### ISP 205 Lab 5 Discussion Questions

1. Today in lab, we learned how to use parallax to measure distances. Is there a limit on how far away we can measure distances using paralax, and if so why is there a limit? Why did it take so long to first measure a stellar parallax (1838) when the idea of parallax has been around since the time of Aristotle (~350 BC)?

2. Copernicus knew that no parallax was observed for any star (at the time he lived), yet he still proposed his theory that the Earth orbited around the Sun. What do you think his thoughts might have been to the contradiction between his theory that predicted stars should show parallax and the fact that none had been observed?

3. In 1989, the ESA (European Space Agency) launched the satellite Hyparcos to measure stellar parallaxes. Why do you think stellar parallaxes made from space are better than those made from the ground? Would there be an advantage or disadvantage to measuring stellar parallax from a space-based telescope at a larger solar orbit, such as that of Jupiter (orbital radius 5 AU)? If this space telescope could only make parallax measurements of 0.05 arc seconds or greater, what is the distance of the most remote stars that could be determined accurately (about 10% or better)? How much larger of a volume of space would be covered compared to a similar space-based telescope orbiting around Earth? How many more stars would be included in this volume of space?

4. Do you think the method you used to find the height of the Beaumont tower would work for the Sears Tower in Chicago? Why or why not. How would you have to modify the equations to make it work if not?

5. What do think it would mean if the parallax of a star were changing over time? What does it mean if the angle is getting larger or smaller?

6. If you measure a parallax of one arc second for two objects that are ten miles apart, how far are you from the objects?

7. A pair of stars located at nearly the same position in the night sky is called a double star. If the two stars are actually orbiting each other, they are called binary stars. A visual binary called "70 Ophiuchi" has a period of 87.7 earth years and a semi-major axis of length 4.5 arc seconds. The parallax of the system is 0.2 arc seconds. What is the combined mass of the two stars?

Updated: 2002.09.11 (Wednesday) 10:12:57 EDT