Alfred Wegener: Difference between revisions
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Astronomy and meteorology were then parts of the same subject. One had to consider atmospheric conditions in every astronomical observation, and especially carefully in positional astronomy, where one was trying to determine where something was as much as what it was. These atmospheric influences meant that would-be astronomers had to learn how to measure and record temperature and humidity to correct for their effects. Moreover, weather prediction and prognostication was also useful to an astronomer. A falling barometer, high cirrus clouds at noon, and a wind backing from the south to the northwest were strong indications in Heidelberg that an evening planned for astronomical observation might well be spent instead working in the darkroom.
=== Winter Semester 1900 - 1901 ===
Alfred traveled at the end of the semester from Heidelberg to die Hütte, for some vacation time with Kurt, Tony and his parents. It was time to hike and talk with Kurt and plan for the second year at Berlin. Kurt was progressing well in meteorology at the Technische Hochschule in Charlottenburg. Perhaps because of Kurt's account of these experiences, as well as Alfred's own introduction to the subject from Max Wolf in Heidelberg, Alfred thought about adding meteorology to his program.
The schedule Alfred planned for the winter semester of 1900-1901 was more rigorous than that of his first year. The mathematics course was differential equations with Lazarus Fuchs, general mechanics with Max Planck, older theories of celestial mechanics with Julius Bauschinger, general meteorology by Wilhelm von Bezold, geographical position finding and celestial navigation with Marcuse.
==== Mechanics ====
General theoretical mechanics is a unified approach to physics through concepts of motion. Students began with the development of a physics of force and Newton's laws of motion. This treatment was then extended to the ideas of work, energy and the "conservation laws", particularly the conservation of momentum and the conservation of energy. Such a course usually ended with a physics of energy based on the formulation of Joseph Louis Lagrange and William Rowan Hamilton. Along the way, students were introduced to the mathematical treatment of classical problems : central-force motions, the orbits of planetary bodies, oscillations, harmonic motions, the motion of rigid bodies -- where the objects treated are no longer considered as point masses with a location only, but have a shape and an orientation.
==== Celestial mechanics ====
Julius Bauschinger specialized in the field of determining the orbital paths of heavenly bodies. He fitted in well at Berlin, where many people worked on the measurement and calculation of locations, orbits and distances; the calculation of ephemerides (planetary tables); and the refinement of methods for correcting observational errors.
Bauschinger's "older theories of celestial mechanics" course began with Johannes Kepler, who made the first determination of the laws of planetary motion, and Issac Newton, who had spent much effort on determination of cometary orbits. It then passed through the elaboration of celestial mechanics by Pierre Simon de Laplace, Joseph Louis Lagrange, Wilhelm Olbers and finished with the methods of Karl Friedrich Gauss. In all, it covered the period from 1600 to about 1850. This approach allowed Bauschinger to develop the course as a history of orbital calculation and error reduction. He was in the midst of writing what would become the standard text of orbital determinations, "Die Bahnbestimmung der Himmelskörper" (1906). He was also spending much time documenting the history of the field in Germany and producing translations of hard-to-find earlier works.
The fundamental problem in this branch of celestial mechanics was to find the orbit -- and thus the position relative to Earth at any given time -- of an object -- such as a comet or an asteroid that was moving around the Sun -- and to find it with a minimum number of observations -- usually three. Restricting observations to the absolute minimum also minimized the immense amount of trigonometric calculation required to solve the equations involved in the problem. One took the celestial latitude and longitude (the right ascension and declination) of a celestial object on three successive occasions. Then, using these coordinates and the time of observation, generated a total of nine equations that had to be solved for nine unknowns.
There were three principal approaches to this problem, all treated in Bauschinger's course. Each approach had strengths and weaknesses, depending on the character of the orbit being studied, especially its eccentricity and the number and character of perturbations. "Take three observations of an asteroid not separated from one another by more than 15 days, or three of a comet not separated from one another by more than 6 days, and compute the elements of the orbit by both the method of Laplace and also that of Gauss."
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