Astronomy 1122H Lab 16Sizes & Masses of Pluto & CharonNames ____________________________________________________________Pluto and its moon Charon are very distant from Earth and very difficult to study. However, it wasessential to determine their basic properties from Earth before a spacecraft could be sent there forclose-up study.In this lab, you will use Earth-based observations todetermine the sizes of Pluto and Charon. Thisresult can then be combined with their estimated densities todetermine their masses.This isessential information to begin our understanding of these worlds.Do not get lost in the calculations butfocus on understanding the concepts; be sure touse scientificnotationandshow all work.Part 1 – Size of Pluto and CharonBecause Pluto is so far away (30-50AU!), directly measuring its angular size is not possible.But during the 1980s, Charon’s orbit around Pluto appeared edge-on from Earth; in other words,Charon and Pluto appeared to eclipse each other(Figure 1). Knowing the orbit of Charon, theseevents would enable us to measure the sizes of these worlds.Figure 1:Charon’s orbit around Pluto resulted in eclipses.
In Figure 2 below,First contactoccurs when the edge of Charon first touches the edge of Pluto.Second contactoccurs when Charon completely disappears behind Pluto.Third contactis when the leading edge of Charon reaches the other edge of Pluto.Fourth contactis when the trailing edge of Charon just leaves the edge of Pluto.The length of time between these events depends on two factors: thevelocityof the satellite and thediameter of both bodies.The time interval between first contact and third contact (when Charon emerges from behind Pluto)depends on the moon’s velocity and the diameter of Pluto.We can measure these time intervals anduse the known velocity of Charon to measure the diameter of both Pluto and Charon.