食

Rēmā ga Mokusei no eisei no hitotsu de aru Io no shoku no shūki o sokutei shita tokoro, ittei de wa naku, Chikyū no kōten ni tomonai hendō suru koto ga wakarimashita.When Rømer measured the period of the eclipses of Io, one of Jupiter's satellites, he discovered that it was not constant but fluctuated with the Earth's revolution.