Short Questions about the Solar System

1. The solar system rotates quite fast with all the planets going around the sun on time scales of years. The clouds of gas and dust we see in the galaxy that are probably going to form new solar systems are rotating so slowly we can barely detect it but we are sure they are rotating a little bit. Describe how the change to fast rotation probably occurred as our solar system was being formed. You may wish to use the analogy of a spinning figure skater or a child moving on a roundabout.

2. There appears to be little in the way of junk left in the solar system within the orbits of the giant gas planets except the asteroid belt. By junk I mean other asteroids, mini-planets or mountainous chunks of ice similar to comets. From the craters on the moon and elsewhere we think that there was probably a lot of junk around in the early solar system. Describe what we think happened to any junk that didn't hit something directly.

3. Historically astronomy was limited to visible light; meaning light we can see with our eyes.
Visible light is still particularly important for astronomers on the ground even though we have electronics that can detect all sorts of other wavelengths of light we cannot see with our eyes.
What is it about Earth's atmosphere that makes visible light more useful than most other wavelengths of light for astronomers on the ground?
Note: The answer you give should have nothing to do with whether we can see particular type of light using our eyes.

4. Brightness and Radar measurements. Suppose we have a radar dish that generates a strong signal that travels out to hit an asteroid 109 kilometres away.
(a) How would the brightness of the radar signal arriving at the asteroid change if the asteroid was moved twice as far away?
(b) How would the brightness of a signal originating at the asteroid and detected back on Earth vary if the asteroid was moved twice as far away?
(c) In the radar experiment the asteroid reflects that part of radar signal that arrives at it back in all directions. In this way it is behaving like a weak source of radar signals. The part of the signal comes back to the original radar has a brightness of 81. The lowest signal we can detect has a brightness of 1. Determine the way the strength of the detected signal varies with the distance that the asteroid is away from the radar dish. What is the furthest an asteroid of the same size and other characteristics could be away from us before we could no longer use this radar equipment to measure the distance to it?

5. Examine the table. Which planets would float if you dropped them in the Sun? Which would float if you dropped them in water? Which would sink fastest?

6. How many sets of planets would you need to create the mass of the Sun?

7. What do the orbits of the planets and satellites tell us about the rotation of the cloud that formed the solar system?

8. The speed of light is 300,000 kilometres per second. This number isn't easy to get a feel for but it's good it's so fast because it allows us to see things instantly on Earth without waiting for the light to arrive.
The Sun is far enough away that light takes an appreciable time to travel to us. Assuming the sun is 150,000,000 kilometres away, how long would it take us to realize if the sun suddenly stopped shining?