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?
Interesting topic, and great question for someone to ask, especially a youngster! I like the way you tackled the comparison there.
Our moon is also quite large when you compare it's diameter to that of the earth.
I seem to recall reading somewhere our moon is the largest in the solar system when compared that way, ie moon diameter against parent body diameter. Now that Charon and Pluto no longer officially form a planetary system I don't there's anything else that even comes close.
Why would a kid ask how many planet diameters is it's moon away???
Trevor, I think you be puttin words in his mouth!
I would think he means in 'kilometres' or some simple measuring system a kid can understand like how many Holden Commodores, or how many drinking straws end-to-end
Why would a kid ask how many planet diameters is it's moon away???
Trevor, I think you be puttin words in his mouth!
I would think he means in 'kilometres' or some simple measuring system a kid can understand like how many Holden Commodores, or how many drinking straws end-to-end
Actually, I was thinking he was asking something like that too. But he clarified the question a bit more, I must admit his dad helped a bit. His dad said something like "I think he wants to know compared to our planet are they a long way away, because Jupiter is much larger than the earth?" The same kid also asked how long do they take to make an orbit, and where was the red spot, how big were the "storms" and heaps of others that I sort of tried to change the subject. The kid was a bit too smart for me
