We first talked about our cosmic address (our place in the Universe), and put the Earth in context. We talked about numbers, and how to estimate the approximate answer to amazing questions.
We did a scale model of the solar system, reducing it by a factor of a billion (10^(-9), or 9 orders of magnitude). This reduced the Sun to the size of a child, and made the Earth the size of a marble sitting about 1.5 football fields away. Saturn is in downtown Berkeley, and the nearest star is more than halfway around the world! We would have to make reductions of another 12 orders of magnitude to bring the Universe down to a similar scale. On the other hand, we'd have to use the same sort of expansion factors to bring the scale of particles relevant to astrophysical processes onto human scales. The movie "Powers of Ten" makes all this rather more graphic.

We then discussed our place in the history of the Universe, which had a definite beginning a little over 10 billion years ago. Check out this interactive timeline which shows the main astronomical events (we'll cover them all this class). If the Universe has lasted for 24 hours, galaxies appear before 3:00am, ours is formed by 4am, the solar system forms at around 3pm, life appears on the Earth by 4pm but doesn't move beyond microscopic forms until 11pm, and humans have been here for less than 1 second. On the other hand, atomic processes take place on timescales that go even more orders of magnitude the other way from 1 second.

We see that the human scale of things is in the middle of the overall scales of space and time we use in Astronomy.

We will use scientific notation extensively - namely exponentials. The exponent indicates the number of places to the left (positive exponent) or right (negative exponent), of the units place the decimal point occurs. Another way to look at it is that the exponent for a power of ten indicates how many zeros would come before a 1 if you wrote the number out. Thus 10^6 (one million) is written as 1,000,000 (or 6 zeros). A negative power of ten means you divide by that number, eg. 10^(-6) is one millionth. If you multiply two powers of ten together, you add the exponents. If you divide them, you subtract the exponents, eg. 10^6/10^2=10^(6-2)=10^4.

Another concept that is useful is the precision of a calculation. If you multiply several numbers together, the answer shouldn't have more than one more decimal place than the number being used that had the LEAST number of places (or precision). For example, 1.2x10^4 times 3.563x10^2 is 4.3x10^6, not (as my calculator says) 4.2756x10^6. In any case, in this class we are almost never interested in numbers to better than 2 decimal places (astronomy is a rather approximate science, for the most part).