Titlebook: Unveiling the Universe; An Introduction to A J. E. Zyl Textbook 1996 Springer-Verlag London Limited 1996 astronomy.cosmology.galaxies.instr

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The Dawn of Astronomy,. After about 3 1/2 days, the Moon moves to position 2 and has the appearance of a thin crescent, b. After 7 days, it is at right angles to the direction of the Sun, at position 3, and has the appearance of a half moon, c.

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Fundamental Measurements,four moons disappeared behind Jupiter became systematically later as the Earth moved away from its position of opposition, E. (Figure 5.2), to the other side of the Sun, E.. As the Earth came back towards opposition, the times became earlier.

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The Formulation of Laws,The next step in deciphering the secrets of the Universe was made by Nicolaus Copernicus (1473–1543). Although a priest in the Roman Catholic Church, he spent many years studying the movements of the Sun, Moon and planets against the background of stars.

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Instruments,Good progress was made in the development of the telescope during the first half of the 17th century. The first telescopes were refractors, having an objective lens and ocular, or eyepiece, on the optical axis. The principle of the refractor is illustrated in Figure 4.1.

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Surveying the Planets,Astronomy made rapid progress during the 17th, 18th and 19th centuries, thanks to the telescope. With the telescope it was possible to sight with precision and to determine the positions of stars and planets very accurately. The filar micrometer, in the eyepiece, made it possible to measure angular separations of very small angles.

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Variable Stars,Besides the method of naming stars, described on page 165, it was decided that capital letters before the genitive of the Latin name of the constellation be used only from A to Q. Letters from R to Z were to be reserved for variable stars, such as R Coronae Borealis, U Geminorum, etc.