Scale
As you contemplate the scale of the Universe, and the steps that takes you to the observable outer reaches of the Universe, remember that we could likewise construct a multi-step program to smaller scale things. During the course, we will be discussing elementary particles like protons, which have a "size" on the order of 10^-15 (E-15) meters. The use of this type of notation, known as exponential notation, is essential for astronomy. If you need to, review the use of exponential notation (appendix A) and the rules associated with multiplication and division. The main goal of chapter 1 is to introduce you to many of the types of object you will be studying in this course. The Universe seems to be organized into groups of galaxies, and each galaxy contains many stars and much gas and dust. The organizing force is gravity, and next week we shall go over the science of the gravitational force, which is about 300 years old – about 70 years younger than the modern model of our solar system. Another important point mentioned in this first chapter is the concept of evolution. Galaxies are moving further apart as time goes on, and these galaxies (as well as the individual components like stars and planets) are changing as well. Astronomy IS about evolution - not just the evolution of life, but the evolution of everything. Ultimately, you will know how astronomers explain the origin and evolution of everything except life - all elementary particles, galaxies (still pretty tentative), stars, planets, and chemical elements. Some big questions remain, however, and are the subject of ongoing research. Two of the hottest topics in recent years are:

1. the nature and amount of "dark matter," stuff that makes up most of the mass of the Universe but which we cannot detect except by its gravitational influence on something else, and
2. the origin of "dark energy" that apparently is causing the universal expansion to speed up.

Organization
In a modern astronomy course, the names and locations of constellations receive little attention for their own sake. The motion of our own observing station - Earth - along with the brightness of our Sun, dictate what constellations are visible to us in the progress of a year. Many of the actual photographs of astronomical objects in your book will mention the name of the constellation in which it resides, and you can then use a star chart with constellation maps to know where to look for these objects. Sometimes, you can see fuzzy patches with binoculars that correspond to the colorful pictures in your text, which were taken with really large telescopes and very expensive cameras. One key point to remember is that stars in a constellation are NOT generally the same distance from us. The real Universe is 3-dimensional, but our view of it is 2-dimensional (our depth perception technique does not work for very large distances). Thus, the brightest stars in Orion are not necessarily the closest. Try to understand the conceptual difference between "apparent magnitude" and "absolute magnitude". These types of terms will pop up many times during the course. Another key concept is that of angular location - how astronomical objects are located. For describing the location of objects in the sky we use a system that has been in use for 2000 years, and it is based on assuming that the Earth does not move or spin on its axis. If you ever want to locate a star based on locational data, you will need to consult a more detailed book on this subject - one that defines the equivalent to Earth’s latitude and longitude. The corresponding angles for stars are "declination" and "right ascension" respectively. See other textbooks in the library for definition of these terms. The main thing to remember now is that we locate stars using angular measure, which begins with units of "degrees" (360 degrees in a circle). The degree is then subdivided into arc-minutes (60 arc-minutes per degree) and arc-seconds (60 arc-seconds per arc-minute). As you probably know, Polaris, the "north star," is a good reference point for northern hemisphere observers - it moves very little through the night. It will not be a good reference point in a few thousand years after Earth’s axis has precessed.

Motion
I am guessing that many of you studied some of this material somewhere in the junior or senior year of high school. If so, you might recall that our seasons are the result of Earth’s tilted axis of rotation - that is, the axis is NOT exactly perpendicular to the plane of Earth’s orbit around the Sun. Additionally, Earth orbits the Sun in an elliptical path (can you construct an ellipse with a string and 2 pins?), with a period of 365.25 days. The Moon orbits Earth (also in an elliptical orbit), and a very curious coincidence leads to some interesting visual effects known as eclipses. The angles subtended by both the Moon and the Sun (from Earth) just happen to be about the same (about 0.5 degree), so the possibility exists of observing eclipses of both Moon and Sun. We do not see eclipses more often than we do - because of the tilt of Moon’s orbit around Earth relative to the orbit of Earth about Sun. Let me know if the book’s explanation needs some help on this matter.