Passage IV
As viewed from Earth, Jupiter’s 4 largest moons—the Galilean moons—appear to move relative to Jupiter along an east-west line. The farther from Jupiter a moon appears to be, the greater its angular separation, θ. Figure 1 shows these moons’ positions at midnight on a certain day in June 2012 as viewed from Earth (top section) and as viewed from above Jupiter’s north pole (bottom section).
Figure 2 shows θ for each moon from midnight on June 20, 2012, to midnight on June 28, 2012. For each moon, 1 wave cycle represents 1 orbit around Jupiter. (The time to complete 1 orbit is the time between any 2 consecutive peaks or any 2 consecutive troughs.)
Figure 2 adapted from Sylvain Rondi. Jupiter Version 2: Programme gratuit de calcul d'éphémérides des satellites galiléens de Jupiter ©2009 by Sylvain Rondi.
25. According to Figure 2, at which of the following times in 2012 was the angular separation for Callisto closest to 20 arcsec east?
Your Answer is
Correct Answer is D
Explanation
Looking at figure 2, it can be found that Gallisto’s position at midnight on the 24th and 28th is close to 20 arcsec east, and the time points given in the photo selection, the closest to this position should be 6 pm on the 27th