by JohnD » Wed Nov 28, 2012 5:23 pm
neufer,
I can't square your answer with geometry. The distance of Io from Jupiter is irrelevant.
At the orbit of Jupiter, the Sun's rays are as near to parallel as dammit.
So the distance Io moves daily in its orbit is the same as the distance moved on the 'surface' of Jupiter, increased as the shadow moves away from directly under the Sun, and decreased as the shadow moves from the limb of Jupiter towards its centre, by the Tangent of the angle of the sun above the horizon.
That difference would not be visible from Earth at opposition, when we are looking along the Sun's rays, although it should be if we could see Jupiter 'from the side', with an obvious terminator. Do we ever see it that way, except from Galileo?
I'll gladly accept your point about the pictures being taken some time before true opposition. If the angle of the Sun was so great in relation to the angle of view from Earth that Io's shadow is so displaced, should we not see the terminator at the edge of Jupiter's disc, peeping around it by a similar amount?
John
neufer,
I can't square your answer with geometry. The distance of Io from Jupiter is irrelevant.
At the orbit of Jupiter, the Sun's rays are as near to parallel as dammit.
So the distance Io moves daily in its orbit is the same as the distance moved on the 'surface' of Jupiter, increased as the shadow moves away from directly under the Sun, and decreased as the shadow moves from the limb of Jupiter towards its centre, by the Tangent of the angle of the sun above the horizon.
That difference would not be visible from Earth at opposition, when we are looking along the Sun's rays, although it should be if we could see Jupiter 'from the side', with an obvious terminator. Do we ever see it that way, except from Galileo?
I'll gladly accept your point about the pictures being taken some time before true opposition. If the angle of the Sun was so great in relation to the angle of view from Earth that Io's shadow is so displaced, should we not see the terminator at the edge of Jupiter's disc, peeping around it by a similar amount?
John