Orrery

[Solanum]

Anyone know of a reasonably priced orrery that I can get for the kids? I'd want at least the eight planets, preferably with some semblance of relative distances and definitely with the correct relative orbital speeds. I have only seen rather expensive, very decorative jobs, so perhaps no one makes one?

[renormalised]

Not offhand, sorry. There is that one that you can make yourself from parts included with a magazine (can't remember the name). But I'm not sure how good or accurate it is.

[Blue Skies]

I think its a virtual impossibility to get one with good relative distances. If you have a play with the model generator in the link below, you quickly see that unless you have Mercury as a speck of dust right next to the sun your model stretches to metres wide very quickly. You can ignore the planet sizes but relative distances is a bummer to do right. You might have to go digital to get what you want.

http://www.exploratorium.edu/ronh/solar_system/

[Wavytone]

It's physically impractical to make a mechanical one that is to linear scale.

You could however use logarithmic scale for the orbit radius, and construct a reasonably compact one that does the orbital periods in their correct ratios.

But such a thing is not made/sold commercially.

[dannat]

there is one you put together from a magazine total cost about $700, all brass constrcution, all p-laets & moon & galilean moons if i remmeber rightly

[Solanum]

Yeah, I realise that, that's why I said some "semblance" :) I was thinking of a log scale of some sort (would have to be bigger than log10 I guess!), but it is the periods that are more important. I have seen a couple of cheap ones that have them all going round together, which seems pretty pointless in my book!

The cheapest I've seen which has the correct relative periods was US$260 and that had all the planets evenly spaced (though the sizes were scaled).