Astronomy 110: Survey of Astronomy
Homework #1
(Due May 31st, 2005)
1. [Chapter 1, Problem 28] Road trip! Imagine that you could drive your car at a constant
speed of 100 km/hr (62 mph) over any terrain and through any medium (including the
vacuum of space). Remembering that
distance = speed x time
1 yr = 365 days = 8760 hrs
a. How many days would it take you to drive all the way around the Earth (assume the
Earth’s circumference is 40,000 km)?
b. If you started at the Sun, how many years would it take you to reach Earth (the
distance from the Sun to the Earth is 5.8x107 km)? How long would it take you to
reach Pluto (the distance from the Sun to Pluto is 5.9x109 km)?
c. How long would it take to drive the 4.4 light years to Alpha Centauri? (Hint: 1 light
year is approximately 1012 km.)
d. [Bonus] Suppose you want to reach Alpha Centauri in only 100 years. How fast
would you have to go? Compare this to the speeds of the fastest current spacecraft
(around 50,000 km/hr).
2. [Chapter 2, Problem 25] New Planet. Suppose we discover a planet in another solar system
that has a circular orbit and an axis tilt of 35°. Would you expect this planet to have seasons?
If so, would you expect them to be more or less extreme than the seasons on Earth? If not,
why not?
3. A witness is called to testify in a murder trial. The victim was apparently shot to death
during his sleep. The witness, who lives in the country and away from city lights, claims that
she was awoken by the sound of gunshots at 3 a.m. She ran outside to see what the
commotion was about, and when she looked towards her neighbor’s house, which lies due
West of her own house, she noticed a man leaving the premises. Her street does not have any
lighting, but she claims she could see the man clearly because there was a quarter moon
shining above her neighbor’s house, which illuminated the crime scene. Is her testimony
reliable? Why or why not?
4. The Ancient Greeks suggested the Earth was round nearly 2250 years ago and measured its
circumference by observing the Sun. They noted that at the city Syene (point A in Figure 1)
the Sun passed directly overhead on the summer solstice. On the other hand, in the city of
Alexandria to the north (point B), they noted that the Sun came within 7° of being directly
overhead on the same day. They also knew the distance from Syene to Alexandria was 800
kilometers. Using these facts, determine the following:
a. At what latitude is the city Syene located?
b. What is the latitude of Alexandria?
c. What value did the ancient Greeks determine for the circumference of the Earth?
How does this compare to the current value of roughly 40,000 kilometers?
7°
B

A
HINT: Use the Figure to the
left to understand the angles
involved. Remember a circle
has 360° and ratios are your
friend.
Figure 1
5. Optional comments (will not be graded): How long did this homework assignment take you?
Please comment on the assignment and the class in general. For example: Do you feel you
are understanding the material? Do you feel that what you are learning will be beneficial to
you? Other comments or suggestions?