Milton Humason: The Man Behind the Hubble Law
Too frequently in science, people who make huge contributions are lost to history for various reasons. Some people assist important scientists in their work, providing critical ideas, while others may even have their work stolen from them. In this article, we will examine the case of the former, with Milton Humason. Here we will find an incredible example of a man who started with little and ended up shaping how we view the universe.
Working Up The Ladder
Humason’s astronomy career really began in 1902, when he moved to Los Angeles at the age of 12. Near there is Mt. Wilson, the location of the observatory that he would eventually work at for over 60 years. At 14, he decided to quit school and work at the mountain observatory, with the goal of living there. Clearly, the location was a fixation for the young man, and he started to help the staff build the telescopes that were built for them (Voller 52).
In fall of 1917 he got a job as a janitor there, mostly by virtue of his personality. The staff loved him and began to instruct him on some of the techniques of astrophotography. George Ellery Hale, the director and founder of the observatory, noticed that Humason had great potential and promoted him from janitor to night assistant. By 1922, 20 years after Humason first moved to LA, he was further promoted to the stellar spectroscopy department. This would forever shape his career, for it was at this time that Edwin Hubble was collecting data which would lead to the famous result of universal expansion (52, 54).
You see, in 1915 Einstein’s relativity was published. In it, one of the implications was a universe existing in 4 dimensions we call space-time. Friedmann was able to expound on this and in 1924 came up with an amazing result: the universe should be expanding. But theory is one thing, and evidence is another. Hubble came up with the evidence for the claim through his redshift study, which measured the stretching of light from the motion of an object. Hubble used Cepheid variables, which have a known period-luminosity relation that makes computing their distance easy. He had previously made use of them in his famous 1929 discovery of M31 aka the Andromeda galaxy, which he was able to show using the Cepheid variable star that the galaxy was outside the confines of our Milky Way. This then led to the “island universe” theory, which we know of as the concept of galaxies. But now, with more at his disposal, he was able to find compelling evidence for universal expansion (54).
Or so the story goes.
When Humason was promoted to the stellar spectroscopy department, he would take spectrum measurements of stars, breaking down the light they shined into wavelength components. Humason would verbally dictate the location of the object they were analyzing while assistant Allan Sardage would write it down. Now, supposedly around the time of this promotion of Humason, Shapely asked him to look at the photographic plates of M31 for any signs of a supernova or any new stars. Humason did just this and found some oddballs he suspected were Cepheid. Humason presented this to Shapely, who erased those marks because he felt they were clouds of gas with no stars in them. Imagine, if that incident actually did happen (for no evidence exists for the event) then Humason was potentially robbed of the chance to uncover the universe’s true nature. Hubble didn’t even start the work that would lead to that conclusion until 1923. We would be talking about the Humason Law instead of the Hubble Law! (Ibid)
So, the question begs: why didn’t Humason defend his findings? After all, he was gifted enough to be a member of the staff without a formal education, but this may have been considered a hindrance to some. Humason also looked up to Shapely as a mentor figure, so maybe out of respect Humason did nothing. Whatever the reason, Humason missed the opportunity. But that doesn’t mean the story with Hubble has ended (55).
Hubble and Humason at Mt. Wilson
At an IAU meeting in 1928, Hubble begins to think about Friedmann’s prediction of an expanding universe and specifically what those conditions would result in. Hubble wanted to find evidence for the expansion, and so his thoughts turned to what he had been studying for years: his “island universes.” He figured out that fainter objects would imply a faster receding velocity because of the Doppler effect stretching out the light. To prove this, Hubble needed data, which translated to lots of spectrums. Through word of mouth, Hubble heard about Humason and his work at Mt. Wilson as well as his reputation of being one of the best of the field. Hubble went to the observatory and began to work with Humason in an effort to collect more spectrums (Ibid).
And boy, did they not mesh. Humason was what many considered to be “an everyman” who just wanted to do his work but have fun with others. Hubble, a graduate of Oxford and not a dropout like Humason, was a former member of the army during World War I. Even though he saw no combat action, he still took his service with pride and preferred to be called Major Hubble. This hints at his possible feelings of superiority and at minimum is a demonstration of his ability to polarize people. He even had a British accent despite being born in Missouri! Many of his colleagues also describe him as desiring to be the center of attention. Despite all of these differences, the spectroscopy was needed and both men began to work (56).
At the time, the largest radial velocity (or movement along the line of sight, aka towards or away) known was recorded in the elliptical galaxy known as NGC 584 by astronomer M. Slipher in Flagstaff, Arizona, with a value of about 1,000 miles per second. But Humason was able to do better when he looked at elliptical galaxy NGC 7619 in the Pegasus Constellation. After a 33 hour exposure on a 100 inch telescope he was able to find a radial velocity of about 2,400 miles per second, After comparing the distance of this object and its radial velocity to NGC 584, they saw a direct proportion between distance and velocity. They found evidence of an expanding universe! (Voller 56, Humason)
Even though they had a small data set, they still published their results in Proceedings of the National Academy of Science in 1929. Hubble knew that if the universe was expanding that possible evidence for the cosmological constant, a numerical construct in many field equations that predicts the expansion (or contraction) factor of the universe. Humason, however, was not enthused about taking another run at the telescope. The reasons were not personal but more about working conditions. The prisms of the time used in spectroscopy were yellow in nature and not good at collecting light from portions of the spectrum. To ensure a good exposure for objects that were hundreds of times fainter than most imaged at that time, long exposures requiring days would be needed. For Humason, it meant a long time in cold, cramped conditions as he worked the equipment (Voller 56-7).
Hubble, perhaps more out of a desire to get great data rather than care for Humason, appeals to Hale to somehow make the working conditions better for Humason. Hale always had liked Humason and thus made the arrangements as fast as possible for improvements to the tech that was being utilized. John Anderson was able to create a new camera that had a decreased necessary exposure time by a significant factor. In fact, the time needed to image a galaxy like NGC 7619 was brought down to 4-6 hours instead of the 33 normally needed. Humason was definitely onboard with these improvements and rejoins Hubble. Over a 2 year period they record even more data and were able to confirm the Hubble Law as fact (57).
Humason, Milton L. “The Large Radial Velocity of NGC 7619. From the Proceedings of the National Academy of Sciences Vol. 15, No. 3, 15 Mar. 1929. Print.
Voller, Ron L. “The Man Who Measured the Cosmos.” Astronomy Jan. 2012: 52, 54-7. Print.
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© 2016 Leonard Kelley