Chapter 01 Part 1 Our Place in Space
We all wonder It is a very human trait to wonder where we are in this universe. Usually, the only hint of the vastness of the universe comes at night. There seems to be so much up there how can we not wonder?
Time, Space, and Movement One of the brilliant things about physics is that all three things in the title above are tied to each other. Movement takes time, which we can see. Space is mostly empty, but the light moving through it shows us movement (over time!)
Time and the Universe Figure 1.10 is great what a way to think about the universe s history. If the universe s age was a year The Earth appears on August 13 Life on Earth appears on Dec 13 Dinosaurs appear around X-mas And humans appear on New Year s Eve! The universe is much, much older than we can ever possibly understand. And during that time, a lot of very weird things have happened in the universe.
The Size of Space The universe is big and very, very weird. It is good to get started figuring out the weirdness locally and then move outward. This is interesting (but don t worry about getting g all the details about the planets) - check out one of the following (they are both the same info): 1.2 The Scale of the Universe from your book 1.2 The Scale of the Universe from your book s CD
Just how big is vast. It is hard to remember we are in a big universe: From a dark spot, 5 planets are visible to the eye. From a dark spot, the night sky has about 6,000 stars visible to the eye. Our galaxy has 100 billion stars. From a dark spot, 4 galaxies are visible to the eye. There are at least 100 billion galaxies in the universe. These numbers are completely beyond our ability to comprehend. The universe is irrationally large!
Can we see the entire universe? Yes, we can, but the more distant objects are so far away that the light coming to us came far in the past! So we can see it all, but all in the past.
How can we know what the universe was like in the past? One of the great things we will learn in Unit 2 is that light travels at a finite speed (300,000000 km/s). Destination Moon Sun Sirius Andromeda Galaxy Light travel time 1 second 8 minutes 8 years 2.5 million years
Example: This photo shows the Andromeda d Galaxy as it looked about 1/2 million years ago. Question: When will we be able to see what it looks like now? M31, the Great Galaxy in Andromeda
The Universe Moves! With a universe so vast and old, it is tempting to think it is too big to move, but it does! Every single thing inside the universe is moving, some slow, some fast, but all move. Let s L look at 2 examples of this movement: The Earth rotates and revolves. The Earth revolves around the Milky Way galaxy (ours) as it revolves.
The Earth Rotates The rotation of the Earth is the daily spin of the Earth about its axis. This is what causes day and night. Try this experiment: Turn a light on in a dark room. Spin around and notice how the shadows fall on your body now you are rotating!
The Earth Revolves The Earth also revolves around the Sun in its orbit. The orbit is not perfectly circular, but it is close. The average distance is 1 astronomical unit (AU). This revolution does not cause the seasons.
The Earth Precesses The Earth s axis is tilted and very, very slowly spins on that tilt. This means that t the North Pole will face towards different stars over time. Ancient Egyptians marked one of the stars of the Big Dipper (Thuban) as the North Star just 5,000 years ago.
Random Motion Inside the Galaxy Space is not orderly all the stars do not move about in an orderly orbit around the galaxy. Most of the stars around us are moving randomly in different directions. This motion is slow, but there is no pattern. Gravitational attraction between stars drives this motion.
Sun s Orbit Around The Galaxy Even the Sun revolves around the core of the galaxy. The average distance is about 28,000 light years (so far that light takes 28,000 years to travel). That revolution takes about 230 million years to complete!
Our Galaxy s Flight in the Universe Even the universe is moving outward. Our best understanding today is that it is expanding outward in all directions at once. So as time goes by, it expands and its bits are all moving apart from each other like raisins in a nice hot cross bun on St Paddy s Day (that was for my Irish wife!).
So, are we ever sitting still? Earth rotates on axis: > 1,000 km/hr Earth orbits Sun: > 100,000 km/hr Solar system moves among stars: ~ 70,000 000 km/hr Milky Way rotates: ~ 800,000 km/hr Milky Way moves in Local Group Universe expands