OneOfOne
19-09-2007, 08:19 AM
I was at a public viewing the other night and I was asked a rather interesting question by a kid who was about 10 to 12 years old.
How far from Jupiter are it's moons, compared to the distance between us and our moon? I guess he meant in terms of planet diameters. So last night I did a quick lookup of some stats and came to the following very rough ball park figure.
The Moons orbit is about 30 Earth diameters.
Callisto's orbit is about 12 Jupiter diameters.
So....if you were on another planet viewing the Earth with a magnification that would make Earth appear roughly the same size as you normally see Jupiter, our moon would appear almost 3 times further away from the Earth as what Callisto appears when it is at its furthest separation. With the normal sorts of magnifications (~100x) I use for viewing Jupiter, I can fit all the moons in the view confortably. But at the same image size, the Earths moon would be nowhere to be seen! I would need to put in something around a 30x eyepiece to fit both in the same view, and of course the Earth would appear about 3 times smaller.
Interesting thought isn't it! So I wonder if Earth has the largest satellite separation in planetary diameters, for large moons though, I think even Jupiter has stacks of Moons more than 30 diameters away but they would not be visible in a backyard telescope. I must do a couple of calculations for Saturn, Neptune, Uranus. Or does someone have the figures to hand?
How far from Jupiter are it's moons, compared to the distance between us and our moon? I guess he meant in terms of planet diameters. So last night I did a quick lookup of some stats and came to the following very rough ball park figure.
The Moons orbit is about 30 Earth diameters.
Callisto's orbit is about 12 Jupiter diameters.
So....if you were on another planet viewing the Earth with a magnification that would make Earth appear roughly the same size as you normally see Jupiter, our moon would appear almost 3 times further away from the Earth as what Callisto appears when it is at its furthest separation. With the normal sorts of magnifications (~100x) I use for viewing Jupiter, I can fit all the moons in the view confortably. But at the same image size, the Earths moon would be nowhere to be seen! I would need to put in something around a 30x eyepiece to fit both in the same view, and of course the Earth would appear about 3 times smaller.
Interesting thought isn't it! So I wonder if Earth has the largest satellite separation in planetary diameters, for large moons though, I think even Jupiter has stacks of Moons more than 30 diameters away but they would not be visible in a backyard telescope. I must do a couple of calculations for Saturn, Neptune, Uranus. Or does someone have the figures to hand?