Henrietta Swan Leavitt

“P.E. Robinson, "Introductory Astronomy: Galaxy Distances and Lookback Time" video includes Leavitt's contribution”

“H.S. Leavitt, "Periods of 25 Variable Stars in the Small Magellanic Cloud" Harvard College Observation Circular, Issues 151-200 @GoogleBooks”

“H.S. Leavitt, "The North Polar Sequence" (1917) No.3 in Annals of the Astronomical Observatory of Harvard College Vol.71 Miscellaneous Observations Relating to Photographic Magnitudes”

“By the death of Miss Leavitt on December 12, 1921, the Observatory lost an investigator of the highest value. She had obtained a comprehensive experience in photographic photometry, and had developed a clear appreciation of the difficulties involved in the theory and practice of this important research. Her work on standard magnitude sequences was nearly concluded at the time of her death, but she had hardly begun work on her extensive program of photographic measures of variable stars. In the foregoing summary no mention has been made of Miss Leavitt's work on standard photometry...”

“The following statement regarding the periods of 25 variable stars in the Small Magellanic Cloud has been prepared by Miss Leavitt.”

“I should be willing to pay thirty cents an hour in view of the quality of your work, although our usual price, in such cases, is twenty five cents an hour.”

“She deserved the Nobel Prize for her work.”

“She and others realized that one needed only to calculate the distance to these [Magellanic] Cepheids, which almost certainly were roughly the same distance to the earth, to have a useful yardstick for measuring other distances.”

“As a senior in 1892 Leavitt was introduced to astronomy. She was fascinated by it, and after graduation she enrolled in a course to study the subject full time. Tragically Henrietta Leavitt was suddenly struck down by a serous illness, and she was forced to spend over two years at home recovering. Her illness left her profoundly deaf. ...when she felt fit enough she put forward her name in 1895 as a volunteer worker at Harvard College Observatory.”

“Hubble tackled two of the most fundamental questions of the universe: how old is it, and how big? To answer both it is necessary to know two things—how far away certain galaxies are and how fast they are flying away from us. The red shift gives the speed at which galaxies are retiring, but doesn't tell us how far away they are to begin with. For that you need what are known as "standard candles"—stars whose brightness can be reliably calculated and used as benchmarks... Hubble's luck was to come along soon after an ingenious woman named Henrietta Swan Leavitt had figured out a way to do so.”

“Apart from her few and very important scientific papers, Leavitt left behind almost no traces of her life. She was born on the Fourth of July 1868 in Lancaster, Mass., and died of cancer on Dec. 12, 1921. Her will tells nearly all. She left an estate worth $314.91, mostly in Liberty Bonds, with a few items such as a desk valued at $5. She never married and had few living relatives. She also left behind a legacy of a great astronomical discovery.”

“Miss Leavitt was of an especially quiet and retiring nature, and absorbed in her work to an unusual degree. She had the highest esteem of all her associates at the Harvard Observatory, where her loss is keenly felt.”

“In addition to these larger labors, Miss Leavitt took part in various minor investigations. She gave considerable time to the discovery of new celestial objects. Altogether, she found 4 new stars, 2400 variable stars, or about one half of the known variables, and various asteroids and other objects.”

“One of the most striking accomplishments of Miss Leavitt was the discovery of 1,777 variable stars in the Magellanic Clouds. These results were [made] possible by photographs of long exposure made at Arequipa with the 24-inch Bruce refractor and forwarded to Cambridge. Some of these plates had exposures of from two to four hours and showed very faint stars, among which nearly all the variables are found. ...from a study of 25 of them, the important law was derived, that the length of period bears a definite relation to the absolute magnitude.”

“About 1906 a Durchmustering of variable stars was proposed at the Harvard Observatory. Somewhat later this was undertaken on plates included in the Map of the Sky... A comparison of the photographs of a number of these regions by Miss Leavitt led to the discovery of several hundred variables and other special objects. Among them were a number of stars of the Algol type.”

“It is hoped that systematic study of the light changes of all the variables, nearly two thousand in number, in the two Magellanic Clouds may soon be undertaken at this Observatory.”

“It is to be hoped, also, that the parallaxes of some variables of this type may be measured.”

“Since the [Cepheid] 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.”

“Apparently no sharp dividing line can be drawn between true Algol stars and those whose variations are continuous. Periods of nine variables in this region, which are of the Algol type or closely resemble it, have been determined and are here discussed.”

“It is worthy of notice that in Table VI the brighter variables have the longer periods. It is also noticeable that those having the longest periods appear to be as regular in their variations as those which pass through their changes in a day or two.”