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Double Shadow Transits of the Galilean Satellites of Jupiter
Question: Why is there a double shadow transit (i.e. of the Galilean moons) season for Jupiter and why does it occur during the opposition of the Jupiter relative to Earth? Do DST occur all the time, but during opposition, it is more apparent to us on Earth? — Grace
Answer: Double Shadow Transits (DST), or the shadow of two Galilean satellites on the cloud tops of Jupiter, occur during Jupiter opposition due to the relative alignment of the Sun, Earth, and Jupiter during opposition. Jupiter opposition makes these events visible to us on Earth, but in fact Galilean shadow events can occur any time that a Galilean satellite passes between Jupiter and the Sun as viewed along a line connecting the Sun and Jupiter.
Jeff Mangum