Henrietta Swan Leavitt

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.

A straight line can readily be drawn among each of the two series of points corresponding to the maxima and minima, thus showing that there is a simple relation between the brightness of the variables and their periods.

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 …

the actual time devoted to the search for new variables is small, but thorough observation requires much time, while the discussion of results may be prolonged almost indefinitely.

has progressed so rapidly during the last five years, that the difficulty of keeping pace in observing and discussing them has become very great.

The discovery of variable stars

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 …