# ASTR 109 HOMEWORK #1 (Hamilton) due Wednesday July 23

1. Astronomy makes use of lots of very large and very small numbers. For instance, the mass of the Sun is 2,000,000,000,000,000,000,000,000,000,000 kg while the mass of an electron is only 0.000000000000000000000000000000911 kg. These numbers are hard to work with and even harder to key into a calculator - we need a better way of representing the very large and the very small. The answer is scientific notation which makes use of powers of ten. So the masses of the Sun and the electron are usually written 2*1030 kg and 9.11*10-31 kg, respectively.
a) Go to the scientific notation tool at
http://janus.astro.umd.edu/astro/scinote/ and practice converting between normal numbers and scientific notation until you can do this type of problem in your sleep! Click the "help me" button if you have any trouble. Then take the quiz; print out a copy of your corrected quiz to hand in.
b) Now practice multiplying and dividing scientific notation numbers. See the help file for some examples. When you are comfortable, take the multiply/divide quiz until you get them all right. Hand in a corrected copy of your quiz.

2. The Universe is a big place! To get a sense of just how large it is, go to the Astronomical Distances program at http://janus.astro.umd.edu/astro/distance/.
a) How fast can you make the spaceship travel?
b) At maximum speed, how quickly can you get to the Moon? To Pluto?
c) When we look at a galaxy in the Coma cluster, how long ago did the light that we see leave that galaxy?
d) If you could drive to the Moon and Pluto, how long would each journey take?

3. The Universe is also a very old place. How old? 13.7 billion years! To get a sense of this immense amount of time, go to the Universe Timeline webtool at http://janus.astro.umd.edu/astro/times.html and compress the history of the Universe into one year.
a) On what dates do the Sun, Earth, and Moon form?
b) When does life and complex multicellular life arise?
c) How long did the dinosaurs last?
d) How much time does the entire history of the human race occupy?

4. Finally, go to the class webpage at http://www.astro.umd.edu/~hamilton/ASTR109 and click on the image at the top. The nine planets are displayed with their correct relative sizes and in order of their distance from the Sun.
a) Name the planets in this order.
b) What are the first four planets primarily made of (choose from rock, ice, gas)? How about the next four?
c) What is Pluto made of? You may have heard that astronomers have been arguing about whether Pluto is a planet - why do you think that this is an issue?

Think about these questions and explore the ASTR109 website further on your own!