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A comprehensive theory about the cosmos resulted from careful (visually) following the events in the sky, combined with philosophical reasoning. A spherical earth was positioned in the center of the universe. Anything beyond the Moon was perfectly spherical, moving around in (superpositions of) circular orbits. A backdrop of unchangeable stars was far away, pinned on a crystal sphere. Aristotle (384 BC) codified this as comprehensive theory. The oldest catalogue of brighter stars (“Almagest”) was compiled by Ptolemy about AD 150. Developments were driven by scientific curiosity, dating religious feasts, and astrology.

Still only visual observations were possible. Visual instruments (like the backstaff) were introduced for long distance navigation and geodesy (like the quadrant). The religious calendar (esp. Easter) demanded more precise time keeping. In 1572 Tycho Brahe observed Stella Nova (now: Cas A) one of the clear deviations of Aristotles’ model. The parallax was unmeasurable, putting it beyond the Moon, where no change was to be expected.

The invention of the telescope in 1608 opened the universe for direct observation. At first singlet refractors were used. But reflectors (with bronze mirrors), with no chromatic aberration, soon became popular. Vd Bilt Gregory reflectorAfter discovery of the achromatic lens in 1750 the refractors returned. The seventeenth century was spend on scrutinizing extended objects (like planets and comets), mapping the sky (astrometry), and applying celestial mechanics. For navigation star catalogues (like those of Flamsteed) were made. However the clocks of Harrison replaced the astronomical time keeping on ships.
The end of the eighteenth century and the beginning of the nineteenth were exciting times. In 1790 Hershel discovered Uranus, in 1801 the first asteroid (Ceres) was discovered. Calculation orbits in the solar system and double stars was fully developed. Kaisers’ early career was launched by his computation of the orbit of the comet of Halley.Comet seeker Kaiser A bit later (in 1838) Bessel measured the parallax of 61 Cygni; for the first time putting a scale on the universe beyond the solar system. A few years after that (in 1846) Neptune was discovered, as a triumph of classical mechanics. Astrometry became the central activity of astronomers during these times, with good telescopes and good clocks. Two developments determined the next steps:
1. Photography. Started by Niepce in 1826, while in 1854 the first picture of the Moon was taken.Moon 1854
2. Spectroscopy. Started in 1860 by Bunsen en Kirchhoff.
Also physics and chemistry got their modern footing in this century. Kaiser was aware of the potential of Photography (his son wrote his thesis about it), but did not live long enough to see dry emulsions which were sensitive enough. Kaisers’ academic background was also too narrow to judge physics. So Kaiser focused on his transit circle.
His successor H.G. v.d. SandeBakhuyzen went along the same lines. He completely missed the astrophysical revolution, considering it a passing phenomenae. The transit circle was used for visual measurement of stellar positions. Contributing to the FK, and to the AGK zone catalogi in (1870-1900). On government request he also contributed to geodetic mapping. Leiden did not participate in the big photographic all sky mapping project, called Carte du Ciel (started 1887, 22,000 glassplates) and it’s associated Astrographic catalogue. Vatican 1904The Carte du Ciel was not more than half completed and a total failure. The Astrographic catalogue was completed, and little used, until it was used as base for the Hipparchos project. Kapteyn in Groningen however took up photography and published (with Gill) the Cape Photographic Durchmustering Photographic Durchmusteringin 1875. This completed the standard Bonner Durchmusterung (1862) of the northern hemisphere. Bakhuyzen did indeed enter the photographic area in 1897 by installing the astrograph (“Fotograaf”). This instrument was a 1½ scaled up version (F15, 40”/mm) of the Carte du Ciel refractors (F10, 1’/mm). It was meant for parallax determinations, but already too small for that purpose when ordered. The observatory connected again to the main stream of astronomy with the appearance of de Sitter and Oort, two students of Kapteyn, and of Hertzsprung.