24. 다음 글의 제목으로 가장 적절한 것은?
There was once a certain difficulty with the moons of Jupiter
that is worth remarking on. These satellites were studied very
carefully by Roemer, who noticed that the moons sometimes
seemed to be ahead of schedule, and sometimes behind. They
were ahead when Jupiter was particularly close to the earth and
they were behind when Jupiter was farther from the earth. This
would have been a very difficult thing to explain according to
the law of gravitation. If a law does not work even in one place
where it ought to, it is just wrong. But the reason for this
discrepancy was very simple and beautiful: it takes a little while
to see the moons of Jupiter because of the time it takes light to
travel from Jupiter to the earth. When Jupiter is closer to the
earth the time is a little less, and when it is farther from the
earth, the time is more. This is why moons appear to be, on the
average, a little ahead or a little behind, depending on whether
they are closer to or farther from the earth.
* discrepancy: 불일치
① The Difficulty of Proving the Gravitational Law
② An Illusion Created by the Shadow of the Moon
③ Why Aren’t Jupiter’s Moons Observed Where They Should Be?
④ Obstacles in Measuring Light’s Speed: Limits of Past Technology
⑤ Ahead and Behind: Moons Change Their Position by Themselves