„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.“

—  Henrietta Swan Leavitt, Periods of 25 Variable Stars in the Small Magellanic Cloud http://adsabs.harvard.edu/abs/1912HarCi.173....1L (1912)
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„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.“

—  Henrietta Swan Leavitt astronomer 1868 - 1921
"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

Henrietta Swan Leavitt photo
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James Bradley photo

„If we suppose the distance of the fixed stars from the sun to be so great that the diameter of the earth's orbit viewed from them would not subtend a sensible angle, or which amounts to the same, that their annual parallax is quite insensible; it will then follow that a line drawn from the earth in any part of its orbit to a fixed star, will always, as to sense, make the same angle with the plane of the ecliptic, and the place of the star, as seen from the earth, would be the same as seen from the sun placed in the focus of the ellipsis described by the earth in its annual revolution, which place may therefore be called its true or real place.
But if we further suppose that the velocity of the earth in its orbit bears any sensible proportion to the velocity with which light is propagated, it will thence follow that the fixed stars (though removed too far off to be subject to a parallax on account of distance) will nevertheless be liable to an aberration, or a kind of parallax, on account of the relative velocity between light and the earth in its annual motion.
For if we conceive, as before, the true place of any star to be that in which it would appear viewed from the sun, the visible place to a spectator moving along with the earth, will be always different from its true, the star perpetually appearing out of its true place more or less, according as the velocity of the earth in its orbit is greater or less; so that when the earth is in its perihelion, the star will appear farthest distant from its true place, and nearest to it when the earth is in its aphelion; and the apparent distance in the former case will be to that in the latter in the reciprocal proportion of the distances of the earth in its perihelion and its aphelion. When the earth is in any other part of its orbit, its velocity being always in the reciprocal proportion of the perpendicular let fall from the sun to the tangent of the ellipse at that point where the earth is, or in the direct proportion of the perpendicular let fall upon the same tangent from the other focus, it thence follows that the apparent distance of a star from its true place, will be always as the perpendicular let fall from the upper focus upon the tangent of the ellipse. And hence it will be found likewise, that (supposing a plane passing through the star parallel to the earth's orbit) the locus or visible place of the star on that plane will always be in the circumference of a circle, its true place being in that diameter of it which is parallel to the shorter axis of the earth's orbit, in a point that divides that diameter into two parts, bearing the same proportion to each other, as the greatest and least distances of the earth from the sun.“

—  James Bradley English astronomer; Astronomer Royal 1693 - 1762
Miscellaneous Works and Correspondence (1832), Demonstration of the Rules relating to the Apparent Motion of the Fixed Stars upon account of the Motion of Light.

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„That the emission of light must waste the sun, is not a difficulty that can be opposed to our hypothesis.“

—  William Herschel German-born British astronomer, technical expert, and composer 1738 - 1822
Context: That the emission of light must waste the sun, is not a difficulty that can be opposed to our hypothesis. Many of the operations of Nature are carried on in her great laboratory which we cannot comprehend. Perhaps the many telescopic comets may restore to the sun what is lost by the emission of light.<!-- p. 148 Ch.4 "Life and Works" quote from his paper "Nature and Construction of the Sun and Fixed Stars" (1795).

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„Atheism is so senseless. When I look at the solar system, I see the earth at the right distance from the sun to receive the proper amounts of heat and light. This did not happen by chance.“

—  Isaac Newton British physicist and mathematician and founder of modern classical physics 1643 - 1727
Disputed, As quoted in Isaac Newton: Inventor, Scientist, and Teacher (1975) by John Hudson Tiner. "Atheism is so senseless" is a statement Newton made indeed in "A short Schem of the true Religion", but no source for the rest of this statement has been located prior to 1975. Part of this statement might originate as a summation of observations by Colin Maclaurin in his An Account of Sir Isaac Newton's Philosophical Discoveries (1750), Book III, Ch. 5 http://books.google.com.au/books?id=yS1PAAAAcAAJ&pg=PA307#q=%22wisdom%20of%20the%20author%22: "On the quantity of watter and density of the sun and planets" : "… the earth … those planets which are nearer the sun are found to be more dense, by which they are enabled to bear the greater heat of the sun. This is the result of our most subtle enquiries into nature, that all things are in the best situations, and disposed by perfect wisdom. If our earth was carried down into the orb of Mercury, our ocean would boil and soon be dissipated into vapour, and dry land would become uninhabitable. If the earth was carried to the orb of Saturn, the ocean would freeze at so great a distance from the sun, and the cold would soon put a period to the life of plants and animals. A much less variation of the earth's distance from the sun than this would depopulate the torrid zone if the earth came nearer the sun, and the temperate zones, if it was carried from the sun. A less heat at Jupiter's distance … might be as fatal … proves on every occasion, the wisdom of the author."

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