Astronomy 105G Lecture Notes, 14 January 2004

Announcements

• Reading: Prologue of textbook
• Homework 1 due Wed. Jan. 21, 10:30 am
• SIGN UP FOR A LAB SECTION IF YOU HAVE NOT ALREADY DONE SO

Introductions

• I (Dr. Chanover, the professor) introduced myself
• the teaching assistants, Sarah Bates and Jim Norwood, were also introduced. The TA's will be your instructors for the lab, and will help out with grading and lecturing in my absence.
• the locations of lab were described (Science Hall on Mondays (both sections) and O'Donnell Hall on Tuesdays)

Syllabus

• The syllabus was passed out and explained in detail. If you need a copy of it, you can access it here.
• please make note of: cell phone use policy, late homework policy, and attendance policy

Why New Mexico is a Great Place for Astronomy

Lucky you! You have enrolled in an astronomy class at a university that has a terrific astronomy department. Our faculty do research on a variety of astronomical topics, including planetary science. The southwest is an especially good place for observational astronomy because we have relatively little light pollution (compared to New York or Los Angeles) and because we have many clear nights and a dry climate.

What We Will Study in This Class

When we look up into our sky, there are many different kinds of objects that we can see. These include:

• stars
• the Moon
• planets
• comets
• artificial satellites
• galaxies
• the Milky Way
• the Sun

For nearly all of this class, we will study only objects in our own solar system. Thus, we will restrict ourselves to planets, comets, asteroids, and the Sun. We will define all of these objects in more detail next time.

The Language of Astronomers

In astronomy, most of the time we deal with very large numbers. This is because the distances and sizes of most objects we discuss are very large. In order to abbreviate very large (or very small) numbers, we use scientific notation. This allows you to write a big number as N x 10^m, or "something times ten to the something." The way to rewrite a large number in scientific notation is as follows:

• put a decimal point after the first non-zero digit of the number
• count how many places you have to move to the right after the decimal point to get to the end of the number, and put that result in the exponent

Thus, we can rewrite the number 250,000,000 as 2.5 x 10⁸ because we put the decimal point after the first non-zero number (2), and then move over 8 spaces to the right to get to the end of the number.

We will go over how to write small numbers in scientific notation next time.

Astronomers tend to use metric units (kilometers, meters, centimeters, grams) instead of the English units that you are probably more familiar with (inches, feet, miles, pounds). This makes calculations easier since all metric units are based on powers of ten. We will try to use exclusively metric units in this class, although I will convert numbers to English when necessary.