Apparently no sharp dividing line can be drawn between true Algol star — Henrietta Swan Leavitt

"A determination of the visual magnitudes of the stars had a very large place in the work of the Observatory during the first half of Professor Pickerings directorate. As soon as the need of photographic magnitudes became urgent, the importance of a standard sequence, from which the photographic magnitudes could be derived for stars anywhere in the sky, became evident. A sequence of stars of varying magnitudes had been early selected near the North Pole, and the determination of the magnitudes of the stars involved was assigned to Miss Leavitt. This work was carried out with unusual originality, skill, and patience."

"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."

"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."

"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 doesnt 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... Hubbles luck was to come along soon after an ingenious woman named Henrietta Swan Leavitt had figured out a way to do so."

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