Cơ học thiên thể
Bách khoa toàn thư mở Wikipedia
Cơ học thiên thể là một nhánh của thiên văn học giải quyết các vấn đề chuyển động và hiệu ứng hấp dẫn của các thiên thể. Lĩnh vực này vận dụng các nguyên lý của vật lý học, cơ học cổ điển vào nghiên cứu các thiên thể như các sao và các hành tinh.
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[sửa] Lịch sử
Mặc dù cơ học thiên thể hiện đại bắt đầu từ 400 năm trước từ thời Isaac Newton nhưng các nghiên cứu trước đó chỉ ra rằng vấn đề về vị trí các hành tinh được biết từ 3000 năm.
Classical Greek writers speculated widely regarding celestial motions, and presented many geometrical mechanisms to model the motions of the planets. Their models employed combinations of uniform circular motion and were centered on the earth. An independent philosophical tradition was concerned with the physical causes of such circular motions. An extraordinary figure among the ancient Greek astronomers is Aristarchus of Samos (310 BC - c.230 BC), who suggested a heliocentric model of the universe and attempted to measure Earth's distance from the Sun.
[sửa] Claudius Ptolemy
Claudius Ptolemy was an ancient astronomer and astrologer in early Imperial Roman times who wrote several books on astronomy. The most significant of these was the Almagest, which remained the most important book on predictive geometrical astronomy for some 1400 years. Ptolemy selected the best of the astronomical principles of his Greek predecessors, especially Hipparchus, and appears to have combined them either directly or indirectly with data and parameters obtained from the Babylonians. Although Ptolemy relied mainly on the work of Hipparchus, he introduced at least one idea, the equant, which appears to be his own, and which greatly improved the accuracy of the predicted positions of the planets. Although his model was extremely accurate, it relied solely on geometrical constructions rather than on physical causes; Ptolemy did not use celestial mechanics.
[sửa] Johannes Kepler
Johannes Kepler was the first to closely integrate the predictive geometrical astronomy, which had been dominant from Ptolemy to Copernicus, with physical concepts to produce a New Astronomy, Based upon Causes, or Celestial Physics.... His work led to the modern laws of planetary orbits, which he developed using his physical principles and the planetary observations made by Tycho Brahe. Kepler's model greatly improved the accuracy of predictions of planetary motion, years before Isaac Newton had even developed his law of gravitation.
See Kepler's laws of planetary motion and the Keplerian problem for a detailed treatment of how his laws of planetary motion can be used.
[sửa] Isaac Newton
Isaac Newton is credited with introducing the idea that the motion of objects in the heavens, such as planets, the Sun, and the Moon, and the motion of objects on the ground, like cannon balls and falling apples, could be described by the same set of physical laws. In this sense he unified celestial and terrestrial dynamics. Using Newton's law of gravitation, proving Kepler's Laws for the case of a circular orbit is simple. Elliptical orbits involve more complex calculations, which Newton included in his Principia.
[sửa] Joseph-Louis Lagrange
After Newton, Lagrange attempted to solve the three-body problem, analyzed the stability of planetary orbits, and discovered the existence of the Lagrangian points. Lagrange also reformulated the principles of classical mechanics, emphasizing energy more than force and developing a method to use a single polar coordinate equation to describe any orbit, even those that are parabolic and hyperbolic. This is useful for calculating the behaviour of planets and comets and such. More recently, it has also become useful to calculate spacecraft trajectories.
[sửa] Albert Einstein
After Einstein explained the anomalous precession of Mercury's perihelion, astronomers recognized that Newtonian mechanics did not provide the highest accuracy. Today, we have binary pulsars whose orbits not only require the use of General Relativity for their explanation, but whose evolution proves the existence of gravitational radiation, a discovery that led to a Nobel prize.