23 May 2023

This Month in Astronomical History: June 2023

Stephen Spears Cleveland Public School

HAD LogoEach month as part of this series from the AAS Historical Astronomy Division (HAD), an important discovery or memorable event in the history of astronomy will be highlighted. This month's author, AAS Educator Affiliate Stephen Spears, commemorates the distinguished career of Vera Rubin. Interested in writing a short (500-word) column? Instructions along with previous history columns are available on the HAD web page.

All the Matter We Cannot See: The Invisible World of Vera Rubin

Science progresses best when observations force us to alter our preconception.
—Vera Rubin

In December of this year (2023), the newly constructed Vera Rubin Observatory is expected to be operational. This 8.4-meter telescope features a three-mirror design which creates an ultra-wide field of view. This unique instrument is located in Northern Chile and will employ the largest digital camera ever created. The telescope will be able to survey the entire Southern sky every few nights with a resolution that is the equivalent of seeing a golf ball from the Moon.1

Vera Rubin (nee Cooper) was born on 23 July 1928 in Philadelphia, Pennsylvania. Her fascination with astronomy developed at an early age. With the help of her father, she built a small telescope, using two lenses and a cardboard tube.2 Her father also encouraged her to become more interested in science by taking her to the local astronomy club to learn from Harlow Shapley and other guest lecturers.2 Vera Cooper was awarded a scholarship to Vassar and graduated Phi Beta Kappa as the school’s only astronomy major in 1948. She did this in spite of the advice from her high school physics teacher to avoid a career in science and stick with the humanities.

In 1948, Vera Cooper married Robert Rubin, who at the time was a graduate student studying physical chemistry and mathematics at Cornell.

When applying to graduate school, Vera Rubin was told that Princeton did not accept women in their graduate astronomy program, a policy that was not changed until 1975. Rubin was accepted to Harvard, but she decided to join her husband at Cornell and enrolled in a two-year master’s program. Cornell at that time had a small astronomy department that concentrated on only the basics of astronomy. Its physics department was, however, world-class, with Hans Bethe, Phillip Morrison, and Richard Feynman, whose course in chromo-electro dynamics she found quite challenging.3

Rubin completed her master’s degree in 1951. In her master’s thesis, she examined 108 galaxies with known radial velocities to see if there was a systematic motion in the system of galaxies in addition to their universal expansion. Rubin speculated that galaxies might rotate around an unknown center, and not just be expanding as put forth in the Big Bang theory.4

Rubin presented her ideas to the American Astronomical Society at the 84th meeting on 27-29 December 1950 in Haverford, Pennsylvania, in a 10-minute talk. As there was no scientific theory to support her findings, the audience did not receive her presentation well. Only Martin Schwarzschild, an eminent astronomer from Princeton, offered her any support.5

In 1951, Rubin and her newly confirmed PhD husband, moved to Washington DC, so he could start working at the John Hopkins Applied Physics Laboratory. To stay current with the world of astrophysics, she faithfully read the Astrophysical Journal in her extremely limited spare time.

Rubin, encouraged by her husband, enrolled in Georgetown University to pursue a PhD. At Georgetown, all graduate courses were offered at night. With help from her husband and her parents, Rubin negotiated a complicated schedule and completed her degree in 1954. Her thesis advisor was the brilliant but eccentric physicist George Gamow. He was not interested in the details of what Rubin was doing nor the mathematics involved. So, she was pretty much on her own. In her doctoral dissertation, Rubin showed that galaxies are not evenly distributed in the universe and are in some cases clumped together. This went against the accepted theory at the time of an isotropic universe. Fifteen years later the validity of her research was confirmed.5,6

For 10 years, Rubin taught classes at Georgetown, took care of four young children, and did research when she could find the time. In 1962, Rubin and six graduate students published a paper in the Astronomical Journal that stated for a radius (R), where R > 8.5 kpc, the stellar velocity curve of the Milky Way is flat and does not decrease as is expected for Keplerian orbits. This was Dr. Rubin’s first flat rotation curve paper. Once again, the paper was not well received.7

In 1965, she got a job working for the Department of Terrestrial Magnetism (DTM), which was part of the Carnegie Institution of Washington, where she remained for the rest of her career. At DTM, Rubin met W. Kent Ford, a young physicist who had developed a way to enhance the efficiency of a spectrograph by amplifying the image. This improved the quality of a spectrum by a factor of ten and greatly reduced exposure times.8

The Rubin and Ford paper, “Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission Regions,” published in the Astrophysical Journal in 1970, dramatically altered our understanding of the universe. The laws of Newtonian gravity predict that just like the outer planets of the solar system which orbit the Sun at a velocity less than the inner planets, the stars on the edge of a spiral galaxy should orbit slower than those stars in the center. Vera Rubin and Kent Ford showed that this is not true: stars at the edge of a spiral galaxy travel as fast as those near the center.9

Rubin and Ford determined that from the center to 0.5 kpc the velocities rise rapidly to approximately 228 km/sec and then at 2 kpc they drop dramatically to about 55 km/sec. The explanation for this initial rise and fall is related to the distribution of stars in the center. Initially the mass rises because there are more stars near the center, from about 0.2 kpc. However, beyond 0.5 kpc the density is quite low and that is reflected in very low rotational velocities. At R > 3 kpc there is a steep rise in velocity to more than 300 km/sec, and at 15 < R ≤ 24 kpc, the rotational velocity begins to flatten out to approximately 225 km/sec. The shape of the rotation curve from R > 3 kpc is determined by the amount of material beyond the central nucleus.

Although Rubin was very cautious to speculate as to why the rotation curve was not falling, the Rubin and Ford research showed that as the distance from a galaxy increases, the mass rises steadily. It was obvious that something unexplained was contributing massive amounts of non-luminous matter.10

In 1980, along with Norbert Thonnard, Rubin and Ford published a paper titled “Rotational Properties of 21 Galaxies with a Large Range of Luminosities and Radii, From NGC 4605 (R = 4 kpc) to UGC 2885 (R = 122 kpc).”

This paper reinforced Rubin and Ford’s previous work as to the flat velocity curve within M31 out to 24 kpc. They examined 21 Sc galaxies whose properties had a wide range of radii, masses, and luminosities. Sc galaxies are galaxies that, according to Edwin Hubble, have an exceedingly small nucleus and multiple spiral arms that are open with significant interstellar material for star formation.11 All curves show a rapid rise to Vrot 125 km/sec at approximately 5 kpc and a slower rise thereafter. To quote Rubin and Ford: “The conclusion is inescapable that non-luminous matter exists beyond the optical galaxy.”12

Vera Rubin passed away on 25 December 2016, at the age of 88, in Princeton, New Jersey. Her personal life was as extraordinary as her scientific life. She and her husband Robert were married for 60 years until his death in 2008. Outside of her family life, Vera Rubin was a pure scientist. Perhaps her own words sum up how she reflected on her lifelong research: “Fame is fleeting, my numbers mean more to me than my name. If astronomers are still using my data years from now that’s my greatest accomplishment.”

Vera Rubin analyzing photographic plates

Fig. 1: Vera Rubin analyzing photographic plates. (Image courtesy of the Carnegie Institution for Science.)

Rotational velocities of thirty-seven OB associations measured in M31, as a function of distance from the center.

Fig. 2: Rotational velocities of thirty-seven OB associations measured in M31, as a function of distance from the center. The solid curve is the adapted rotational velocity curve. The scale of this graph is based on the accepted distance of Andromeda at the time, 690 kpc. Using that distance, one arc minute is equal to 200 kpc. (Rubin and Ford, 1970).

The mean velocity in the plane of 21 Sc galaxies as a function of linear velocity from the nucleus.

Fig. 3: The mean velocity in the plane of 21 Sc galaxies as a function of linear velocity from the nucleus. All have the same flattening of the rotational velocity as one moves away from the center. (Rubin, Ford, and Thonnard, 1980).


  1. Boyle, Rebecca. (2023). “The Threat of Satellite Constellations.” Scientific American. Vol.328, No.2, p.46-51.
  2. Mitton, Jacqueline, and Mitton, Simon. (2021). Vera Rubin: A Life. Cambridge, Massachusetts & London, England: Belknap Press of Harvard Press.
  3. Rubin, Vera (2011) “An Interesting Voyage." Annual Review of Astronomy and Astrophysics 2011 49: 1-28.
  4. Rubin, Vera. George Gamow Symposium; ASP Conference Series, Vol. 129, 1997, ed. Eamon Harper, W.C. Parke, and David Anderson, p.95.
  5. Rubin, Vera, (2011) “An Interesting Voyage.” Annual Review of Astronomy and Astrophysics 2011 49:1, 1-28.
  6. Rubin, Vera (1997). Bright Galaxies and Dark Matter. New York: American Institute of Physics.
  7. Rubin, Vera. (2000). ‘One Hundred Years of Rotating Galaxies.” Publications of the Astronomical Society of the Pacific, 112: 747-750, 2000 June.
  8. Hunter, Deidra.(2017) “Vera Cooper Rubin (1928-2016).” Publications of the Astronomical Society of the Pacific, 129:040201 (4pp), 2017 April.
  9. Rubin, Vera. (1983) “The Rotation of Spiral Galaxies.” Science, 220:4604, 1983 June.
  10. Rubin, Vera, Ford, W. Kent. (1970) “Rotation of the Andromeda Nebula from A Spectroscopic Survey of Emission Regions.” The Astrophysical Journal, 159:379-403.
  11. Hubble, Edwin. (1936). The Realm of the Nebula. Yale University Press, New Haven & London.
  12. Rubin, Vera, Thonnard, N., Ford, W.K., (1980). “The Rotational Properties of 21 SC Galaxies With a Large Range of Luminosities and Radii, From NGC 4605 (R=4kpc) to UGC 2885 {R=122kpc)”. Astrophysical Journal. 238: 471-487.

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