Henrietta Swan Leavitt citations

Henrietta Swan Leavitt est une astronome américaine ayant découvert la relation entre la luminosité des étoiles variables et leur période de variation. En 1893, diplômée du Radcliffe College, Leavitt commença à travailler à l'observatoire de l'université Harvard, en tant que calculatrice, s'occupant d'examiner des plaques photographiques dans le but de mesurer et de cataloguer la luminosité des étoiles.

Bien que ses mérites n'aient été que très peu reconnus de son vivant, ce fut sa découverte d'une relation entre la luminosité de certaines étoiles variables, les céphéides, et le rythme de leurs pulsations qui permit aux astronomes de mesurer la distance entre la Terre et les autres galaxies. Elle expliqua sa découverte : « Une ligne droite peut facilement être dessinée entre les deux séries de points correspondant au maximum et au minimum, montrant qu'il y a une relation simple entre la luminosité des variables et leurs périodes ». Cette relation a été quantifiée plus tard par Ejnar Hertzsprung. Après la mort de Leavitt, Edwin Hubble repéra des céphéides dans la nébuleuse d'Andromède et put ainsi en déterminer la distance, bien plus grande que ce que l'on pensait, faisant de cette nébuleuse une galaxie. Plus tard, le même Hubble étudia des décalages spectraux, mesurés pour la première fois par l'astronome Vesto Slipher, dans la lumière de galaxies plus lointaines et prouva ainsi l'expansion de l'univers . Wikipedia  

✵ 4. juillet 1868 – 12. décembre 1921
Henrietta Swan Leavitt photo
Henrietta Swan Leavitt: 8   citations 0   J'aime

Henrietta Swan Leavitt: Citations en anglais

“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.”

Periods of 25 Variable Stars in the Small Magellanic Cloud http://adsabs.harvard.edu/abs/1912HarCi.173....1L (1912)
Contexte: A remarkable relation between the brightness of these [Cepheid] variables and the length of their periods will be noticed. In H. A. 60, No.4, attention was called to the fact that the brighter variables have the longer periods, but at that time it was felt that the number was too small the drawing of general conclusions. The periods of 8 additional variables which have been determined since that time, however, conform to the same law. The relation is shown graphically in Figure 1... The two resulting curves, one for the maxima and one for the minima, are surprisingly smooth, and of remarkable form. In Figure 2, the abscissas are equal to the logarithms of the periods, and the ordinates to the corresponding magnitudes, as in Figure 1. 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. The logarithm of the period increases by about 0.48 for each increase of one magnitude in brightness.

“The discovery of variable stars”

"Ten Variable Stars of the Algol Type" http://books.google.com/books?id=UkdWAAAAYAAJ&pg=PA87 (1908) Annals of the Astronomical Observatory of Harvard College Vol.60. No.5
Contexte: The discovery of variable stars, at this Observatory and elsewhere, has progressed so rapidly during the last five years, that the difficulty of keeping pace in observing and discussing them has become very great. In the study of distribution now in progress here, 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. When new lists of variables are published, therefore, it should be remembered that their discovery does not interfere materially with the study of individual objects. The number of these is so large that the publication of full results for all must be greatly delayed.

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

Periods of 25 Variable Stars in the Small Magellanic Cloud http://adsabs.harvard.edu/abs/1912HarCi.173....1L (1912)

“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.”

"1777 Variables in the Magellanic Clouds" http://books.google.com/books?id=UkdWAAAAYAAJ&pg=PA87 (1908) Annals of the Astronomical Observatory of Harvard College Vol.60. No.4

“The range of H 1255 is only four tenths of a magnitude, and on account of its brightness it is difficult to observe on all plates except those taken with the 1-inch Cooke lens. It seemed necessary, therefore, to take unusual precautions in order to secure accurate observations, and to give each one its full weight. Accordingly, one hundred and thirty six photographs were selected, including nearly all of those taken with the Cooke lens, and also those taken with the 8 inch Bache Telescope on which the variable was certainly faint. Four independent estimates of brightness were made on each plate, and means were taken, thus reducing the probable error one half. The phase was computed for each observation, thus covering all parts of the light curve. …H 1255 and H 1303 differ from the other variables in a marked degree as in each case the duration of the phase of minimum is very long in proportion to the length of the period. This fact led to considerable difficulty in determining their periods as they were apparently at their minimum brightness for some time before and after the actual minima occurred. In H 1255, the change in brightness is obviously continuous throughout the period, although it is much more rapid near minimum than near maximum. This is clearly seen in Plate IV, Figs. 5 and 6.”

"Ten Variable Stars of the Algol Type" http://books.google.com/books?id=UkdWAAAAYAAJ&pg=PA87 (1908) Annals of the Astronomical Observatory of Harvard College Vol.60. No.5

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