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Orbital Mechanics. Historical Perspective. What is an Orbit. O rbit refers to the motion of one body around another Although not always the case, one object is typically very large in relation to the other
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Orbital Mechanics Historical Perspective
What is an Orbit • Orbit refers to the motion of one body around another • Although not always the case, one object is typically very large in relation to the other • In this case, the smaller object is said to orbit around the larger, and the larger is typically presumed to be fixed in space
What is a Satellite? • Today, we typically think of a satellite as something man-made that orbits the Earth • This is true, but anything that orbits another body is a satellite • The planets in our solar system are satellites of the Sun • The Moon is also a satellite of the Earth
History of the Study of Orbital Mechanics – Ancient Greece • Interest in orbital motion dates at least to ancient Greece • Aristotle studied the motion of the planets in the night sky • General understanding at the time was that the Earth was fixed in space and the heavenly bodies moved around it
History of the Study of Orbital Mechanics – Copernicus • Nicolaus Copernicus (1473-1543) • First to theorize that the Earth and other planets actually revolved about the Sun • Assumed the motion to be circular • Took accurate measurements and found that his assumption was not strictly accurate • Theory was considered heretical at the time
History of the Study of Orbital Mechanics – Brahe • Tycho Brahe (1546-1601) • Lectured at University ofCopenhagen • Responsible for gathering a wealth of accurate planetary motion measurements
History of the Study of Orbital Mechanics – Kepler • Johannes Kepler (1571-1630) • Assistant to Brahe • Proposed that planetary orbitswere elliptical • Proposed laws of orbital motion that are still used today
History of the Study of Orbital Mechanics – Hooke • Robert Hooke (1635-1703) • Member of the Royal Society • Debated Newton on factsabout orbital mechanics
History of the Study of Orbital Mechanics – Newton • Isaac Newton (1643-1727) • Grew interested in mathematicsfrom reading about astonomy • From Kepler’s work, deduced the existence of an inverse square law attractive force • Proposed Theory of Universal Gravitation • Wrote Principia, considered the greatest scientific book ever written • Posits his three laws
Conclusion • Interest in orbital motion dates back to ancient history • First formal assertion that the earth was not the center of all things in mid-16th century • Study of orbital motion led directly to Newton’s Principia and the three laws
Conclusion • Study of orbital motion from 16th century until Newton focused on how the planet orbited the Sun • Newton proposed why the planetary orbits exhibit the behavior they do with the Theory of Universal Gravitation • Kepler’s and Newton’s laws govern our understanding of orbital mechanics still today