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Harlow Shapley: An American Astronomer Who Measured the Galaxy
'Some piously record "In the beginning God", but I say "In the beginning hydrogen".'
This is perhaps one of the most controversial statements from the American astronomer Harlow Shapley, who was also known as a humanitarian and internationalist. Shapley secured his place in the pages of the history books by estimating the size and dimensions of the Milky Way galaxy correctly. He used the position of the sun within the Milky Way and the RR Lyrae variable stars to come up with an accurate measurement. This significant discovery also discredited the pervading beliefs about the Earth and the Sun’s location in the galaxy.
Harlow Shapley was the first person to determine Earth’s actual place in the galaxy. This remarkable discovery, which was the result of painstaking calculations and detailed observations, has often been likened in importance to the discovery that the planet Earth in fact orbits the Sun, instead of the other way around.
Shapley received many awards and recognitions during his lifetime and he continued to contribute until he reached advanced age. He remained active in the scientific circuit even in his seventies, and only stopped giving lecture tours when his strength started to fail him in his eighties. Harlow Shapley died on October 20, 1972 in Boulder, Colorado in a nursing home.
Where is Nashville, Missouri?
Growing up in Missouri
Harlow Shapley was born on November 2, 1885 in Nashville, Missouri. His father, Willis Shapley was a farmer who provided for his family. His mother was Sarah Stowell Shapley who was a schoolteacher. He was born to a simple life in a farmhouse. Harlow had a twin brother named Horace and a younger brother named John.
Harlow dropped out of school after reaching the equivalent of a fifth grade education at a rural school nearby. Afterward, he studied at home, read extensively at the local library, and worked at the local newspaper, the Daily Sun. He worked as a police reporter in Joplin, Missouri before enrolling in a high school program to continue his education. The academic program was designed to be completed in six years, but Harlow graduated class valedictorian after fulfilling all the coursework and requirements in a mere two years.
On April 15, 1914, Harlow Shapley was married to Martha Betz. The couple met in Missouri in a mathematics class. Aside from being husband and wife, the two collaborated on several scientific papers, complementing each other’s scientific pursuits. Martha assisted her husband in the work that he did at the Mount Wilson Observatory and the Harvard College Observatory. Martha Betz Shapley devoted her own studies to eclipsing binaries and became a respected authority on the subject. She also studied other astronomical objects in her long career. Martha Shapley passed away in 1981.
Harlow and Martha produced five children—four sons and one daughter. One of Harlow Shapley’s sons, Lloyd Shapley became a world-renowned mathematician and economist. Lloyd Shapley, now in his nineties, was awarded the Sveriges Riksbank Nobel Memorial Prize in Economic Sciences (Nobel Prize in Economics) in 2012.
When Harlow was 22 years old, he entered the University of Missouri as a journalism undergraduate. However, the School of Journalism would not be opening until the next school year. While referring to the course directory, he decided to study Astronomy, one of the first subjects that he came across. He has been fascinated with science every since he was young. Archaeology was written before it on the list of topics, but Shapley did not consider the subject because he could not pronounce the word properly. Shapley ended up abandoning a potential career in journalism for one in science. It was a fortuitous choice, one that benefited the scientific community and humanity in general.
During his fellowship at Princeton University, Harlow Shapley was a post-graduate student under Henry Norris Russell. From 1914 to 1919, Shapley and other astronomers used the Mount Wilson Observatory 60-inch reflecting telescope. This facility in California housed the largest telescope in the world at that time. He produced significant work as a post-graduate student, particularly in providing scientific evidence that Cepheid variable stars behaved more like pulsators than spectroscopic binaries.
During his stay at Princeton, he chose eclipsing binary stars as the topic of his doctoral dissertation. Harlow Shapley published around 40 scientific papers as a post-graduate student in his quest to understand better the nature of the Universe and the objects that inhabit it.
Globular Cluster of Stars
Shapley and the Copernican Principle
Harlow Shapley was the first astronomer to pay close attention to the position of the sun within the Milky Way galaxy. At the Mount Wilson Observatory, Harlow Shapley used the telescope to identify Cepheid variable stars located in the nearest globular clusters that he could see. Globular clusters are remote, concentrated stellar systems. They are composed of tens of thousands of individual stars and appear to the observer as spherical forms. These clusters are located outside the plane of the Milky Way.
His observations of stars and globular clusters led him to the belief that the Milky Way, our home galaxy, was much larger than previously thought and he sought to provide definitive evidence. As a result of his calculations, he determined that the sun was in a rather nondescript location, and follows theCopernican principle that the Earth was not in the center of the Universe. He also believed that spiral nebulae observed through the telescope were located within the Milky Way, although this was proven wrong.
Henrietta Swan Leavitt and Cepheid Variable Stars
Measuring our place in the Galaxy
How did Harlow Shapley arrive at the galactic dimensions that changed the way that humans view their place in the Universe forever?
Using the luminosity-period relationship proposed earlier by Henrietta Swan Leavitt, Shapley determined the relative distances of the stars in question—the Cepheid variable stars that he observed. The distances to nearby globular clusters were calculated using this method. For the clusters that did not have visible Cepheid stars other methods were used, one of which is the inverse square law in determining relative distances between galaxies. During that time, the measurements were based on current scientific principles, most of which were assumptions that did not yet have physical evidence. However, as a testament to Shapley’s skills as a scientist and mathematician, the figures that he produced from his observations were quite close to modern measurements using calculations that are more sophisticated.
Harlow Shapley arrived at the figures by devising a new method based on the works of Leavitt and Bailey, exploiting the known period-luminosity relationship and at the same time calibrating the luminosity or absolute brightness. He was unable to apply direct trigonometric method in the calculations so he resorted to statistical procedures in determining the distance and luminosity of a Cepheid variable. This was a new approach that had never been applied in any prior attempt to measure galactic dimensions.
The measurement method that Harlow Shapley devised for stellar distances was borne out of patience and hard work. It took eleven papers on star clusters before he could reach a definitive conclusion, but his proposed galactic structure, though radical, was founded on undeniable evidence. Shapley plotted the clusters based on their location as revealed by the measurements. As a result, a more realistic layout of the Milky Way galaxy emerged. The revelations about galactic dimensions were a shock to some of the members of the scientific community, but it was undeniable. It was a very exciting time in astronomy. Harlow Shapley’s hard work paid off. The respect and accolades that followed were very much deserved indeed.
The Andromeda Galaxy
Our place in the Milky Way Galaxy
Harlow Shapley’s research showed that the Sun was not even at the center of the galaxy, but at the edge, two thirds of the way from the center of the Milk Way in the galactic disk, about 30,000 light years away. Before this discovery, the dominant belief in the scientific community was that that the Solar System was located at the very center of the Milky Way. Shapley’s work debunked this theory for good. It was a huge advance in galactic astronomy at that time.
Shapley believed that the Milky Way galaxy was much larger than the figures produced by any of his contemporaries. He estimated that the galaxy was about 300,000 light years in diameter. By using the apparent size of the globular clusters to determine their distance, he was able to determine that these clusters formed a loose halo around the body of the galaxy. From there, he came up with the galactic dimensions that also put the Sun at a less “special” location.
We know now that our galaxy is a barred spiral galaxy and just one of billions of galaxies in the Universe. We also know now that all the stars that we see in the night sky are part of the Milky Way. The exact measurements of the size of the Milky Way has since been determined, as well as the Sun’s exact location. The results of Shapley’s calculations were not far from the mark. The Milky Way galaxy has a diameter of 100,000 light years. This means that it will take light 100,000 years to travel from one end of the galaxy to the opposite end. The stellar disk is 1,000 light years thick. The gaseous disk is about 10,000 light years thick. At the nucleus, the measurement increases to about 30,000 light years.
We also know now that the Solar System is approximately 25,000 light years from the center of the galaxy, which lies in the direction of the constellation Sagittarius. Our Sun is located in the Orion Spur of the galaxy, a minor arm that is located between two major spiral arms, namely the Perseus Arm and the Sagittarius Arm. The Milky Way divides the sky into two hemispheres that are roughly equal, supporting the observation that the Sun and the planets lie close to the galactic plane.
A passion for science
Aside from the globular clusters, which he studied extensively, Shapley also developed an interest in the Magellanic Clouds, the galaxies that are in the proximity of the Milky Way. He referred to them as “metagalaxies,” referring to their natural tendency to occur in clusters. Creating catalogs on galaxies also occupied Shapley’s time.
Shapley was a passionate believer that spiral nebulae (galaxies) were within the Milky Way, and participated in the Great Debate against Heber D. Curtis in April 1920. Curtis won the argument. This particular debate incited the birth of extragalactic astronomy. Although Shapley’s side of the argument was proven wrong later by Edwin Hubble, he contributed significantly to the advancement of the growth of science an astronomy by encouraging curiosity, dialogue, and a tireless search for truth amongst his fellow astronomers.
Harlow Shapley was also known for the “Liquid Water Belt” Theory or the Habitable Zone concept. He published “Liquid Water Belt” in 1953 in support of Hubertus Strughold’s ecosphere theory. He was passionate about the quest for truth, and though the sides he chose were not always the popular view, he was respected in the scientific community for his candor and dedication to his work.
During his career, he published many books on astronomy and other scientific topics. The books that bore his byline included “Star Clusters,” and “Flights from Chaos,” which were both published in 1930. In 1943, he wrote a book entitled, “Galaxies.” In 1957, he published, “The Inner Metagalaxy,” and in 1953, he wrote “Of Stars and Men.”
Harlow Shapley was also famous for his affinity for ants. He delved deeply in to myrmecology, or the scientific study of ants, which he approached with the same passion and dedication that he devoted to astronomy.
Key positions held and awards received
Harlow Shapley was appointed to serve as the Director of Harvard College Observatory (HCO) in 1921 to replace the seat vacated by the deceased former director Edward Charles Pickering. Shapley developed the astronomy program of this prestigious university into of the best in the world until he vacated the position in 1952. In the same year, he was named the Paine Professor of Astronomy at Harvard and Director Emeritus. Because of his efforts, the Harvard Observatory attracted the very best young astronomers from around the world. One of the people who came to Harvard was a European scientist who, along with other Jewish refugees benefited from Shapley’s humanitarian efforts in the 1930s.
In 1926, Shapley was awarded the Henry Draper Medal by the National Academy of Sciences. Meanwhile, in 1933, Shapley received the Rumford Prize from the American Academy of Arts & Sciences and from the French Astronomical Society the Prix Jules Janssen. One year after in 1934, he was awarded a Gold Medal by the Royal Astronomical Society.
In 1935, he served as a member of the Board of Trustees of the Society for Science and the Public, a position that he held until 1971. The Astronomical Society of the Pacific granted him the honor of receiving the Bruce Medal in 1939. Shapley served as a member of the original standing committee of the Foundation for the Study of Cycles from 1941 onwards. In 1945, the Franklin Institute bestowed upon him the Benjamin Franklin Medal.
Shapley was a recipient of the Pius XI Medal in 1941. In the 1940s, Shapley was active in the political discussions of the day, one he became one of the key figures that came together to form the United Nations Educational, Scientific and Cultural Organization (UNESCO). Shapley was the individual responsible for the addition of the “S” for “Scientific” in the name of this agency of the United Nations. From 1943 to 1946, he was the President of the American Astronomical Society. In 1947, after World War II, he was elected President of the American Association for the Advancement of Science. Harlow Shapley was the elected representative of Harvard University in the 220th Anniversary of the Russian Academy of Sciences in Moscow in the year 1945. Shapley received the Henry Norris Russell Lectureship from the American Astronomical Society in the year 1950.
The legacy of Harlow Shapley
Harlow Shapley’s legacy continues to this day, and not only in the scientific discoveries that he had made, which greatly improved our understanding of the Universe and our place in it. His involvement in international affairs during his time can still be felt today, with the institutions that he helped build, such as the UNESCO. It was his enthusiasm for science in general that influenced the movers and shakers of society to fund scientific endeavors, and this has since become a tradition that has led to hundreds of important discoveries in the past half a century.
Shapley was one of the most prolific scientists of his generation. Although he was a controversial figure, in part because of his agnosticism and due to his beliefs with regard to certain scientific doctrines, his passion for astronomy helped increase public awareness of the sciences.
In recognition of his achievements in astronomy, the Shapley Supercluster was named after Harlow Shapley, as well as the Asteroid 1123 Shapleya and Shapley Crater on the Moon.
Shapley, Harlow. Through rugged ways to the stars. Scribner. 1969.
West, Doug. Harlow Shapley - Biography of an Astronomer: The Man Who Measured the Universe. C&D Publications. 2015.