MDM Observatory Rainbow July 2001
Rainbow over Kitt Peak, Arizona, July 2001 [R. Pogge]

Unit 4: The Physics of Astronomy:
Gravitation, Matter, & Light

All interactions in the Universe are governed by four fundamental forces. On the large scale, the forces of Gravitation and Electromagetism rule, while the Strong and Weak Forces dominate the microscopic realm of the atomic nucleus.

Gravitation binds together all masses in the Universe, governing the fall of an apple and the orbit of the Moon about the Earth. The dance of the planets around the Sun is choreographed by the interplay of gravitational forces. Newton's laws are not mere empirical descriptions, but powerful physical tools we can use to explore the Universe, both figuratively and literally! The first half of this Unit explores gravitation from its first formal description by Newton to how gravity choreographs the dance of the planets in the Solar System.

The second part of the Unit is an exploration of the properties of Light and Matter. Nearly everything we know about the Universe beyond the Earth has been learned from a distance. We cannot directly measure a star, or scoop up a bit of its material to study in a laboratory. We only have to us the light that comes to use from across effectively unbridgable distances. Because light, or more precisely, Electromagnetic Radiation, is produced by and interacts with ordinary matter, what seems at first an insuperable handicap becomes a source of great strength. It is when we began to understand the nature of light, how it is produced and how it interacts with matter, that marked the end of "Astronomy" as a simple cataloging of the heavens as it had been primarily from its very beginnings, and the beginnings of the modern study of "Astrophysics" at the end of the 19th Century.

We end the unit with a discussion of Telescopes, the tools used by astronomers to read and "decode" the message of light from space.


The Apple & The Moon: Newtonian Gravitation (Oct 15)

Orbits (Oct 16)

Tides (Oct 17)

Dance of the Planets (Oct 18)

Quiz 2: Friday Oct 19, in class [Study Guide]

Light the Messenger (Oct 22)

Worlds Within: Atoms (Oct 23)

Matter & Light (Oct 24)

Measuring Light: Spectroscopy (Oct 25)

Telescopes (Oct 26)

Lecture Podcasts Lecture Audio Podcasts

Please see A Note about Graphics if you are curious as to why some of the pictures shown in the lectures are not reproduced with these notes.

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Updated: 2007 October 27
Copyright Richard W. Pogge, All Rights Reserved.