1. To calculate the dashed orbits from the stellar positions,astronomers had to assume that __________.

a)thestars are all main-sequence stars

b)ifthey observed for many more years, the dots would trace outellipses

c)ifthey observed for many more years, the dots would trace outparabolas

d)thecentral object has a mass of about 4 million solarmasses

2.Noticethat some of the stars on the diagram are represented by a seriesof dots that are very close together, while others have their dotsfarther apart.

Keeping in mind that all the stellar positions were measured atone-year intervals, which stars are movingthefastestintheir orbits during the time period indicated by thedots?

The fastest stars are the ones with _______________.

a) the dots closest together

b) the most dots

c) the dots farthest apart

3.Todetermine the mass of the central object, we must apply Newton'sversion of Kepler's third law, which requires knowing the orbitalperiod and average orbital distance (semimajor axis) for at leastone star.

Let's consider the star with the smallest orbit, which isrepresented by red and pink dots. What is the approximate orbitalperiod of this star?

a) 5 yr

b) 13 yr

c) 20 yr

d) 100 yr

4.Lookagain at the orbit of the star with the smallest orbit, representedby red and pink dots.

By comparing the orbit to the scale bar shown on the diagram, youcan estimate that this orbit has a semimajor axis of about_____.

a) 12 AU

b) 200 AU

c) 800 AU

d) 1600 AU

1,600 AU 0.2" central object