By Jenna Fattah, Bicentennial Intern, Class of 2019, History and Media Management, Bloomington
Origins
IU students will recognize the name Kirkwood from Kirkwood Hall, Kirkwood Avenue, and Kirkwood Observatory, but not many know the story of astronomer and IU professor Dr. Daniel Kirkwood.[1]
Daniel Kirkwood was born on September 27, 1814 in Hartford County, Maryland into an agrarian family.[2] He began his career as a teacher in Hopewell, Pennsylvania at the age of 19 when one of his students introduced him to algebra, inspiring him to enroll in York County Academy in 1834.[3] After graduation in 1838, he was appointed mathematical instructor at York County Academy.[4] Below is a sketch of York County Academy around the same time that Daniel Kirkwood attended and taught.
In an 1845 publication of the Journal of the Linnaean Association of Pennsylvania College, Kirkwood voiced his skepticism of the astronomical theory Bode’s Law that theorized asteroids had a catastrophic origin, which would shape his own theories on asteroids.[5] This initial skepticism would later influence his theory on asteroid gaps over the next two decades.
In 1849, prominent American astronomer Sears Cook Walker took an interest in Daniel Kirkwood’s findings on the rotations and revolutions of planets, and he presented Kirkwood’s findings on his behalf to the Smithsonian Institution. Kirkwood’s conceptual work on asteroids earned him accolades as discovering “the most important harmony in the Solar System discovered since the time of Kepler,” which helped establish his reputation as “the American Kepler” and “the Kepler of our time,” perhaps with a touch of hyperbole.[6]
Nevertheless, Kirkwood’s Gaps and Kirkwood’s Law became the foundation for future scientists’ discoveries.
This compliment is astounding as 17th century astronomer Johannes Kepler revolutionized Astronomy with his laws of planetary motion, which provided foundation for future scientists like Isaac Newton.
After presenting at the annual meeting of the American Association for the Advancement of Science in Cambridge, Massachusetts in 1849, Kirkwood published his formula for the rotation periods of the planets in the proceedings of the American Association for the Advancement of Science.[7] His theory, which became known as Kirkwood’s Law, stated the square of the number of rotations made by a planet during one revolution around the sun is proportional to the cube of the diameter of its sphere of attraction.[8]
Kirkwood’s Time at Indiana University
Kirkwood taught at Delaware College in Newark from 1851-1856.[9] In 1856, he joined the IU faculty. During his 30-year tenure, he published 98 papers and two books.[10] Kirkwood continued his work on asteroids; he turned his focus to the orbital periods of asteroids orbiting Jupiter. He then decided he must study each asteroid to prove his hypothesis; at that time only 50 asteroids had been identified.[11][12]
In 1866, as the number of asteroids discovered increased over the decades and furthered his research, Kirkwood formulated his findings on asteroid gaps. Kirkwood pointed out the consistent gaps at the orbital periods between asteroids and Jupiter, illustrating they were not as chaotic or random as previously believed. These gaps were actually a result of “periodic perturbations” by Jupiter.[13]
Later that year, influenced by his skepticism in 1845 about asteroid theory and these findings, Kirkwood identified what is now known as “Kirkwood Gaps” in the orbits or minor planets and asteroids. This theory stated “that in those spaces were simple commensurability of motion with that of Jupiter occurs, there must, be gaps in the asteroid zone.”[14] This theory of Jupiter’s influence on the orbital periods of asteroids still holds true today.
Kirkwood left IU for a year to teach at Washington and Jefferson College from 1866-1867.[15] He returned to IU and in 1869 wrote about the experience with fellow mathematics Professors Elisha Ballantine and Theophilus Wylie as they “witnessed the total eclipse of the sun, a most magnificent sight…endeavor(ed) to photograph the sun.”[16] Theophilus Wylie arranged many astronomical viewings on the roof of his house, including a November meteor shower that played an important role in Kirkwood’s later research when he spoke to the American Philosophical Society in July of 1885.[17]
One of Kirkwood’s important articles was “On the Nebular Hypothesis, and the Approximate Commensurability of the Planetary Periods” in the Monthly Notices of the Royal Astronomical Society. Here Kirkwood discussed the eccentricity of orbits and distances between asteroids and planets like Mars and Jupiter. He expands this research to discuss comets and meteors, the periods meteoric rings, and the mass of asteroids between Mars and Jupiter in 1869 and 1870.[18]
In 1871, Kirkwood wrote letters to Professor Wylie discussing rotations and the mass of planets compared to their satellites and the distance from the asteroid rings. He concludes: “In short, the hypothesis harmonies in a very remarkable manner with the known elements of the solar system.”[19]
By 1875, 146 asteroids were known to astronomers. Kirkwood presented his findings to the American Association for the Advancement of Science on almost double the asteroid gaps and Jupiter measurements, earning notable British Astronomer Richard A. Proctor to refer to Kirkwood as the “Kepler of our day.” Proctor also noted that he came to America specifically to see Kirkwood.[20]
Kirkwood published a report on “The Asteroids between Mars and Jupiter” in the Smithsonian Institution’s 1877 Annual Report. The report emphasized that the discoveries and observations came at a time of rapid research and discovery, so theories developed and underwent revision upon newer discoveries.
The introduction outlines Kirkwood’s report: “It is proposed (1) to arrange the planets between Mars and Jupiter in the order of their discovery; (2) to tabulate their elements in the form most convenient for purposes of comparison; and then, (3) by a discussion of these elements in their mutual relations, as well as in their relations to Jupiter, the planet by which their motions are chiefly disturbed, to exhibit the evidence they afford in regard to the formation and development of the planetary system.”[21]
In 1885 Kirkwood was honored when the street between the Courthouse and University previously known as 5th Street in Bloomington, IN, was renamed in his honor because of his impact during his time at IU and his work in astronomy.[22]
Retirement
Upon his retirement in 1886, Kirkwood was named Professor Emeritus. The IU Board of Trustees resolved:
We hereby tender to Dr. Daniel Kirkwood the sincere gratitude of the Board of Trustees for his nearly thirty years of patient, successful and renowned labors in Indiana University. All the relations between him and the Board of Trustees have always been of pleasantest character and no words are too strong to express the high esteem in which he is held by this Board and by all its individual members. In his intercourse with the Faculty of the University his upright conduct and scholarly bearing have at all times won the entire confidence and respect and by the students he has ever been held in affectionate reservation.[23]
Kirkwood was known for using a bell to call students to his classroom. Upon retirement, Kirkwood gave the bell to Joseph A. Miller, a former student of Kirkwood who also became a professor of astronomy at IU.[24]
Kirkwood’s Later Years
In 1889, Kirkwood and his wife moved to Riverside, California.[25] In retirement, Kirkwood still kept in contact with his peers at IU. He wrote to IU president Joseph Swain to congratulate him on his appointment.[26] In January of 1895 he wrote to Swain informing him that he would not be able to attend the dedication of the Kirkwood Observatory, saying his health was “feeble.”[27] Kirkwood was inducted into the Astronomical Society in 1890.[28] The following year Kirkwood was appointed as a Non-Resident Professor and Lecturer of Astronomy at Stanford University by its first president, and former IU president, David Starr Jordan.[29]
After multiple building fires on the original campus (one in 1854 which destroyed the chapel and library and another major fire in 1883), combined with the need for more space, new buildings were constructed on the current Dunn’s Woods campus. One new building was dedicated as Daniel Kirkwood Hall.[30] This was the first building dedicated to a living man on IU’s campus.[31]
In June of 1895, Kirkwood passed away at his home in Riverside, California. His death was preceded by the death of Theophilus Wylie, his long-time friend and colleague who was often mentioned in Kirkwood’s letters and journals. [32] The funeral service was held in Bloomington, IN at the Walnut Street Church.[33]
The IU Board of Trustees recognized the great service of Drs. Kirkwood and Wylie as “Scholars, teachers, and gentlemen and recognize that Indiana owes a debt of gratitude for their long services in the cause of higher education in the State. It has been through the labors of such men as these that Indiana University has made itself felt in the higher life of our State.”[34]
Three days after Kirkwood’s death, the IU Board of Trustees approved the creation of an astronomy department.[35] After construction was completed in 1900, Kirkwood Observatory was posthumously dedicated in his honor in 1901. However, it should be noted that Daniel Kirkwood’s findings resulted from mathematical calculations and not his own telescope observations.
Student and Faculty Reactions
The students revered Kirkwood, as evident in his treatment in The Dagger, a student-run publication from the fraternity Beta Theta Pi that shared opinions about IU professors. One opinion was: “It is with great pleasure that I let my thoughts dwell upon this good man and scholar…the world knows his ability as a teacher, we can say nothing but to his praise. There is not a student in college who does not love that man. He is always ready to assist, to please; always urbane, affable and good.”[36]
A few years later, The Dagger offered again similar sentiments: “All reverence him, all love him, all honor him. He is courteous, affable, generous, and always meets all with a loving smile.”[37]
Lasting Impact on the Scientific Community
Kirkwood’s impact lasted long after his death. Textbooks dating from the early 1900s as well as current texts feature Kirkwood’s research. One such example found in an “Introduction to Astronomy, 1928” textbook, states “Kirkwood long ago pointed out that if instability in the equatorial zone once set in, it would persist” when discussing weaknesses of the Laplacian hypothesis.[38]
Another instance of Kirkwood’s research came up in the discussion of Saturn: “If a meteor were to revolve in the vacant space between the rings known as Cassini’s division, its period would be nearly commensurable with the periods of four of the satellites….Kirkwood called attention to this relation, which is entirely analogous to that found in the case of the planetoids.”[39]
Most importantly, the textbook highlights Kirkwood’s notes on planetoid periods, that they are “infrequent, or entirely lacking, at the distance at with their periods would be ½, ⅓, ⅔ of Jupiter’s period….the existence of these remarkable gaps. It is supposed that the perturbations by Jupiter during indefinite ages have cleared these regions of the bodies that may once have been circulating them.”[40]
Astronomy textbooks today still note Kirkwood’s work on the Kirkwood Gaps in relation to asteroid research. Below is a graph featured in a 2016 textbook that shows “the number of asteroids with various orbital periods, which corresponds to different average distances from the sun… Notice the gaps created by orbital resonances with Jupiter.”[41]
Over a century after his death, Kirkwood’s contribution to science still stands and he remains an important figure on the IU campus.
Notes
[1] Robert J. Aley, “Biography: Daniel Kirkwood,” The American Mathematical Monthly 1, no. 5 (May 1894): 140, https://www.jstor.org/stable/2969702.
[2] Ibid.
[3] “Daniel Kirkwood.” Planet Facts, Planetfacts.org. Accessed November 9, 2018, http://planetfacts.org/daniel-kirkwood/.
[4] “A Loss to the Astronomical World,” San Francisco Chronicle, June 14, 1895, accessed September 7, 2018.
[5] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 28.
[6] Ibid.
[7] Ibid.
[8] Aley, 142.
[9] “September 5, 1865,” Indiana University, Board of Trustees Minutes, accessed September 20, 2018.
[10] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 33.
[11] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 31.
[12] Cathy Pilachowski, in person interview, September 1, 2018.
[13] Frank Edmondson, ”Alumni Talk,“ June 7, 1968.
[14] Aley, 143.
[15] History of IU, Page 269, Box 1, C83.
[16] Wylie Diary, August 7, 1869.
[17] Publications, November Meteors, Box 1, C52.
[18] Publications, Box 1, C52.
[19] Box 1, C202.
[20] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 31.
[21] Daniel Kirkwood. “The Asteroids Between Mars and Jupiter.” In Annual Report of Board of Regents of the Smithsonian Institution, 358-371. Washington, D. C. 1877.
[22] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 32.
[23] Board of Trustees Minutes, June 6, 1886.
[24] Frank Edmondson, Alumni Talk, June 7, 1968.
[25] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 32.
[26] Series Correspondence, Swain 1893, Box 1, C52.
[27] Series Correspondence, Swain 1895, Box 1, C52.
[28] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 28.
[29] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 32.
[30] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 30.
[31] Aley, page 140.
[32] Indianapolis Journal, Wednesday June 12, 1895, page 2
[33] San Francisco Chronicle, Obituaries, published June 14, 1895.
[34] Board of Trustees Minutes, June 13, 1895.
[35] Frank Edmondson, “Dean of American Astronomers,” Mercury Magazine, 2000, page 33.
[36] The Dagger Page 2, June 1875, Box 1, C591.
[37] The Dagger, June 1878, Box 1, C591.
[38] Moulton, page 451, Introduction to Astronomy, 1928.
[39] Moulton, page 304, Introduction to Astronomy, 1928.
[40] Moulton, page 260, Introduction to Astronomy, 1928.
[41] Jeffrey Bennet, Megan Donahue, Nicholas Schneider, Mark Voit, “The Cosmic Perspective: The Solar System.” Eighth Edition, Pearson Publishing, 2016. Print.