Henrietta Swan Leavitt
Encyclopedia
Henrietta Swan Leavitt was an American astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

. A graduate of Radcliffe College
Radcliffe College
Radcliffe College was a women's liberal arts college in Cambridge, Massachusetts, and was the coordinate college for Harvard University. It was also one of the Seven Sisters colleges. Radcliffe College conferred joint Harvard-Radcliffe diplomas beginning in 1963 and a formal merger agreement with...

, Leavitt went to work in 1893 at the Harvard College Observatory
Harvard College Observatory
The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...

 in a menial capacity as a "computer"
Human computer
The term "computer", in use from the mid 17th century, meant "one who computes": a person performing mathematical calculations, before electronic computers became commercially available....

, assigned to count images on photographic plate
Photographic plate
Photographic plates preceded photographic film as a means of photography. A light-sensitive emulsion of silver salts was applied to a glass plate. This form of photographic material largely faded from the consumer market in the early years of the 20th century, as more convenient and less fragile...

s. Study of the plates led Leavitt to propound a groundbreaking theory, worked out while she labored as a $10.50-a-week assistant, that made possible the pivotal discoveries of astronomer Edwin Hubble
Edwin Hubble
Edwin Powell Hubble was an American astronomer who profoundly changed the understanding of the universe by confirming the existence of galaxies other than the Milky Way - our own galaxy...

. Leavitt's formulation of the period
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

-luminosity relationship of Cepheid variable stars
Cepheid variable
A Cepheid is a member of a class of very luminous variable stars. The strong direct relationship between a Cepheid variable's luminosity and pulsation period, secures for Cepheids their status as important standard candles for establishing the Galactic and extragalactic distance scales.Cepheid...

 provided the foundation for a paradigm shift
Paradigm shift
A Paradigm shift is, according to Thomas Kuhn in his influential book The Structure of Scientific Revolutions , a change in the basic assumptions, or paradigms, within the ruling theory of science...

 in modern astronomy, an accomplishment for which she received almost no recognition during her lifetime.

Early years and education

Henrietta Swan Leavitt, the daughter of Congregational church
Congregational church
Congregational churches are Protestant Christian churches practicing Congregationalist church governance, in which each congregation independently and autonomously runs its own affairs....

 minister George Roswell Leavitt and his wife Henrietta Swan (Kendrick), was born in Lancaster, Massachusetts
Lancaster, Massachusetts
Lancaster is a town in Worcester County, Massachusetts, in the United States. Incorporated in 1653, Lancaster is the oldest town in Worcester County...

, a descendant of Deacon
Deacon
Deacon is a ministry in the Christian Church that is generally associated with service of some kind, but which varies among theological and denominational traditions...

 John Leavitt
John Leavitt
Deacon John Leavitt was a tailor, public officeholder, and founding deacon of Old Ship Church in Hingham, Plymouth County, Massachusetts, the only remaining 17th-century Puritan meeting house in America and the oldest church in continuous ecclesiastical use in the United States...

, an English Puritan
Puritan
The Puritans were a significant grouping of English Protestants in the 16th and 17th centuries. Puritanism in this sense was founded by some Marian exiles from the clergy shortly after the accession of Elizabeth I of England in 1558, as an activist movement within the Church of England...

 tailor, who settled in the Massachusetts Bay Colony
Massachusetts Bay Colony
The Massachusetts Bay Colony was an English settlement on the east coast of North America in the 17th century, in New England, situated around the present-day cities of Salem and Boston. The territory administered by the colony included much of present-day central New England, including portions...

 in the early seventeenth century. (The family name was spelled Levett in early Massachusetts records.) She attended Oberlin College
Oberlin College
Oberlin College is a private liberal arts college in Oberlin, Ohio, noteworthy for having been the first American institution of higher learning to regularly admit female and black students. Connected to the college is the Oberlin Conservatory of Music, the oldest continuously operating...

, and graduated from Radcliffe College
Radcliffe College
Radcliffe College was a women's liberal arts college in Cambridge, Massachusetts, and was the coordinate college for Harvard University. It was also one of the Seven Sisters colleges. Radcliffe College conferred joint Harvard-Radcliffe diplomas beginning in 1963 and a formal merger agreement with...

, then called the Society for the Collegiate Instruction for Women, with a bachelor's degree in 1892. It wasn't until her fourth year of college that Leavitt took a course in astronomy, in which she earned an A–.

Career

Leavitt began work in 1893 at Harvard College Observatory as one of the women human ‘computers’
Harvard Computers
Edward Charles Pickering decided to hire women as skilled workers to process astronomical data. Among these women were Williamina Fleming, Annie Jump Cannon, Henrietta Swan Leavitt and Antonia Maury. This staff came to be known as "Pickering's Harem" or, more respectfully, as the Harvard Computers...

 brought in by Edward Charles Pickering
Edward Charles Pickering
Edward Charles Pickering was an American astronomer and physicist, brother of William Henry Pickering.Along with Carl Vogel, Pickering discovered the first spectroscopic binary stars. He wrote Elements of Physical Manipulations .Pickering attended Boston Latin School, and received his B.S. from...

 to measure and catalog the brightness of stars in the observatory's photographic plate
Photographic plate
Photographic plates preceded photographic film as a means of photography. A light-sensitive emulsion of silver salts was applied to a glass plate. This form of photographic material largely faded from the consumer market in the early years of the 20th century, as more convenient and less fragile...

 collection. (In the early 1900s, women were not allowed to operate telescopes). She noted thousands of variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...

s in images of the Magellanic Clouds
Magellanic Clouds
The two Magellanic Clouds are irregular dwarf galaxies visible in the southern hemisphere, which are members of our Local Group and are orbiting our Milky Way galaxy...

. In 1908 she published her results in the Annals of the Astronomical Observatory of Harvard College, noting that a few of the variables showed a pattern: brighter ones appeared to have longer periods. After further study, she confirmed in 1912 that the variable stars of greater intrinsic luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...

actually Cepheid variables did indeed have longer periods, and the relationship was quite close and predictable.

Leavitt's discovery is known as the 'period-luminosity relationship' which is a curvilinear relationship that becomes a straight line relation between the luminosity and the log
Logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...

 of the period. "A straight line can be readily drawn among each of the two series of points corresponding to maxima and minima," Leavitt wrote of her study of 1,777 variable stars recorded on Harvard's photographic plates, "thus showing that there is a simple relation between the brightness of the variable and their periods".

Leavitt used the simplifying assumption that all of the Cepheids in the respective Magellenic Clouds were approximately the same distances from the earth, so the relationship became key in determining Cepheid Scale Distance and absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...

s beyond the realm of parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...

 measurement, once the absolute distance to one Cepheid could later be determined by astronomers. "Since the variables are probably at nearly the same distance from the Earth, their periods are apparently associated with their actual emission of light, as determined by their mass, density, and surface brightness." This relationship would provide an important yardstick for measuring distances
Cosmic distance ladder
The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A real direct distance measurement of an astronomical object is possible only for those objects that are "close enough" to Earth...

 in the Universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

, if it could be calibrated. One year after Leavitt reported her results, Ejnar Hertzsprung
Ejnar Hertzsprung
Ejnar Hertzsprung was a Danish chemist and astronomer.Hertzsprung was born in Copenhagen. In the period 1911–1913, together with Henry Norris Russell, he developed the Hertzsprung–Russell diagram....

 determined the distance of several Cepheids in the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

, and with this calibration the distance to any Cepheid could be determined.

At the time, it was not clear that there were millions of nebulae
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...

 that were actually galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

 outside of our Milky Way galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

. Their distances were too extreme to be measured using parallax and the Cepheid period-luminosity relationship provided the key to estimating these distances. Cepheids were soon detected in other galaxies such as the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...

 (notably by Edwin Hubble in 1923–24). Cepheids were an important part of the evidence that galaxies are far outside of the Milky Way and were key to settling the Great Debate
The Great Debate
In astronomy, the Great Debate, also called the Shapley–Curtis Debate, was an influential debate between the astronomers Harlow Shapley and Heber Curtis which concerned the nature of spiral nebulae and the size of the universe...

 as to the nature of spiral nebulae and whether the Universe was larger than the Milky Way. Our picture of the universe was changed forever, largely because of Leavitt's discovery.
The accomplishments of Edwin Hubble
Edwin Hubble
Edwin Powell Hubble was an American astronomer who profoundly changed the understanding of the universe by confirming the existence of galaxies other than the Milky Way - our own galaxy...

, renowned American astronomer, were made possible by Leavitt's groundbreaking research and Leavitt's Law. "If Henrietta Leavitt had provided the key to determine the size of the cosmos
Cosmos
In the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...

, then it was Edwin Powell Hubble who inserted it in the lock and provided the observations that allowed it to be turned," wrote David H. and Matthew D.H. Clark in their book Measuring the Cosmos. To his credit, Hubble himself often said that Leavitt deserved the Nobel for her work. Gösta Mittag-Leffler of the Swedish Academy of Sciences had begun paperwork on her nomination in 1924, only to learn that she had died of cancer three years earlier (the Nobel prize cannot be awarded posthumously).

Leavitt worked sporadically during her time at Harvard, often sidelined by health problems and family obligations. An illness contracted after her graduation from Radcliffe College rendered her increasingly deaf. By 1921, when Harlow Shapley
Harlow Shapley
Harlow Shapley was an American astronomer.-Career:He was born on a farm in Nashville, Missouri, and dropped out of school with only the equivalent of a fifth-grade education...

 took over as director of the observatory, Leavitt was made head of stellar photometry
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...

. By the end of that year she had succumbed to cancer, and was buried in the Leavitt family plot at Cambridge Cemetery in Cambridge, Massachusetts
Cambridge, Massachusetts
Cambridge is a city in Middlesex County, Massachusetts, United States, in the Greater Boston area. It was named in honor of the University of Cambridge in England, an important center of the Puritan theology embraced by the town's founders. Cambridge is home to two of the world's most prominent...

.

"Sitting at the top of a gentle hill," writes George Johnson in his biography of Leavitt, "the spot is marked by a tall hexagonal monument, on top of which (cradled on a draped marble pedestal) sits a globe. Her uncle Erasmus Darwin Leavitt
Erasmus Darwin Leavitt, Jr.
Erasmus Darwin Leavitt, Jr. , also known as E. D. Leavitt, was a noted American mechanical engineer best known for his steam engine designs....

 and his family are also buried there, along with other Leavitts. A plaque memorializing Henrietta and her two siblings who died so young, Mira and Roswell, is mounted directly below the continent of Australia. Off to one side, and more often visited, are the graves of Henry
Henry James
Henry James, OM was an American-born writer, regarded as one of the key figures of 19th-century literary realism. He was the son of Henry James, Sr., a clergyman, and the brother of philosopher and psychologist William James and diarist Alice James....

 and William James
William James
William James was a pioneering American psychologist and philosopher who was trained as a physician. He wrote influential books on the young science of psychology, educational psychology, psychology of religious experience and mysticism, and on the philosophy of pragmatism...

."

Leavitt was a member of Phi Beta Kappa
Phi Beta Kappa Society
The Phi Beta Kappa Society is an academic honor society. Its mission is to "celebrate and advocate excellence in the liberal arts and sciences"; and induct "the most outstanding students of arts and sciences at America’s leading colleges and universities." Founded at The College of William and...

, the American Association of University Women, the American Astronomical and Astrophysical Society, the American Association for the Advancement of Science, and an honorary member of the American Association of Variable Star Observers. Her early passing was seen as a tragedy by her colleagues for reasons that went beyond her scientific achievements.

In an obituary her colleague, Solon I. Bailey, noted, "She had the happy faculty of appreciating all that was worthy and lovable in others, and was possessed of a nature so full of sunshine that, to her, all of life became beautiful and full of meaning."

Awards and honors

  • The asteroid
    Asteroid
    Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

     5383 Leavitt
    5383 Leavitt
    5383 Leavitt is an asteroid named after Harvard University astronomer Henrietta Swan Leavitt....

     and the crater Leavitt
    Leavitt (crater)
    Leavitt is a crater on the far side of the Moon. It is a moderately eroded crater, but only a few minor craterlets lie along the edge and interior. Most of these features lie within the northern half of the crater, but the largest lies along the southern inner wall. The crater has a low central...

     on the Moon
    Moon
    The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

     are named in her honor.
  • Unaware of her death four years prior, the Swedish mathematician Gösta Mittag-Leffler considered nominating her for the 1926 Nobel Prize in Physics
    Nobel Prize in Physics
    The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...

    , and wrote to Shapley requesting more information on her work on Cepheid variables, offering to send her his monograph on Sofia Kovalevskaya
    Sofia Kovalevskaya
    Sofia Vasilyevna Kovalevskaya , was the first major Russian female mathematician, responsible for important original contributions to analysis, differential equations and mechanics, and the first woman appointed to a full professorship in Northern Europe.She was also one of the first females to...

    . Shapley replied, let Mittag-Leffler know that Leavitt had died, and suggested that the true credit belonged to his (Shapley's) interpretation of her findings. She was never nominated, because the Nobel Prize is not awarded posthumously.

External links

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