"Teach Yourself" Excercises and Hints

Teach Yourself #1
1) Europa is a satellite of Jupiter. It is one of the most important objects in the Solar System for astrobiology.
2) Appendix E in the textbook gives the distances of the planets from the Sun.
3) The time is the distance divided by the velocity. In this case, the velocity is the speed of light, c. Be sure the units of the distance and the velocity are in agreement, e.g., use km & km/s, not km & miles/hour, or km & feet/s, etc.
4) Don't forget to double the time: the signal has to go there and then a reply has to be sent back. So it is a round-trip time.
5) Don't worry about the distance of the moons from the planet, or the distance of the surface of the planet from the core. These make relatively insignificant differences in light-travel time. Do the calculation for yourself and see!


Teach Yourself #2
Write out the Doppler effect formula. Then plug in the values one by one. Start with the left hand side:
a) (lambdaobserved - lambdatrue) / lambdatrue

(653.450 nm - 656.255 nm) / 656.255 nm
-2.805 nm / 656.255 nm
-0.004274

b) The right hand side is = V/c. We want V, not V/c, so bring the "c" over to the left hand side. Then we'll have:
c x {(lambdaobserved - lambdatrue) / lambdatrue} = V

So then put in the numbers:
3x105 km/s x {-0.004274} = V
Now just punch it into a calculator and you've got the answer.

c) So what velocity do you get? Redshift or blueshift?
Click for the answer and another example problem using the Doppler effect.


Teach Yourself #3
In the simplest expanding universe cosmology, the age of the universe is given by: t = 1 / H0.
(Note that a more sophisticated derivation will include correction factors, but we can ignore these to get the gist of the idea that you can get the age from Hubble's constant.)
So start by writing down Hubble's constant.
Then go find the conversion between km and Mpc.
Change all units to either km or Mpc. So you'll have units of
xxx km/s / km (=km/s per km)
or
xxx Mpc/s / Mpc (= Mpc/s per Mpc)
Then the distance units cancel out and you are left with some number with units of (1/seconds).
Take the inverse and you get the age in seconds.
You can work out how many seconds in a year to get the age in years, or just use the approximation that 1 year has about 3.16 x 107 seconds. (For you science/engineer types, a useful approximation to remember is that 1 year is about ~ pi x 107 seconds.).
Now compare your age with the age of the solar system. Is it ok?
Here are some fully worked-out examples using the Hubble law.


Did you know that Mark Twain (Samuel Clemens) was an avid amateur astronomer? Have a look at some quotes about astronomy by Mark Twain.

Teach Yourself #4
For some practice and for guidance to help prepare for the final exam, try answering the questions to a quiz from a previous semester.
I would recommend you don't try these if you are behind in the reading. Catch up first, then try these. Many of these questions come from the biology parts of the textbook and Reader, and from the latter chapters in the textbook.

Teach Yourself #5
Here are some broad questions that will will help you review the course material and also build upon what you've learned in class.

- What is the Rare Earth hypothesis? (Be sure to have read the 2 articles in the Reader on the topic.)
- What is the Fermi paradox? (Textbook Chapter 13.)
- What is Occam's razor? (Chapter 2 and 12)

Also, try these questions in the textbook:
Ch 5 # 30, 33
Ch 6 # 36, 39, 40
Ch 10 # 29
Ch 11 # 27, 28, 29, 30
Ch 12 # 32
Ch 13 # 2, 15, 16, 31, 37, 39
 - Ch 1, Review Question #7, p 24
- Ch 4, Review Question #13, p 110
- Ch 5, Review Question #14, p 142
- Ch 7, Review Question #12, p 201
- Ch 9, Review Question #1, p 243
- Ch 10, Problem #15, p 271
- Ch 11, Review Question #1, p 295
- Ch 13, Review Question #8, p 335

Thanks for taking this course. I hope you (1) learned some interesting things, and (2) had some fun in the process. GOOD LUCK ON THE FINAL EXAM!