SDSU ASTR 310 "Astrobiology"
2020 Spring Semester    				      Prof. Welsh

			Answers for Written Homework #1

PART I.
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Chapter  1, #11: b
Chapter  1, #14: b
Chapter  1, #17: c

Chapter  2, #36: c
Chapter  2, #38: b

Chapter  3, #35: a
Chapter  3, #39: c
Chapter  3, #40: c

Chapter 11, #38: b
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PART II.
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Chapter 3, Quantitative Problem #58 "Moon to Stars" (on page 102)
"How many times greater is the distance to Alpha Centauri (4.4 light-yerars) 
than to the Moon? What does this tell you about the relative difficulty of
sending astronauts to other stars compared to sending them to the Moon?"


There are several ways we can do this problem, but the key to all of them is
to have the distances to the Moon and Alpha Centauri in the same units. The
units can be km, miles, light-years, cm, cubits,... it does not matter, as
long as we are consistent. 

One logical approach would be to convert all the distances to kilometers.
One light-year is 9.46 x 10^12 km (see p. 58 or Appendix A to get this number).
Then we have Alpha Centauri being at a disance of
d = 4.4 light-year * (9.46 x 10^12 km / light-year)
d = 4.16 x 10^13 km.

The Moon is only 384,400 km away (see Table E3 in the Appendix).

So then the ratio of the distances is 4.16 x 10^13 km / 384,400 km
= 1.08x10^8. Rounding this to two significant digits gives 110,000,000.

Thus Alpha Centauri is about 110 million times futther away than the Moon!
Sending astronauts to Alpha Centauri is currently an impossible task.

Note: Alpha Centauri is our nearest star (system). Travelling to other stars
would be even more difficult.

. . . . . . .

Here's another way to do this problem:

Instead of using kilometers, let's use the speed of light and a clock
as a tool. Alpha Centauri is 4.4 light-years away. That means it takes
light 4.4 years to get there.
From our discussion in class, the Moon is about 1.25 light-seconds away;
it only takes 1.25 seconds for light to get to the Moon.

So to see how much longer it would take to get to Alpha Centauri compared
to getting to the Moon, we divide the two times:

ratio of time = 4.4 years / 1.25 seconds.

But the units don't work out, so we have to convert years to seconds. 

Multiply the number of seconds in a minute times the number of minutes 
in an hour and times the number of hours per day, then by the number 
of days per year. There are 86,400 seconds per day and 365.25 days per 
year, so that comes to 31,557,600 seconds per year. So,

ratio of time = 4.4 years * (31557600 seconds/year) / 1.25 seconds.
ratio of time = 111,082,752

Rounding this to the correct number of significant digits gives:
ratio of time = 110,000,000

So it would take about 110 million times longer to get to Alpha Centauri
than it would to get to the Moon! That's a heck of a lot longer!


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PART III.
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Astrobiology Magazine 
Review and Personal Reflection

Each article is different and the reflections are individual, so there 
is no unique answer. However, there are some very basic requirements 
that you need to have to earn full credit:

- the article must have been published after March 2019.
- must list the title
- must list the date
- must list the full web address (the URL)
- must list the author, if there is one
- no spelling errors
- no grammar errors