at Mount Wilson until his death in 1953, creating methods astronomers still use today.

Legacy and Refinement

In 1952, astronomer Walter Baade discovered there are actually two types of Cepheid variables with different brightness patterns. This meant Hubble’s distance calculations needed adjustment.

Baade’s correction doubled the estimated distances to galaxies and set the universe’s age at about 14 billion years – older and larger than Hubble had calculated.

The value of the Hubble constant has been debated for decades. Modern measurements place it around 74 km/s/Mpc, much lower than Hubble’s original figure.

The Hubble Space Telescope, launched in 1990, continues his work. His discoveries sparked ongoing research into cosmic expansion, dark energy, and the universe’s ultimate fate.

Visiting Mount Wilson Observatory

Mount Wilson Observatory sits in the San Gabriel Mountains near Los Angeles. The 100-inch Hooker telescope that revealed the expanding universe remains in its original dome.

The observatory offers public viewing sessions and allows groups to rent the historic telescope.

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