The annals of science are filled with formally educated geniuses, but every so often, a figure emerges whose path to greatness is as unconventional as their contributions are profound. Milton Humason was such a figure, a man who began his association with the famed Mount Wilson Observatory not as a scholar, but as a mule driver and later a janitor. Yet, his innate curiosity, sharp intellect, and an almost uncanny skill for observation would eventually place him at the forefront of one of the 20th century’s most staggering astronomical discoveries: the expansion of the universe.
An Unlikely Start on a Cosmic Stage
Born in 1891, Milton Humason’s formal education was brief; he dropped out of school around the age of 14. Seeking adventure, he found his way to Mount Wilson in California, drawn not by the stars, but by the rugged work involved in the construction and maintenance of the burgeoning observatory. In those early days, supplies and equipment were often hauled up the steep mountain trails by mule teams. Humason, young and capable, took on the role of a mule skinner. Later, he worked as a janitor and then an electrician’s helper at the observatory complex. The rarefied air of the mountain, however, was not just thin; it was thick with intellectual fervor and the tantalizing mysteries of the cosmos being unraveled by the giant telescopes.
Humason, though lacking academic credentials, was far from unintelligent. He was observant, quick to learn, and deeply fascinated by the work unfolding around him. He would engage the astronomers in conversation, absorbing their discussions and gradually learning the intricacies of the instruments they used. His persistent interest and evident aptitude did not go unnoticed.
From the Ground Floor to the Telescope Dome
A pivotal moment came when one of the night assistants at the observatory resigned. Humason, by then a familiar and trusted presence, saw an opportunity. Encouraged by some of the astronomers who recognized his potential, he applied for the position. Despite his lack of formal qualifications, his practical skills, familiarity with the observatory’s workings, and a recommendation from influential figures like George Ellery Hale (though some accounts say Harlow Shapley played a key role) secured him the job in 1917. This was his entry point into the world of professional astronomy, not through a university, but through sheer grit and a keen mind.
As a night assistant, Humason proved to be exceptionally gifted. He possessed remarkable eyesight, unwavering patience, and an extraordinary ability to guide the telescopes with precision for hours on end – a critical skill for long-exposure astronomical photography and spectroscopy. He quickly mastered the complex operations of the 60-inch and, later, the monumental 100-inch Hooker telescope, which was then the largest in the world.
The Fateful Partnership with Edwin Hubble
In 1919, another astronomer arrived at Mount Wilson, one whose name would become inextricably linked with Humason’s: Edwin Hubble. Hubble was a charismatic and ambitious scientist, armed with a Ph.D. from the University of Chicago. He was focused on understanding the nature of the faint, fuzzy patches of light then known as “spiral nebulae.” Were they gas clouds within our own Milky Way galaxy, or were they unimaginably distant “island universes” – entire galaxies in their own right?
Hubble’s work first established the true nature of these nebulae as external galaxies. His next great quest was to determine their distances and their motions. This required obtaining detailed spectra of these incredibly faint and distant objects. While Hubble was the brilliant theorist and interpreter of data, he needed an observer with unparalleled skill and dedication to acquire that data. He found that person in Milton Humason.
The Master of Faint Light
Obtaining a usable spectrum from a remote galaxy was an immensely challenging task. The light from these objects was incredibly faint, spread out over a vast distance. The spectrographs of the era were inefficient by modern standards, requiring extremely long exposure times, sometimes spanning multiple nights, to capture enough photons to register on a photographic plate. During these exposures, the telescope had to be guided with pinpoint accuracy, keeping the faint image of the galaxy perfectly aligned on the narrow slit of the spectrograph.
This is where Humason excelled. He became legendary for his ability to sit for hours in the cold, dark observer’s cage high up in the telescope dome, meticulously guiding the massive instrument. He could detect and hold onto guide stars so faint that other observers couldn’t even see them. His patience was inexhaustible. He would often expose a single photographic plate for 30, 40, or even more than 70 hours, spread across several bitterly cold nights, to capture the ghostly spectral lines of a far-flung galaxy.
Milton Humason’s dedication to capturing the spectra of faint galaxies was extraordinary. He was known to endure frigid conditions in the observer’s cage of the 100-inch Hooker telescope for many hours at a time, often over consecutive nights, to secure a single precious spectrum. His longest recorded exposure for one galaxy exceeded 70 hours, a testament to his incredible patience and skill. This meticulous work was essential for the groundbreaking discoveries that followed.
These spectral lines held the key. If a galaxy was moving away from us, its light would be stretched, causing its characteristic spectral absorption lines (like those of calcium or hydrogen) to shift towards the red end of the spectrum – a phenomenon known as redshift. The amount of this redshift was directly proportional to the galaxy’s recession velocity.
Charting the Expanding Universe
Hubble had already begun to find evidence that the farther away a galaxy was, the faster it seemed to be receding. But to firmly establish this relationship – what would become known as Hubble’s Law – he needed many more data points, especially for very distant, and therefore very faint, galaxies. Humason was the engine room for this monumental effort.
Year after year, Humason painstakingly collected spectra. Each successful plate was a victory, providing another crucial piece of the cosmic puzzle. He would carefully measure the positions of the shifted spectral lines, calculate the redshift, and thereby determine the galaxy’s velocity. His results were consistently reliable, forming the bedrock of Hubble’s analysis.
Pushing Observational Limits
Humason’s observational prowess allowed him to push the boundaries of the observable universe further and further. In the early 1920s, typical measured velocities were a few hundred kilometers per second. By the late 1920s and early 1930s, thanks to Humason’s skill with the 100-inch telescope, he was clocking galaxies receding at thousands, and then tens of thousands, of kilometers per second. In 1929, using Humason’s data for relatively nearby galaxies, Hubble published his seminal paper proposing a linear relationship between distance and recession velocity. This was the first strong observational evidence for the expansion of the universe.
But the work didn’t stop there. Humason continued to hunt for ever more distant, fainter, and faster-receding galaxies. His measurements were crucial for extending Hubble’s Law and refining the value of the Hubble Constant. By the mid-1930s, Humason had measured redshifts corresponding to velocities exceeding 40,000 kilometers per second (over one-seventh the speed of light) for galaxies estimated to be hundreds of millions of light-years away. Each new record was a testament to his extraordinary ability and the power of the Mount Wilson instruments.
The Legacy of an Unassuming Observer
The life of an observational astronomer, especially in that era, was one of solitary dedication. Long, cold nights spent in near-total darkness, the quiet hum of the telescope drive, and the intense concentration required for guiding were Humason’s world. Yet, the thrill of discovery, the moment when a developed plate revealed the faint, shifted signature of a distant island universe, must have been an immense reward.
While Edwin Hubble became the celebrated public face of the expanding universe discovery, the contribution of Milton Humason was indispensable. Hubble himself acknowledged Humason’s critical role. Without Humason’s unparalleled observational skills, the data needed to formulate and confirm Hubble’s Law would have been much slower to accumulate, if it could have been gathered at all with such precision at that time.
An Enduring Inspiration
Milton Humason’s story is a powerful reminder that passion, dedication, and innate talent can often transcend the traditional pathways of academic achievement. He rose from a humble beginning to become one of the most skilled astronomical observers of his generation, playing a pivotal role in reshaping our understanding of the cosmos. He eventually gained the formal title of Astronomer and continued his work at Mount Wilson and Palomar Observatories (after the 200-inch Hale Telescope was completed) until his retirement in 1957. His meticulous measurements provided a robust observational foundation for modern cosmology, a legacy etched not in textbooks of theory, but in the hard-won photons captured from the edge of the visible universe.
