NAKED EYE ASTRONOMY

The simple activity of just watching the sky has produced many significant advances and results over the centuries. It was apparent to the ancients that the motions of celestial bodies, although seemingly random and complicated, were actually quite simple and regular. The relative positions of the stars (grouped together into constellations,e.g., Orion) did not change very quickly; the stars (and other celestial bodies) simply moved in unison making one complete trip around the sky, circling about the point in the sky roughly where the North Star (Polaris) currently resides, once every 23 hours 56 minutes and 4.091 seconds (the sidereal day). The stars rose in the east and set in the west.

This regularity led to the first practical use for the early astronomers, namely, Astronomical motions are powerful timekeeping tools. Even today, most of our current time measuring conventions are based on astronomical motions, e.g., the day is determined by the rotation of the Earth, the month is determined by the orbital motion of the Moon, and the year is determined by the orbital motion of the Earth. Furthermore, among the most precise clocks that we have available to us on Earth, are ones based on astronomical motions, e.g., the rate at which stars known as the millisecond pulsars rotate.

The development of modern science started when people tried to understand the regularity of the motions of celestial bodies; an enterprise which took over 2,000 years. The effort culminated in the works of Kepler and Newton; Kepler proposed three laws of planetary motion (Kepler's Laws) which described precisely the motions of the planets while Newton proposed a theory which gave a physical basis for Kepler's laws. Newton proposed: three laws of motion basically a set of rules which allows one to calculate how objects move when subjected to forces; and the Law of Universal Gravitation which described how the force of gravity worked.

When properly applied Newton's laws are very accurate and form the physics which governs the dynamics of most of our everyday experiences. Based on this work and his other contributions, Newton is arguably the greatest physicist who ever lived. However, we continue to learn about the dynamics (motions) of the planets even today. Applying the theories of Newton, a new discipline of physics has developed over the last ten to fifteen years, the study of nonlinear dynamics and, in particular, a phenomenon known as CHAOS. The characteristic of chaos which is of particular interest to us (in this course) is the extreme sensitivity of chaotic systems to small disturbances in their initial conditions.