Chapter 1: The Shift in Cosmic Perspective

In 1923, the universe was perceived as a mere Milky Way galaxy. However, by 1924, our understanding expanded dramatically, revealing a cosmos of unimaginable complexity spanning billions of times larger than previously thought.

“In 1923, the universe had been the size of the Milky Way. By 1924, the space that surrounds us had been revealed to be billions of times bigger and home to almost unimaginable cosmic complexity.”

— Professor Jim Al-Khalili, Everything and Nothing: The Science of Empty Space 4k

Recently, NASA's Hubble Space Telescope made headlines by detecting the light from a star that shone during the universe's infancy, nearly 13 billion years ago. This ancient star, named Earendel, or “morning star” in Old English, is estimated to be fifty times more massive than our Sun, and its composition might differ significantly from that of contemporary stars.

While this discovery is indeed remarkable, it pales in comparison to the deeper narrative encapsulated in the name of the telescope itself: Hubble. Reflect for a moment on a transformative event in your own life—an instance that reshaped your worldview. Now, consider how magnified that transformation is when applied to the universe. This is the essence of Hubble's legacy.

You might be familiar with the name Edwin Hubble, but have you considered why NASA chose to honor him with a telescope? His story is far grander than that of an ancient star. It encapsulates the monumental shift from believing in a solitary galaxy to recognizing an infinite cosmos during the pivotal years of 1923 and 1924.

To grasp this narrative, we must first explore humanity's early attempts to decode the night sky.

Section 1.1: The Fixed Star Shell

In David Epstein's book Range, he describes a belief from the early 1600s that celestial bodies moved upon “pure crystalline spheres,” interlocking like clockwork. As Professor Al-Khalili points out, this notion created an illusion of a fixed star shell.

When a new star appeared in 1604, which turned out to be a supernova, it puzzled Johannes Kepler. His confusion deepened when he observed a comet traversing the sky, an occurrence that should have disrupted the supposed spheres. Lacking the concepts of gravity and modern telescopic technology, Kepler began to formulate the Laws of Planetary Motion, challenging the prevailing view that “souls” governed planetary movement by introducing the idea of a “force.”

Furthermore, Professor Al-Khalili highlights that Thomas Digges, influenced by an earlier supernova, realized that stars were not fixed. He envisioned a universe where stars were scattered throughout infinite space, moving away from the old model based on a sun-centered universe.

Section 1.2: The Milky Way and Dust Clouds

By the early 1800s, William Herschel, a musician with a passion for astronomy, began crafting telescopes equipped with polished metal mirrors, allowing him to observe fainter stars. In his studies, Herschel discovered the planet Uranus, gaining recognition and becoming England's court astronomer. With newfound resources, he set about cataloging the night sky.

Herschel documented what he called “island universes” and created a chart of what we now recognize as the Milky Way. Although he mistakenly placed our Sun at its center, his work was groundbreaking, especially considering that just a few centuries prior, scientists believed stars were fixed within a dome.

Despite these advancements, Professor Al-Khalili explains that astronomers noticed anomalies resembling clouds of dust. These were termed nebulae, and while some speculated they might represent other “island universes,” their distances remained elusive.

In 1883, Friedrich Bessel employed the Parallax method to measure a star's distance by observing it from two different angles. This technique, however, had limitations, only allowing measurements up to about 186 million miles, a mere fraction of the Milky Way's vastness. This led to confusion and debate within the scientific community.

Chapter 2: Unveiling Multiple Galaxies

As the early 20th century approached, two conflicting theories emerged regarding the nature of these dust clouds: either they were galaxies situated beyond the Milky Way, or they were merely part of our galaxy with nothing beyond.

This debate sounds naïve today, but at the time, the evidence—or lack thereof—supported both perspectives. It wasn't until Edwin Hubble turned the Hooker Telescope towards the Andromeda Nebula in 1923 that our understanding of the universe drastically changed.

Hubble observed what appeared to be “an elongated cloud of light,” but the advanced telescope revealed numerous stars. Utilizing a method developed by Henrietta Swan Leavitt, which measured distances based on the brightness of two pulsing stars, Hubble identified two such stars in both Andromeda and the Milky Way.

Upon measuring, Hubble discovered that the Andromeda star was far more distant than its Milky Way counterpart, providing definitive proof of another galaxy beyond our own. Furthermore, he calculated distances to stars in other nebulae, leading to the revelation that the universe was not limited to a single galaxy.

In just one year—between 1923 and 1924—the cosmos transformed from a singular entity to a boundless expanse of “island universes.” Consider the profound impact of this shift, as the world’s perception of the universe expanded infinitely within the span of a year.

The story of Edwin Hubble and the transformation from clouds of dust to galaxies epitomizes a monumental leap in human understanding.