We first talked at the first meeting about our cosmic address (our place in the Universe), and put the Earth in context. We have to use exponentials (powers of ten, expressed here by "^") to express the very large range of scales involved.
We can make 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 can also use a scaling to discuss our place in the history of the Universe, which had a definite beginning somewhat 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 (expressed as powers of ten) of space and time we use in Astronomy. For more on how to express numbers, and a primer on the precision you should use, go here.