Introduction to Astronomy (II)

Hi there IntroAstro!

We are starting our second week, thought I would share some thoughts about the class.  

Our first week dealt with the way things move in the sky.   The mental gymnastics involved in seeing things simultaneously in three mutually rotating coordinate systems are always challenging.  The reward for sticking with this, though, is understanding what goes on around us. Thinking in this way is not something that comes naturally to most of us, and becoming comfortable with it takes time - both work time and chronological time. If you still find some of the material confusing you are in good company.  The good news is that, with time, it should become clearer.  Also, while we will start off the second week from where we left off the first, most of the rest of the class can be done quite independently of the material from this week, although thinking in three dimensions (and in time) is a skill we will need - and continue to develop - because that is where (and when?) we live.

If nothing else, you should have developed a healthy respect for the early workers in the field who worked out all of this without simulations, or calculators, or even slide rules!

This second week we start where we left off - adding ingredients to our model of the Universe.  Very soon we find that a two-dimensional planetarium show projected on a “very large” celestial sphere is not a good enough description.   Tearing the planets - and, in two weeks, the stars as well, out of the celestial realm and into a three-dimensional, physical universe is one of the remarkable achievements of humans, and we will be able to follow much of the thought, if not the detailed computations, that go into this.

Understanding planetary motion will naturally lead us - both historically and intellectually - to Newton’s mechanics and his theory of gravity.   We will not be thorough, but will hopefully work 

enough examples to get what we need for our purposes.  The rest of the week throws history aside and rushes us through a selection of the insights that followed - with a few centuries’ hard work by some very brilliant scientists - from Newton’s ideas.  We will use examples from astronomy to demonstrate what we are talking about, but the topic will be physics. We are gearing up for our assault on the Universe, this will be time well spent.

If you have never taken a physics class, this will be a lot.  If you have, some of it may be a repetition of things you know.  We have an amazing diversity of backgrounds and interest in this class, and we try to strike some balance so everyone can get something from it.  Some of the clips this week are long.  Too long.  This will not happen again - as you know I am learning how to do this as I go.  I recommend using in-video quizzes as natural break points at which to stop, go do something else, and return after letting the material “settle” a bit.  Few of us can focus on a one-hour video.   

Some of the algebra will be more involved than last week, but typically students find the material less difficult.  In general, in my experience the first week is often the toughest for many students.  In part this is because of the geometric complexity.  In part it has to do with becoming comfortable with thinking in the way physicists do.  This too takes time, but I think it can be the most rewarding part of this class.  What this involves is learning to look at a problem, a system, a situation, and discern what is going on.  It is not (in this class) a matter of performing some incredibly complex calculation.  It’s more a matter of struggling to figure out how the mathematical expressions relate to the problem at hand. 

One of the most exciting things, for me, was to watch the forums and observe how students with such diverse backgrounds - in astronomy and beyond astronomy - interacted.  There were a lot of good, substantive discussions of issues related to class at all levels, and there were a lot of great discussions of issues unrelated to class as well. The opportunity to share the learning experience with a large, diverse community and to profit from each other’s insights is a wonderful feature of this mode of teaching, and many of you seem to know how to use it. 

This class is a pioneering experiment.   I don’t know if anyone knows how to do it right, I know I am just learning, and I appreciate your patience.  I also appreciate the many useful suggestions and ideas in your comments. I am still (gasp!) recording video for the class and will try to implement some of these.  Please keep them coming!

Ronen Plesser, Duke University