For Your Information (FYI): In astronomy, important information (such as the mass of an object) is derived from moons orbiting planets, planets orbiting stars, stars orbiting other stars (binary stars), stars (like our Sun) orbiting the center of a galaxy (like the Milky Way galaxy), galaxies orbiting within clusters of galaxies, etc. Question 1 encourages you to visualize in 3-d what is happening and familiarizes you with the relationship between velocity, time, and distance.

1. Assume the moon Praxis orbits the planet Kronos in a circular orbit. The moon is 0.1 AU from the planet. It takes 2 years for Praxis to orbit the planet Kronos. How fast is Praxis traveling? Give your answer in meters/sec and miles/hour.
   Hint: the following formulae may be useful:

   • d = v * t
   • circumference of a circle = 2 * pi * R

2. Fill in the blank:
   A mile is a unit of distance. An hour is a unit of time. Miles per Hour is a unit of speed.
   A parsec is a unit of __________________. A lightyear is a unit of __________________.
   

3. What observation did Galileo make which proved that the planets go around the sun? Explain.

4. Why did Aristotle believe that the Earth is round? Explain.

5. Using data from Table E.2 in the Appendix section of your text "The Cosmic Perspective," infer:

   • which planet has no seasons
   • which planets have the largest change between summer and winter.

FYI: Astronomy describes objects of many different distance scales, which tend to use different distance units. This question gives you the opportunity to get familiar with unit conversion and with the distance scale of planets, stars, and galaxies of stars.

1. Using Tables F.1 and G.1 in the Appendix section of your text "The Cosmic Perspective," calculate the distance to the following objects in meters, AU, and parsecs
   

   • The Sun
   • The star Sirius A (this is the brightest star in the Northern hemisphere, known as the "dog" that follows the "hunter", the Orion constellation)
   • The Sombrero galaxy (M104) (distance=50 million lightyears)
   [Hint: Unit conversions can be found in Appendix A.]
   
   For each object, circle which of the 3 units (meters, AU, or parsecs) seems the easiest to use for that object.
   
   Recall the film we watched in class "The Powers of 10". Given the distances you just calculated, approximately how many times further away is the Sombrero galaxy compared to the Sun?
   10⁶ (1 million) times further away? 10⁷? 10⁸? 10⁹ (1 billion)? 10¹⁰? 10¹¹? 10¹² (1 trillion)? 10¹³ times further away?